diff options
| author |   Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2017-04-05 10:22:57 -0300 |
|---|---|---|
| committer |   Jonathan Corbet <corbet@lwn.net> | 2017-04-11 14:37:04 -0600 |
| commit | 4ad4b21b1b81ce215c1d45850bd5a67e2179c60a (patch) | |
| tree | 96ff7ca62e81affaf9f1b20247c3d73f50e55a56 /Documentation/DocBook | |
| parent | driver-api/basics.rst: add device table header (diff) | |
| download | wireguard-linux-4ad4b21b1b81ce215c1d45850bd5a67e2179c60a.tar.xz wireguard-linux-4ad4b21b1b81ce215c1d45850bd5a67e2179c60a.zip | |
docs-rst: convert usb docbooks to ReST
As we're moving out of DocBook, let's convert the remaining
USB docbooks to ReST.
The transformation itself on this patch is a no-brainer
conversion using pandoc via this script:
Documentation/sphinx/tmplcvt
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 7 | ||||
| -rw-r--r-- | Documentation/DocBook/gadget.tmpl | 793 | ||||
| -rw-r--r-- | Documentation/DocBook/writing_musb_glue_layer.tmpl | 873 | ||||
| -rw-r--r-- | Documentation/DocBook/writing_usb_driver.tmpl | 412 |
4 files changed, 3 insertions, 2082 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 4a81e7a78e23..13056d40e11b 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -8,12 +8,11 @@ DOCBOOKS := z8530book.xml \ kernel-hacking.xml kernel-locking.xml \ - writing_usb_driver.xml networking.xml \ + networking.xml \ filesystems.xml lsm.xml kgdb.xml \ - gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ + libata.xml mtdnand.xml librs.xml rapidio.xml \ s390-drivers.xml scsi.xml \ - sh.xml w1.xml \ - writing_musb_glue_layer.xml + sh.xml w1.xml ifeq ($(DOCBOOKS),) diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl deleted file mode 100644 index 641629221176..000000000000 --- a/Documentation/DocBook/gadget.tmpl +++ /dev/null @@ -1,793 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> - -<book id="USB-Gadget-API"> - <bookinfo> - <title>USB Gadget API for Linux</title> - <date>20 August 2004</date> - <edition>20 August 2004</edition> - - <legalnotice> - <para> - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later - version. - </para> - - <para> - This program is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - </para> - - <para> - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - </para> - - <para> - For more details see the file COPYING in the source - distribution of Linux. - </para> - </legalnotice> - <copyright> - <year>2003-2004</year> - <holder>David Brownell</holder> - </copyright> - - <author> - <firstname>David</firstname> - <surname>Brownell</surname> - <affiliation> - <address><email>dbrownell@users.sourceforge.net</email></address> - </affiliation> - </author> - </bookinfo> - -<toc></toc> - -<chapter id="intro"><title>Introduction</title> - -<para>This document presents a Linux-USB "Gadget" -kernel mode -API, for use within peripherals and other USB devices -that embed Linux. -It provides an overview of the API structure, -and shows how that fits into a system development project. -This is the first such API released on Linux to address -a number of important problems, including: </para> - -<itemizedlist> - <listitem><para>Supports USB 2.0, for high speed devices which - can stream data at several dozen megabytes per second. - </para></listitem> - <listitem><para>Handles devices with dozens of endpoints just as - well as ones with just two fixed-function ones. Gadget drivers - can be written so they're easy to port to new hardware. - </para></listitem> - <listitem><para>Flexible enough to expose more complex USB device - capabilities such as multiple configurations, multiple interfaces, - composite devices, - and alternate interface settings. - </para></listitem> - <listitem><para>USB "On-The-Go" (OTG) support, in conjunction - with updates to the Linux-USB host side. - </para></listitem> - <listitem><para>Sharing data structures and API models with the - Linux-USB host side API. This helps the OTG support, and - looks forward to more-symmetric frameworks (where the same - I/O model is used by both host and device side drivers). - </para></listitem> - <listitem><para>Minimalist, so it's easier to support new device - controller hardware. I/O processing doesn't imply large - demands for memory or CPU resources. - </para></listitem> -</itemizedlist> - - -<para>Most Linux developers will not be able to use this API, since they -have USB "host" hardware in a PC, workstation, or server. -Linux users with embedded systems are more likely to -have USB peripheral hardware. -To distinguish drivers running inside such hardware from the -more familiar Linux "USB device drivers", -which are host side proxies for the real USB devices, -a different term is used: -the drivers inside the peripherals are "USB gadget drivers". -In USB protocol interactions, the device driver is the master -(or "client driver") -and the gadget driver is the slave (or "function driver"). -</para> - -<para>The gadget API resembles the host side Linux-USB API in that both -use queues of request objects to package I/O buffers, and those requests -may be submitted or canceled. -They share common definitions for the standard USB -<emphasis>Chapter 9</emphasis> messages, structures, and constants. -Also, both APIs bind and unbind drivers to devices. -The APIs differ in detail, since the host side's current -URB framework exposes a number of implementation details -and assumptions that are inappropriate for a gadget API. -While the model for control transfers and configuration -management is necessarily different (one side is a hardware-neutral master, -the other is a hardware-aware slave), the endpoint I/0 API used here -should also be usable for an overhead-reduced host side API. -</para> - -</chapter> - -<chapter id="structure"><title>Structure of Gadget Drivers</title> - -<para>A system running inside a USB peripheral -normally has at least three layers inside the kernel to handle -USB protocol processing, and may have additional layers in -user space code. -The "gadget" API is used by the middle layer to interact -with the lowest level (which directly handles hardware). -</para> - -<para>In Linux, from the bottom up, these layers are: -</para> - -<variablelist> - - <varlistentry> - <term><emphasis>USB Controller Driver</emphasis></term> - - <listitem> - <para>This is the lowest software level. - It is the only layer that talks to hardware, - through registers, fifos, dma, irqs, and the like. - The <filename><linux/usb/gadget.h></filename> API abstracts - the peripheral controller endpoint hardware. - That hardware is exposed through endpoint objects, which accept - streams of IN/OUT buffers, and through callbacks that interact - with gadget drivers. - Since normal USB devices only have one upstream - port, they only have one of these drivers. - The controller driver can support any number of different - gadget drivers, but only one of them can be used at a time. - </para> - - <para>Examples of such controller hardware include - the PCI-based NetChip 2280 USB 2.0 high speed controller, - the SA-11x0 or PXA-25x UDC (found within many PDAs), - and a variety of other products. - </para> - - </listitem></varlistentry> - - <varlistentry> - <term><emphasis>Gadget Driver</emphasis></term> - - <listitem> - <para>The lower boundary of this driver implements hardware-neutral - USB functions, using calls to the controller driver. - Because such hardware varies widely in capabilities and restrictions, - and is used in embedded environments where space is at a premium, - the gadget driver is often configured at compile time - to work with endpoints supported by one particular controller. - Gadget drivers may be portable to several different controllers, - using conditional compilation. - (Recent kernels substantially simplify the work involved in - supporting new hardware, by <emphasis>autoconfiguring</emphasis> - endpoints automatically for many bulk-oriented drivers.) - Gadget driver responsibilities include: - </para> - <itemizedlist> - <listitem><para>handling setup requests (ep0 protocol responses) - possibly including class-specific functionality - </para></listitem> - <listitem><para>returning configuration and string descriptors - </para></listitem> - <listitem><para>(re)setting configurations and interface - altsettings, including enabling and configuring endpoints - </para></listitem> - <listitem><para>handling life cycle events, such as managing - bindings to hardware, - USB suspend/resume, remote wakeup, - and disconnection from the USB host. - </para></listitem> - <listitem><para>managing IN and OUT transfers on all currently - enabled endpoints - </para></listitem> - </itemizedlist> - - <para> - Such drivers may be modules of proprietary code, although - that approach is discouraged in the Linux community. - </para> - </listitem></varlistentry> - - <varlistentry> - <term><emphasis>Upper Level</emphasis></term> - - <listitem> - <para>Most gadget drivers have an upper boundary that connects - to some Linux driver or framework in Linux. - Through that boundary flows the data which the gadget driver - produces and/or consumes through protocol transfers over USB. - Examples include: - </para> - <itemizedlist> - <listitem><para>user mode code, using generic (gadgetfs) - or application specific files in - <filename>/dev</filename> - </para></listitem> - <listitem><para>networking subsystem (for network gadgets, - like the CDC Ethernet Model gadget driver) - </para></listitem> - <listitem><para>data capture drivers, perhaps video4Linux or - a scanner driver; or test and measurement hardware. - </para></listitem> - <listitem><para>input subsystem (for HID gadgets) - </para></listitem> - <listitem><para>sound subsystem (for audio gadgets) - </para></listitem> - <listitem><para>file system (for PTP gadgets) - </para></listitem> - <listitem><para>block i/o subsystem (for usb-storage gadgets) - </para></listitem> - <listitem><para>... and more </para></listitem> - </itemizedlist> - </listitem></varlistentry> - - <varlistentry> - <term><emphasis>Additional Layers</emphasis></term> - - <listitem> - <para>Other layers may exist. - These could include kernel layers, such as network protocol stacks, - as well as user mode applications building on standard POSIX - system call APIs such as - <emphasis>open()</emphasis>, <emphasis>close()</emphasis>, - <emphasis>read()</emphasis> and <emphasis>write()</emphasis>. - On newer systems, POSIX Async I/O calls may be an option. - Such user mode code will not necessarily be subject to - the GNU General Public License (GPL). - </para> - </listitem></varlistentry> - - -</variablelist> - -<para>OTG-capable systems will also need to include a standard Linux-USB -host side stack, -with <emphasis>usbcore</emphasis>, -one or more <emphasis>Host Controller Drivers</emphasis> (HCDs), -<emphasis>USB Device Drivers</emphasis> to support -the OTG "Targeted Peripheral List", -and so forth. -There will also be an <emphasis>OTG Controller Driver</emphasis>, -which is visible to gadget and device driver developers only indirectly. -That helps the host and device side USB controllers implement the -two new OTG protocols (HNP and SRP). -Roles switch (host to peripheral, or vice versa) using HNP -during USB suspend processing, and SRP can be viewed as a -more battery-friendly kind of device wakeup protocol. -</para> - -<para>Over time, reusable utilities are evolving to help make some -gadget driver tasks simpler. -For example, building configuration descriptors from vectors of -descriptors for the configurations interfaces and endpoints is -now automated, and many drivers now use autoconfiguration to -choose hardware endpoints and initialize their descriptors. - -A potential example of particular interest -is code implementing standard USB-IF protocols for -HID, networking, storage, or audio classes. -Some developers are interested in KDB or KGDB hooks, to let -target hardware be remotely debugged. -Most such USB protocol code doesn't need to be hardware-specific, -any more than network protocols like X11, HTTP, or NFS are. -Such gadget-side interface drivers should eventually be combined, -to implement composite devices. -</para> - -</chapter> - - -<chapter id="api"><title>Kernel Mode Gadget API</title> - -<para>Gadget drivers declare themselves through a -<emphasis>struct usb_gadget_driver</emphasis>, which is responsible for -most parts of enumeration for a <emphasis>struct usb_gadget</emphasis>. -The response to a set_configuration usually involves -enabling one or more of the <emphasis>struct usb_ep</emphasis> objects -exposed by the gadget, and submitting one or more -<emphasis>struct usb_request</emphasis> buffers to transfer data. -Understand those four data types, and their operations, and -you will understand how this API works. -</para> - -<note><title>Incomplete Data Type Descriptions</title> - -<para>This documentation was prepared using the standard Linux -kernel <filename>docproc</filename> tool, which turns text -and in-code comments into SGML DocBook and then into usable -formats such as HTML or PDF. -Other than the "Chapter 9" data types, most of the significant -data types and functions are described here. -</para> - -<para>However, docproc does not understand all the C constructs -that are used, so some relevant information is likely omitted from -what you are reading. -One example of such information is endpoint autoconfiguration. -You'll have to read the header file, and use example source -code (such as that for "Gadget Zero"), to fully understand the API. -</para> - -<para>The part of the API implementing some basic -driver capabilities is specific to the version of the -Linux kernel that's in use. -The 2.6 kernel includes a <emphasis>driver model</emphasis> -framework that has no analogue on earlier kernels; -so those parts of the gadget API are not fully portable. -(They are implemented on 2.4 kernels, but in a different way.) -The driver model state is another part of this API that is -ignored by the kerneldoc tools. -</para> -</note> - -<para>The core API does not expose -every possible hardware feature, only the most widely available ones. -There are significant hardware features, such as device-to-device DMA -(without temporary storage in a memory buffer) -that would be added using hardware-specific APIs. -</para> - -<para>This API allows drivers to use conditional compilation to handle -endpoint capabilities of different hardware, but doesn't require that. -Hardware tends to have arbitrary restrictions, relating to -transfer types, addressing, packet sizes, buffering, and availability. -As a rule, such differences only matter for "endpoint zero" logic -that handles device configuration and management. -The API supports limited run-time -detection of capabilities, through naming conventions for endpoints. -Many drivers will be able to at least partially autoconfigure -themselves. -In particular, driver init sections will often have endpoint -autoconfiguration logic that scans the hardware's list of endpoints -to find ones matching the driver requirements -(relying on those conventions), to eliminate some of the most -common reasons for conditional compilation. -</para> - -<para>Like the Linux-USB host side API, this API exposes -the "chunky" nature of USB messages: I/O requests are in terms -of one or more "packets", and packet boundaries are visible to drivers. -Compared to RS-232 serial protocols, USB resembles -synchronous protocols like HDLC -(N bytes per frame, multipoint addressing, host as the primary -station and devices as secondary stations) -more than asynchronous ones -(tty style: 8 data bits per frame, no parity, one stop bit). -So for example the controller drivers won't buffer -two single byte writes into a single two-byte USB IN packet, -although gadget drivers may do so when they implement -protocols where packet boundaries (and "short packets") -are not significant. -</para> - -<sect1 id="lifecycle"><title>Driver Life Cycle</title> - -<para>Gadget drivers make endpoint I/O requests to hardware without -needing to know many details of the hardware, but driver -setup/configuration code needs to handle some differences. -Use the API like this: -</para> - -<orderedlist numeration='arabic'> - -<listitem><para>Register a driver for the particular device side -usb controller hardware, -such as the net2280 on PCI (USB 2.0), -sa11x0 or pxa25x as found in Linux PDAs, -and so on. -At this point the device is logically in the USB ch9 initial state -("attached"), drawing no power and not usable -(since it does not yet support enumeration). -Any host should not see the device, since it's not -activated the data line pullup used by the host to -detect a device, even if VBUS power is available. -</para></listitem> - -<listitem><para>Register a gadget driver that implements some higher level -device function. That will then bind() to a usb_gadget, which -activates the data line pullup sometime after detecting VBUS. -</para></listitem> - -<listitem><para>The hardware driver can now start enumerating. -The steps it handles are to accept USB power and set_address requests. -Other steps are handled by the gadget driver. -If the gadget driver module is unloaded before the host starts to -enumerate, steps before step 7 are skipped. -</para></listitem> - -<listitem><para>The gadget driver's setup() call returns usb descriptors, -based both on what the bus interface hardware provides and on the -functionality being implemented. -That can involve alternate settings or configurations, -unless the hardware prevents such operation. -For OTG devices, each configuration descriptor includes -an OTG descriptor. -</para></listitem> - -<listitem><para>The gadget driver handles the last step of enumeration, -when the USB host issues a set_configuration call. -It enables all endpoints used in that configuration, -with all interfaces in their default settings. -That involves using a list of the hardware's endpoints, enabling each -endpoint according to its descriptor. -It may also involve using <function>usb_gadget_vbus_draw</function> -to let more power be drawn from VBUS, as allowed by that configuration. -For OTG devices, setting a configuration may also involve reporting -HNP capabilities through a user interface. -</para></listitem> - -<listitem><para>Do real work and perform data transfers, possibly involving -changes to interface settings or switching to new configurations, until the -device is disconnect()ed from the host. -Queue any number of transfer requests to each endpoint. -It may be suspended and resumed several times before being disconnected. -On disconnect, the drivers go back to step 3 (above). -</para></listitem> - -<listitem><para>When the gadget driver module is being unloaded, -the driver unbind() callback is issued. That lets the controller -driver be unloaded. -</para></listitem> - -</orderedlist> - -<para>Drivers will normally be arranged so that just loading the -gadget driver module (or statically linking it into a Linux kernel) -allows the peripheral device to be enumerated, but some drivers -will defer enumeration until some higher level component (like -a user mode daemon) enables it. -Note that at this lowest level there are no policies about how -ep0 configuration logic is implemented, -except that it should obey USB specifications. -Such issues are in the domain of gadget drivers, -including knowing about implementation constraints -imposed by some USB controllers -or understanding that composite devices might happen to -be built by integrating reusable components. -</para> - -<para>Note that the lifecycle above can be slightly different -for OTG devices. -Other than providing an additional OTG descriptor in each -configuration, only the HNP-related differences are particularly -visible to driver code. -They involve reporting requirements during the SET_CONFIGURATION -request, and the option to invoke HNP during some suspend callbacks. -Also, SRP changes the semantics of -<function>usb_gadget_wakeup</function> -slightly. -</para> - -</sect1> - -<sect1 id="ch9"><title>USB 2.0 Chapter 9 Types and Constants</title> - -<para>Gadget drivers -rely on common USB structures and constants -defined in the -<filename><linux/usb/ch9.h></filename> -header file, which is standard in Linux 2.6 kernels. -These are the same types and constants used by host -side drivers (and usbcore). -</para> - -!Iinclude/linux/usb/ch9.h -</sect1> - -<sect1 id="core"><title>Core Objects and Methods</title> - -<para>These are declared in -<filename><linux/usb/gadget.h></filename>, -and are used by gadget drivers to interact with -USB peripheral controller drivers. -</para> - - <!-- yeech, this is ugly in nsgmls PDF output. - - the PDF bookmark and refentry output nesting is wrong, - and the member/argument documentation indents ugly. - - plus something (docproc?) adds whitespace before the - descriptive paragraph text, so it can't line up right - unless the explanations are trivial. - --> - -!Iinclude/linux/usb/gadget.h -</sect1> - -<sect1 id="utils"><title>Optional Utilities</title> - -<para>The core API is sufficient for writing a USB Gadget Driver, -but some optional utilities are provided to simplify common tasks. -These utilities include endpoint autoconfiguration. -</para> - -!Edrivers/usb/gadget/usbstring.c -!Edrivers/usb/gadget/config.c -<!-- !Edrivers/usb/gadget/epautoconf.c --> -</sect1> - -<sect1 id="composite"><title>Composite Device Framework</title> - -<para>The core API is sufficient for writing drivers for composite -USB devices (with more than one function in a given configuration), -and also multi-configuration devices (also more than one function, -but not necessarily sharing a given configuration). -There is however an optional framework which makes it easier to -reuse and combine functions. -</para> - -<para>Devices using this framework provide a <emphasis>struct -usb_composite_driver</emphasis>, which in turn provides one or -more <emphasis>struct usb_configuration</emphasis> instances. -Each such configuration includes at least one -<emphasis>struct usb_function</emphasis>, which packages a user -visible role such as "network link" or "mass storage device". -Management functions may also exist, such as "Device Firmware -Upgrade". -</para> - -!Iinclude/linux/usb/composite.h -!Edrivers/usb/gadget/composite.c - -</sect1> - -<sect1 id="functions"><title>Composite Device Functions</title> - -<para>At this writing, a few of the current gadget drivers have -been converted to this framework. -Near-term plans include converting all of them, except for "gadgetfs". -</para> - -!Edrivers/usb/gadget/function/f_acm.c -!Edrivers/usb/gadget/function/f_ecm.c -!Edrivers/usb/gadget/function/f_subset.c -!Edrivers/usb/gadget/function/f_obex.c -!Edrivers/usb/gadget/function/f_serial.c - -</sect1> - - -</chapter> - -<chapter id="controllers"><title>Peripheral Controller Drivers</title> - -<para>The first hardware supporting this API was the NetChip 2280 -controller, which supports USB 2.0 high speed and is based on PCI. -This is the <filename>net2280</filename> driver module. -The driver supports Linux kernel versions 2.4 and 2.6; -contact NetChip Technologies for development boards and product -information. -</para> - -<para>Other hardware working in the "gadget" framework includes: -Intel's PXA 25x and IXP42x series processors -(<filename>pxa2xx_udc</filename>), -Toshiba TC86c001 "Goku-S" (<filename>goku_udc</filename>), -Renesas SH7705/7727 (<filename>sh_udc</filename>), -MediaQ 11xx (<filename>mq11xx_udc</filename>), -Hynix HMS30C7202 (<filename>h7202_udc</filename>), -National 9303/4 (<filename>n9604_udc</filename>), -Texas Instruments OMAP (<filename>omap_udc</filename>), -Sharp LH7A40x (<filename>lh7a40x_udc</filename>), -and more. -Most of those are full speed controllers. -</para> - -<para>At this writing, there are people at work on drivers in -this framework for several other USB device controllers, -with plans to make many of them be widely available. -</para> - -<!-- !Edrivers/usb/gadget/net2280.c --> - -<para>A partial USB simulator, -the <filename>dummy_hcd</filename> driver, is available. -It can act like a net2280, a pxa25x, or an sa11x0 in terms -of available endpoints and device speeds; and it simulates -control, bulk, and to some extent interrupt transfers. -That lets you develop some parts of a gadget driver on a normal PC, -without any special hardware, and perhaps with the assistance -of tools such as GDB running with User Mode Linux. -At least one person has expressed interest in adapting that -approach, hooking it up to a simulator for a microcontroller. -Such simulators can help debug subsystems where the runtime hardware -is unfriendly to software development, or is not yet available. -</para> - -<para>Support for other controllers is expected to be developed -and contributed -over time, as this driver framework evolves. -</para> - -</chapter> - -<chapter id="gadget"><title>Gadget Drivers</title> - -<para>In addition to <emphasis>Gadget Zero</emphasis> -(used primarily for testing and development with drivers -for usb controller hardware), other gadget drivers exist. -</para> - -<para>There's an <emphasis>ethernet</emphasis> gadget -driver, which implements one of the most useful -<emphasis>Communications Device Class</emphasis> (CDC) models. -One of the standards for cable modem interoperability even -specifies the use of this ethernet model as one of two -mandatory options. -Gadgets using this code look to a USB host as if they're -an Ethernet adapter. -It provides access to a network where the gadget's CPU is one host, -which could easily be bridging, routing, or firewalling -access to other networks. -Since some hardware can't fully implement the CDC Ethernet -requirements, this driver also implements a "good parts only" -subset of CDC Ethernet. -(That subset doesn't advertise itself as CDC Ethernet, -to avoid creating problems.) -</para> - -<para>Support for Microsoft's <emphasis>RNDIS</emphasis> -protocol has been contributed by Pengutronix and Auerswald GmbH. -This is like CDC Ethernet, but it runs on more slightly USB hardware -(but less than the CDC subset). -However, its main claim to fame is being able to connect directly to -recent versions of Windows, using drivers that Microsoft bundles -and supports, making it much simpler to network with Windows. -</para> - -<para>There is also support for user mode gadget drivers, -using <emphasis>gadgetfs</emphasis>. -This provides a <emphasis>User Mode API</emphasis> that presents -each endpoint as a single file descriptor. I/O is done using -normal <emphasis>read()</emphasis> and <emphasis>read()</emphasis> calls. -Familiar tools like GDB and pthreads can be used to -develop and debug user mode drivers, so that once a robust -controller driver is available many applications for it -won't require new kernel mode software. -Linux 2.6 <emphasis>Async I/O (AIO)</emphasis> -support is available, so that user mode software -can stream data with only slightly more overhead -than a kernel driver. -</para> - -<para>There's a USB Mass Storage class driver, which provides -a different solution for interoperability with systems such -as MS-Windows and MacOS. -That <emphasis>Mass Storage</emphasis> driver uses a -file or block device as backing store for a drive, -like the <filename>loop</filename> driver. -The USB host uses the BBB, CB, or CBI versions of the mass -storage class specification, using transparent SCSI commands -to access the data from the backing store. -</para> - -<para>There's a "serial line" driver, useful for TTY style -operation over USB. -The latest version of that driver supports CDC ACM style -operation, like a USB modem, and so on most hardware it can -interoperate easily with MS-Windows. -One interesting use of that driver is in boot firmware (like a BIOS), -which can sometimes use that model with very small systems without -real serial lines. -</para> - -<para>Support for other kinds of gadget is expected to -be developed and contributed -over time, as this driver framework evolves. -</para> - -</chapter> - -<chapter id="otg"><title>USB On-The-GO (OTG)</title> - -<para>USB OTG support on Linux 2.6 was initially developed -by Texas Instruments for -<ulink url="http://www.omap.com">OMAP</ulink> 16xx and 17xx -series processors. -Other OTG systems should work in similar ways, but the -hardware level details could be very different. -</para> - -<para>Systems need specialized hardware support to implement OTG, -notably including a special <emphasis>Mini-AB</emphasis> jack -and associated transceiver to support <emphasis>Dual-Role</emphasis> -operation: -they can act either as a host, using the standard -Linux-USB host side driver stack, -or as a peripheral, using this "gadget" framework. -To do that, the system software relies on small additions -to those programming interfaces, -and on a new internal component (here called an "OTG Controller") -affecting which driver stack connects to the OTG port. -In each role, the system can re-use the existing pool of -hardware-neutral drivers, layered on top of the controller -driver interfaces (<emphasis>usb_bus</emphasis> or -<emphasis>usb_gadget</emphasis>). -Such drivers need at most minor changes, and most of the calls -added to support OTG can also benefit non-OTG products. -</para> - -<itemizedlist> - <listitem><para>Gadget drivers test the <emphasis>is_otg</emphasis> - flag, and use it to determine whether or not to include - an OTG descriptor in each of their configurations. - </para></listitem> - <listitem><para>Gadget drivers may need changes to support the - two new OTG protocols, exposed in new gadget attributes - such as <emphasis>b_hnp_enable</emphasis> flag. - HNP support should be reported through a user interface - (two LEDs could suffice), and is triggered in some cases - when the host suspends the peripheral. - SRP support can be user-initiated just like remote wakeup, - probably by pressing the same button. - </para></listitem> - <listitem><para>On the host side, USB device drivers need - to be taught to trigger HNP at appropriate moments, using - <function>usb_suspend_device()</function>. - That also conserves battery power, which is useful even - for non-OTG configurations. - </para></listitem> - <listitem><para>Also on the host side, a driver must support the - OTG "Targeted Peripheral List". That's just a whitelist, - used to reject peripherals not supported with a given - Linux OTG host. - <emphasis>This whitelist is product-specific; - each product must modify <filename>otg_whitelist.h</filename> - to match its interoperability specification. - </emphasis> - </para> - <para>Non-OTG Linux hosts, like PCs and workstations, - normally have some solution for adding drivers, so that - peripherals that aren't recognized can eventually be supported. - That approach is unreasonable for consumer products that may - never have their firmware upgraded, and where it's usually - unrealistic to expect traditional PC/workstation/server kinds - of support model to work. - For example, it's often impractical to change device firmware - once the product has been distributed, so driver bugs can't - normally be fixed if they're found after shipment. - </para></listitem> -</itemizedlist> - -<para> -Additional changes are needed below those hardware-neutral -<emphasis>usb_bus</emphasis> and <emphasis>usb_gadget</emphasis> -driver interfaces; those aren't discussed here in any detail. -Those affect the hardware-specific code for each USB Host or Peripheral -controller, and how the HCD initializes (since OTG can be active only -on a single port). -They also involve what may be called an <emphasis>OTG Controller -Driver</emphasis>, managing the OTG transceiver and the OTG state -machine logic as well as much of the root hub behavior for the -OTG port. -The OTG controller driver needs to activate and deactivate USB -controllers depending on the relevant device role. -Some related changes were needed inside usbcore, so that it -can identify OTG-capable devices and respond appropriately -to HNP or SRP protocols. -</para> - -</chapter> - -</book> -<!-- - vim:syntax=sgml:sw=4 ---> diff --git a/Documentation/DocBook/writing_musb_glue_layer.tmpl b/Documentation/DocBook/writing_musb_glue_layer.tmpl deleted file mode 100644 index 837eca77f274..000000000000 --- a/Documentation/DocBook/writing_musb_glue_layer.tmpl +++ /dev/null @@ -1,873 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> - -<book id="Writing-MUSB-Glue-Layer"> - <bookinfo> - <title>Writing an MUSB Glue Layer</title> - - <authorgroup> - <author> - <firstname>Apelete</firstname> - <surname>Seketeli</surname> - <affiliation> - <address> - <email>apelete at seketeli.net</email> - </address> - </affiliation> - </author> - </authorgroup> - - <copyright> - <year>2014</year> - <holder>Apelete Seketeli</holder> - </copyright> - - <legalnotice> - <para> - This documentation is free software; you can redistribute it - and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later version. - </para> - - <para> - This documentation is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - </para> - - <para> - You should have received a copy of the GNU General Public License - along with this documentation; if not, write to the Free Software - Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA - 02111-1307 USA - </para> - - <para> - For more details see the file COPYING in the Linux kernel source - tree. - </para> - </legalnotice> - </bookinfo> - -<toc></toc> - - <chapter id="introduction"> - <title>Introduction</title> - <para> - The Linux MUSB subsystem is part of the larger Linux USB - subsystem. It provides support for embedded USB Device Controllers - (UDC) that do not use Universal Host Controller Interface (UHCI) - or Open Host Controller Interface (OHCI). - </para> - <para> - Instead, these embedded UDC rely on the USB On-the-Go (OTG) - specification which they implement at least partially. The silicon - reference design used in most cases is the Multipoint USB - Highspeed Dual-Role Controller (MUSB HDRC) found in the Mentor - Graphics Inventra™ design. - </para> - <para> - As a self-taught exercise I have written an MUSB glue layer for - the Ingenic JZ4740 SoC, modelled after the many MUSB glue layers - in the kernel source tree. This layer can be found at - drivers/usb/musb/jz4740.c. In this documentation I will walk - through the basics of the jz4740.c glue layer, explaining the - different pieces and what needs to be done in order to write your - own device glue layer. - </para> - </chapter> - - <chapter id="linux-musb-basics"> - <title>Linux MUSB Basics</title> - <para> - To get started on the topic, please read USB On-the-Go Basics (see - Resources) which provides an introduction of USB OTG operation at - the hardware level. A couple of wiki pages by Texas Instruments - and Analog Devices also provide an overview of the Linux kernel - MUSB configuration, albeit focused on some specific devices - provided by these companies. Finally, getting acquainted with the - USB specification at USB home page may come in handy, with - practical instance provided through the Writing USB Device Drivers - documentation (again, see Resources). - </para> - <para> - Linux USB stack is a layered architecture in which the MUSB - controller hardware sits at the lowest. The MUSB controller driver - abstract the MUSB controller hardware to the Linux USB stack. - </para> - <programlisting> - ------------------------ - | | <------- drivers/usb/gadget - | Linux USB Core Stack | <------- drivers/usb/host - | | <------- drivers/usb/core - ------------------------ - ⬍ - -------------------------- - | | <------ drivers/usb/musb/musb_gadget.c - | MUSB Controller driver | <------ drivers/usb/musb/musb_host.c - | | <------ drivers/usb/musb/musb_core.c - -------------------------- - ⬍ - --------------------------------- - | MUSB Platform Specific Driver | - | | <-- drivers/usb/musb/jz4740.c - | aka "Glue Layer" | - --------------------------------- - ⬍ - --------------------------------- - | MUSB Controller Hardware | - --------------------------------- - </programlisting> - <para> - As outlined above, the glue layer is actually the platform - specific code sitting in between the controller driver and the - controller hardware. - </para> - <para> - Just like a Linux USB driver needs to register itself with the - Linux USB subsystem, the MUSB glue layer needs first to register - itself with the MUSB controller driver. This will allow the - controller driver to know about which device the glue layer - supports and which functions to call when a supported device is - detected or released; remember we are talking about an embedded - controller chip here, so no insertion or removal at run-time. - </para> - <para> - All of this information is passed to the MUSB controller driver - through a platform_driver structure defined in the glue layer as: - </para> - <programlisting linenumbering="numbered"> -static struct platform_driver jz4740_driver = { - .probe = jz4740_probe, - .remove = jz4740_remove, - .driver = { - .name = "musb-jz4740", - }, -}; - </programlisting> - <para> - The probe and remove function pointers are called when a matching - device is detected and, respectively, released. The name string - describes the device supported by this glue layer. In the current - case it matches a platform_device structure declared in - arch/mips/jz4740/platform.c. Note that we are not using device - tree bindings here. - </para> - <para> - In order to register itself to the controller driver, the glue - layer goes through a few steps, basically allocating the - controller hardware resources and initialising a couple of - circuits. To do so, it needs to keep track of the information used - throughout these steps. This is done by defining a private - jz4740_glue structure: - </para> - <programlisting linenumbering="numbered"> -struct jz4740_glue { - struct device *dev; - struct platform_device *musb; - struct clk *clk; -}; - </programlisting> - <para> - The dev and musb members are both device structure variables. The - first one holds generic information about the device, since it's - the basic device structure, and the latter holds information more - closely related to the subsystem the device is registered to. The - clk variable keeps information related to the device clock - operation. - </para> - <para> - Let's go through the steps of the probe function that leads the - glue layer to register itself to the controller driver. - </para> - <para> - N.B.: For the sake of readability each function will be split in - logical parts, each part being shown as if it was independent from - the others. - </para> - <programlisting linenumbering="numbered"> -static int jz4740_probe(struct platform_device *pdev) -{ - struct platform_device *musb; - struct jz4740_glue *glue; - struct clk *clk; - int ret; - - glue = devm_kzalloc(&pdev->dev, sizeof(*glue), GFP_KERNEL); - if (!glue) - return -ENOMEM; - - musb = platform_device_alloc("musb-hdrc", PLATFORM_DEVID_AUTO); - if (!musb) { - dev_err(&pdev->dev, "failed to allocate musb device\n"); - return -ENOMEM; - } - - clk = devm_clk_get(&pdev->dev, "udc"); - if (IS_ERR(clk)) { - dev_err(&pdev->dev, "failed to get clock\n"); - ret = PTR_ERR(clk); - goto err_platform_device_put; - } - - ret = clk_prepare_enable(clk); - if (ret) { - dev_err(&pdev->dev, "failed to enable clock\n"); - goto err_platform_device_put; - } - - musb->dev.parent = &pdev->dev; - - glue->dev = &pdev->dev; - glue->musb = musb; - glue->clk = clk; - - return 0; - -err_platform_device_put: - platform_device_put(musb); - return ret; -} - </programlisting> - <para> - The first few lines of the probe function allocate and assign the - glue, musb and clk variables. The GFP_KERNEL flag (line 8) allows - the allocation process to sleep and wait for memory, thus being - usable in a blocking situation. The PLATFORM_DEVID_AUTO flag (line - 12) allows automatic allocation and management of device IDs in - order to avoid device namespace collisions with explicit IDs. With - devm_clk_get() (line 18) the glue layer allocates the clock -- the - <literal>devm_</literal> prefix indicates that clk_get() is - managed: it automatically frees the allocated clock resource data - when the device is released -- and enable it. - </para> - <para> - Then comes the registration steps: - </para> - <programlisting linenumbering="numbered"> -static int jz4740_probe(struct platform_device *pdev) -{ - struct musb_hdrc_platform_data *pdata = &jz4740_musb_platform_data; - - pdata->platform_ops = &jz4740_musb_ops; - - platform_set_drvdata(pdev, glue); - - ret = platform_device_add_resources(musb, pdev->resource, - pdev->num_resources); - if (ret) { - dev_err(&pdev->dev, "failed to add resources\n"); - goto err_clk_disable; - } - - ret = platform_device_add_data(musb, pdata, sizeof(*pdata)); - if (ret) { - dev_err(&pdev->dev, "failed to add platform_data\n"); - goto err_clk_disable; - } - - return 0; - -err_clk_disable: - clk_disable_unprepare(clk); -err_platform_device_put: - platform_device_put(musb); - return ret; -} - </programlisting> - <para> - The first step is to pass the device data privately held by the - glue layer on to the controller driver through - platform_set_drvdata() (line 7). Next is passing on the device - resources information, also privately held at that point, through - platform_device_add_resources() (line 9). - </para> - <para> - Finally comes passing on the platform specific data to the - controller driver (line 16). Platform data will be discussed in - <link linkend="device-platform-data">Chapter 4</link>, but here - we are looking at the platform_ops function pointer (line 5) in - musb_hdrc_platform_data structure (line 3). This function - pointer allows the MUSB controller driver to know which function - to call for device operation: - </para> - <programlisting linenumbering="numbered"> -static const struct musb_platform_ops jz4740_musb_ops = { - .init = jz4740_musb_init, - .exit = jz4740_musb_exit, -}; - </programlisting> - <para> - Here we have the minimal case where only init and exit functions - are called by the controller driver when needed. Fact is the - JZ4740 MUSB controller is a basic controller, lacking some - features found in other controllers, otherwise we may also have - pointers to a few other functions like a power management function - or a function to switch between OTG and non-OTG modes, for - instance. - </para> - <para> - At that point of the registration process, the controller driver - actually calls the init function: - </para> - <programlisting linenumbering="numbered"> -static int jz4740_musb_init(struct musb *musb) -{ - musb->xceiv = usb_get_phy(USB_PHY_TYPE_USB2); - if (!musb->xceiv) { - pr_err("HS UDC: no transceiver configured\n"); - return -ENODEV; - } - - /* Silicon does not implement ConfigData register. - * Set dyn_fifo to avoid reading EP config from hardware. - */ - musb->dyn_fifo = true; - - musb->isr = jz4740_musb_interrupt; - - return 0; -} - </programlisting> - <para> - The goal of jz4740_musb_init() is to get hold of the transceiver - driver data of the MUSB controller hardware and pass it on to the - MUSB controller driver, as usual. The transceiver is the circuitry - inside the controller hardware responsible for sending/receiving - the USB data. Since it is an implementation of the physical layer - of the OSI model, the transceiver is also referred to as PHY. - </para> - <para> - Getting hold of the MUSB PHY driver data is done with - usb_get_phy() which returns a pointer to the structure - containing the driver instance data. The next couple of - instructions (line 12 and 14) are used as a quirk and to setup - IRQ handling respectively. Quirks and IRQ handling will be - discussed later in <link linkend="device-quirks">Chapter - 5</link> and <link linkend="handling-irqs">Chapter 3</link>. - </para> - <programlisting linenumbering="numbered"> -static int jz4740_musb_exit(struct musb *musb) -{ - usb_put_phy(musb->xceiv); - - return 0; -} - </programlisting> - <para> - Acting as the counterpart of init, the exit function releases the - MUSB PHY driver when the controller hardware itself is about to be - released. - </para> - <para> - Again, note that init and exit are fairly simple in this case due - to the basic set of features of the JZ4740 controller hardware. - When writing an musb glue layer for a more complex controller - hardware, you might need to take care of more processing in those - two functions. - </para> - <para> - Returning from the init function, the MUSB controller driver jumps - back into the probe function: - </para> - <programlisting linenumbering="numbered"> -static int jz4740_probe(struct platform_device *pdev) -{ - ret = platform_device_add(musb); - if (ret) { - dev_err(&pdev->dev, "failed to register musb device\n"); - goto err_clk_disable; - } - - return 0; - -err_clk_disable: - clk_disable_unprepare(clk); -err_platform_device_put: - platform_device_put(musb); - return ret; -} - </programlisting> - <para> - This is the last part of the device registration process where the - glue layer adds the controller hardware device to Linux kernel - device hierarchy: at this stage, all known information about the - device is passed on to the Linux USB core stack. - </para> - <programlisting linenumbering="numbered"> -static int jz4740_remove(struct platform_device *pdev) -{ - struct jz4740_glue *glue = platform_get_drvdata(pdev); - - platform_device_unregister(glue->musb); - clk_disable_unprepare(glue->clk); - - return 0; -} - </programlisting> - <para> - Acting as the counterpart of probe, the remove function unregister - the MUSB controller hardware (line 5) and disable the clock (line - 6), allowing it to be gated. - </para> - </chapter> - - <chapter id="handling-irqs"> - <title>Handling IRQs</title> - <para> - Additionally to the MUSB controller hardware basic setup and - registration, the glue layer is also responsible for handling the - IRQs: - </para> - <programlisting linenumbering="numbered"> -static irqreturn_t jz4740_musb_interrupt(int irq, void *__hci) -{ - unsigned long flags; - irqreturn_t retval = IRQ_NONE; - struct musb *musb = __hci; - - spin_lock_irqsave(&musb->lock, flags); - - musb->int_usb = musb_readb(musb->mregs, MUSB_INTRUSB); - musb->int_tx = musb_readw(musb->mregs, MUSB_INTRTX); - musb->int_rx = musb_readw(musb->mregs, MUSB_INTRRX); - - /* - * The controller is gadget only, the state of the host mode IRQ bits is - * undefined. Mask them to make sure that the musb driver core will - * never see them set - */ - musb->int_usb &= MUSB_INTR_SUSPEND | MUSB_INTR_RESUME | - MUSB_INTR_RESET | MUSB_INTR_SOF; - - if (musb->int_usb || musb->int_tx || musb->int_rx) - retval = musb_interrupt(musb); - - spin_unlock_irqrestore(&musb->lock, flags); - - return retval; -} - </programlisting> - <para> - Here the glue layer mostly has to read the relevant hardware - registers and pass their values on to the controller driver which - will handle the actual event that triggered the IRQ. - </para> - <para> - The interrupt handler critical section is protected by the - spin_lock_irqsave() and counterpart spin_unlock_irqrestore() - functions (line 7 and 24 respectively), which prevent the - interrupt handler code to be run by two different threads at the - same time. - </para> - <para> - Then the relevant interrupt registers are read (line 9 to 11): - </para> - <itemizedlist> - <listitem> - <para> - MUSB_INTRUSB: indicates which USB interrupts are currently - active, - </para> - </listitem> - <listitem> - <para> - MUSB_INTRTX: indicates which of the interrupts for TX - endpoints are currently active, - </para> - </listitem> - <listitem> - <para> - MUSB_INTRRX: indicates which of the interrupts for TX - endpoints are currently active. - </para> - </listitem> - </itemizedlist> - <para> - Note that musb_readb() is used to read 8-bit registers at most, - while musb_readw() allows us to read at most 16-bit registers. - There are other functions that can be used depending on the size - of your device registers. See musb_io.h for more information. - </para> - <para> - Instruction on line 18 is another quirk specific to the JZ4740 - USB device controller, which will be discussed later in <link - linkend="device-quirks">Chapter 5</link>. - </para> - <para> - The glue layer still needs to register the IRQ handler though. - Remember the instruction on line 14 of the init function: - </para> - <programlisting linenumbering="numbered"> -static int jz4740_musb_init(struct musb *musb) -{ - musb->isr = jz4740_musb_interrupt; - - return 0; -} - </programlisting> - <para> - This instruction sets a pointer to the glue layer IRQ handler - function, in order for the controller hardware to call the handler - back when an IRQ comes from the controller hardware. The interrupt - handler is now implemented and registered. - </para> - </chapter> - - <chapter id="device-platform-data"> - <title>Device Platform Data</title> - <para> - In order to write an MUSB glue layer, you need to have some data - describing the hardware capabilities of your controller hardware, - which is called the platform data. - </para> - <para> - Platform data is specific to your hardware, though it may cover a - broad range of devices, and is generally found somewhere in the - arch/ directory, depending on your device architecture. - </para> - <para> - For instance, platform data for the JZ4740 SoC is found in - arch/mips/jz4740/platform.c. In the platform.c file each device of - the JZ4740 SoC is described through a set of structures. - </para> - <para> - Here is the part of arch/mips/jz4740/platform.c that covers the - USB Device Controller (UDC): - </para> - <programlisting linenumbering="numbered"> -/* USB Device Controller */ -struct platform_device jz4740_udc_xceiv_device = { - .name = "usb_phy_gen_xceiv", - .id = 0, -}; - -static struct resource jz4740_udc_resources[] = { - [0] = { - .start = JZ4740_UDC_BASE_ADDR, - .end = JZ4740_UDC_BASE_ADDR + 0x10000 - 1, - .flags = IORESOURCE_MEM, - }, - [1] = { - .start = JZ4740_IRQ_UDC, - .end = JZ4740_IRQ_UDC, - .flags = IORESOURCE_IRQ, - .name = "mc", - }, -}; - -struct platform_device jz4740_udc_device = { - .name = "musb-jz4740", - .id = -1, - .dev = { - .dma_mask = &jz4740_udc_device.dev.coherent_dma_mask, - .coherent_dma_mask = DMA_BIT_MASK(32), - }, - .num_resources = ARRAY_SIZE(jz4740_udc_resources), - .resource = jz4740_udc_resources, -}; - </programlisting> - <para> - The jz4740_udc_xceiv_device platform device structure (line 2) - describes the UDC transceiver with a name and id number. - </para> - <para> - At the time of this writing, note that - "usb_phy_gen_xceiv" is the specific name to be used for - all transceivers that are either built-in with reference USB IP or - autonomous and doesn't require any PHY programming. You will need - to set CONFIG_NOP_USB_XCEIV=y in the kernel configuration to make - use of the corresponding transceiver driver. The id field could be - set to -1 (equivalent to PLATFORM_DEVID_NONE), -2 (equivalent to - PLATFORM_DEVID_AUTO) or start with 0 for the first device of this - kind if we want a specific id number. - </para> - <para> - The jz4740_udc_resources resource structure (line 7) defines the - UDC registers base addresses. - </para> - <para> - The first array (line 9 to 11) defines the UDC registers base - memory addresses: start points to the first register memory - address, end points to the last register memory address and the - flags member defines the type of resource we are dealing with. So - IORESOURCE_MEM is used to define the registers memory addresses. - The second array (line 14 to 17) defines the UDC IRQ registers - addresses. Since there is only one IRQ register available for the - JZ4740 UDC, start and end point at the same address. The - IORESOURCE_IRQ flag tells that we are dealing with IRQ resources, - and the name "mc" is in fact hard-coded in the MUSB core - in order for the controller driver to retrieve this IRQ resource - by querying it by its name. - </para> - <para> - Finally, the jz4740_udc_device platform device structure (line 21) - describes the UDC itself. - </para> - <para> - The "musb-jz4740" name (line 22) defines the MUSB - driver that is used for this device; remember this is in fact - the name that we used in the jz4740_driver platform driver - structure in <link linkend="linux-musb-basics">Chapter - 2</link>. The id field (line 23) is set to -1 (equivalent to - PLATFORM_DEVID_NONE) since we do not need an id for the device: - the MUSB controller driver was already set to allocate an - automatic id in <link linkend="linux-musb-basics">Chapter - 2</link>. In the dev field we care for DMA related information - here. The dma_mask field (line 25) defines the width of the DMA - mask that is going to be used, and coherent_dma_mask (line 26) - has the same purpose but for the alloc_coherent DMA mappings: in - both cases we are using a 32 bits mask. Then the resource field - (line 29) is simply a pointer to the resource structure defined - before, while the num_resources field (line 28) keeps track of - the number of arrays defined in the resource structure (in this - case there were two resource arrays defined before). - </para> - <para> - With this quick overview of the UDC platform data at the arch/ - level now done, let's get back to the MUSB glue layer specific - platform data in drivers/usb/musb/jz4740.c: - </para> - <programlisting linenumbering="numbered"> -static struct musb_hdrc_config jz4740_musb_config = { - /* Silicon does not implement USB OTG. */ - .multipoint = 0, - /* Max EPs scanned, driver will decide which EP can be used. */ - .num_eps = 4, - /* RAMbits needed to configure EPs from table */ - .ram_bits = 9, - .fifo_cfg = jz4740_musb_fifo_cfg, - .fifo_cfg_size = ARRAY_SIZE(jz4740_musb_fifo_cfg), -}; - -static struct musb_hdrc_platform_data jz4740_musb_platform_data = { - .mode = MUSB_PERIPHERAL, - .config = &jz4740_musb_config, -}; - </programlisting> - <para> - First the glue layer configures some aspects of the controller - driver operation related to the controller hardware specifics. - This is done through the jz4740_musb_config musb_hdrc_config - structure. - </para> - <para> - Defining the OTG capability of the controller hardware, the - multipoint member (line 3) is set to 0 (equivalent to false) - since the JZ4740 UDC is not OTG compatible. Then num_eps (line - 5) defines the number of USB endpoints of the controller - hardware, including endpoint 0: here we have 3 endpoints + - endpoint 0. Next is ram_bits (line 7) which is the width of the - RAM address bus for the MUSB controller hardware. This - information is needed when the controller driver cannot - automatically configure endpoints by reading the relevant - controller hardware registers. This issue will be discussed when - we get to device quirks in <link linkend="device-quirks">Chapter - 5</link>. Last two fields (line 8 and 9) are also about device - quirks: fifo_cfg points to the USB endpoints configuration table - and fifo_cfg_size keeps track of the size of the number of - entries in that configuration table. More on that later in <link - linkend="device-quirks">Chapter 5</link>. - </para> - <para> - Then this configuration is embedded inside - jz4740_musb_platform_data musb_hdrc_platform_data structure (line - 11): config is a pointer to the configuration structure itself, - and mode tells the controller driver if the controller hardware - may be used as MUSB_HOST only, MUSB_PERIPHERAL only or MUSB_OTG - which is a dual mode. - </para> - <para> - Remember that jz4740_musb_platform_data is then used to convey - platform data information as we have seen in the probe function - in <link linkend="linux-musb-basics">Chapter 2</link> - </para> - </chapter> - - <chapter id="device-quirks"> - <title>Device Quirks</title> - <para> - Completing the platform data specific to your device, you may also - need to write some code in the glue layer to work around some - device specific limitations. These quirks may be due to some - hardware bugs, or simply be the result of an incomplete - implementation of the USB On-the-Go specification. - </para> - <para> - The JZ4740 UDC exhibits such quirks, some of which we will discuss - here for the sake of insight even though these might not be found - in the controller hardware you are working on. - </para> - <para> - Let's get back to the init function first: - </para> - <programlisting linenumbering="numbered"> -static int jz4740_musb_init(struct musb *musb) -{ - musb->xceiv = usb_get_phy(USB_PHY_TYPE_USB2); - if (!musb->xceiv) { - pr_err("HS UDC: no transceiver configured\n"); - return -ENODEV; - } - - /* Silicon does not implement ConfigData register. - * Set dyn_fifo to avoid reading EP config from hardware. - */ - musb->dyn_fifo = true; - - musb->isr = jz4740_musb_interrupt; - - return 0; -} - </programlisting> - <para> - Instruction on line 12 helps the MUSB controller driver to work - around the fact that the controller hardware is missing registers - that are used for USB endpoints configuration. - </para> - <para> - Without these registers, the controller driver is unable to read - the endpoints configuration from the hardware, so we use line 12 - instruction to bypass reading the configuration from silicon, and - rely on a hard-coded table that describes the endpoints - configuration instead: - </para> - <programlisting linenumbering="numbered"> -static struct musb_fifo_cfg jz4740_musb_fifo_cfg[] = { -{ .hw_ep_num = 1, .style = FIFO_TX, .maxpacket = 512, }, -{ .hw_ep_num = 1, .style = FIFO_RX, .maxpacket = 512, }, -{ .hw_ep_num = 2, .style = FIFO_TX, .maxpacket = 64, }, -}; - </programlisting> - <para> - Looking at the configuration table above, we see that each - endpoints is described by three fields: hw_ep_num is the endpoint - number, style is its direction (either FIFO_TX for the controller - driver to send packets in the controller hardware, or FIFO_RX to - receive packets from hardware), and maxpacket defines the maximum - size of each data packet that can be transmitted over that - endpoint. Reading from the table, the controller driver knows that - endpoint 1 can be used to send and receive USB data packets of 512 - bytes at once (this is in fact a bulk in/out endpoint), and - endpoint 2 can be used to send data packets of 64 bytes at once - (this is in fact an interrupt endpoint). - </para> - <para> - Note that there is no information about endpoint 0 here: that one - is implemented by default in every silicon design, with a - predefined configuration according to the USB specification. For - more examples of endpoint configuration tables, see musb_core.c. - </para> - <para> - Let's now get back to the interrupt handler function: - </para> - <programlisting linenumbering="numbered"> -static irqreturn_t jz4740_musb_interrupt(int irq, void *__hci) -{ - unsigned long flags; - irqreturn_t retval = IRQ_NONE; - struct musb *musb = __hci; - - spin_lock_irqsave(&musb->lock, flags); - - musb->int_usb = musb_readb(musb->mregs, MUSB_INTRUSB); - musb->int_tx = musb_readw(musb->mregs, MUSB_INTRTX); - musb->int_rx = musb_readw(musb->mregs, MUSB_INTRRX); - - /* - * The controller is gadget only, the state of the host mode IRQ bits is - * undefined. Mask them to make sure that the musb driver core will - * never see them set - */ - musb->int_usb &= MUSB_INTR_SUSPEND | MUSB_INTR_RESUME | - MUSB_INTR_RESET | MUSB_INTR_SOF; - - if (musb->int_usb || musb->int_tx || musb->int_rx) - retval = musb_interrupt(musb); - - spin_unlock_irqrestore(&musb->lock, flags); - - return retval; -} - </programlisting> - <para> - Instruction on line 18 above is a way for the controller driver to - work around the fact that some interrupt bits used for USB host - mode operation are missing in the MUSB_INTRUSB register, thus left - in an undefined hardware state, since this MUSB controller - hardware is used in peripheral mode only. As a consequence, the - glue layer masks these missing bits out to avoid parasite - interrupts by doing a logical AND operation between the value read - from MUSB_INTRUSB and the bits that are actually implemented in - the register. - </para> - <para> - These are only a couple of the quirks found in the JZ4740 USB - device controller. Some others were directly addressed in the MUSB - core since the fixes were generic enough to provide a better - handling of the issues for others controller hardware eventually. - </para> - </chapter> - - <chapter id="conclusion"> - <title>Conclusion</title> - <para> - Writing a Linux MUSB glue layer should be a more accessible task, - as this documentation tries to show the ins and outs of this - exercise. - </para> - <para> - The JZ4740 USB device controller being fairly simple, I hope its - glue layer serves as a good example for the curious mind. Used - with the current MUSB glue layers, this documentation should - provide enough guidance to get started; should anything gets out - of hand, the linux-usb mailing list archive is another helpful - resource to browse through. - </para> - </chapter> - - <chapter id="acknowledgements"> - <title>Acknowledgements</title> - <para> - Many thanks to Lars-Peter Clausen and Maarten ter Huurne for - answering my questions while I was writing the JZ4740 glue layer - and for helping me out getting the code in good shape. - </para> - <para> - I would also like to thank the Qi-Hardware community at large for - its cheerful guidance and support. - </para> - </chapter> - - <chapter id="resources"> - <title>Resources</title> - <para> - USB Home Page: - <ulink url="http://www.usb.org">http://www.usb.org</ulink> - </para> - <para> - linux-usb Mailing List Archives: - <ulink url="http://marc.info/?l=linux-usb">http://marc.info/?l=linux-usb</ulink> - </para> - <para> - USB On-the-Go Basics: - <ulink url="http://www.maximintegrated.com/app-notes/index.mvp/id/1822">http://www.maximintegrated.com/app-notes/index.mvp/id/1822</ulink> - </para> - <para> - Writing USB Device Drivers: - <ulink url="https://www.kernel.org/doc/htmldocs/writing_usb_driver/index.html">https://www.kernel.org/doc/htmldocs/writing_usb_driver/index.html</ulink> - </para> - <para> - Texas Instruments USB Configuration Wiki Page: - <ulink url="http://processors.wiki.ti.com/index.php/Usbgeneralpage">http://processors.wiki.ti.com/index.php/Usbgeneralpage</ulink> - </para> - <para> - Analog Devices Blackfin MUSB Configuration: - <ulink url="http://docs.blackfin.uclinux.org/doku.php?id=linux-kernel:drivers:musb">http://docs.blackfin.uclinux.org/doku.php?id=linux-kernel:drivers:musb</ulink> - </para> - </chapter> - -</book> diff --git a/Documentation/DocBook/writing_usb_driver.tmpl b/Documentation/DocBook/writing_usb_driver.tmpl deleted file mode 100644 index 3210dcf741c9..000000000000 --- a/Documentation/DocBook/writing_usb_driver.tmpl +++ /dev/null @@ -1,412 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> - -<book id="USBDeviceDriver"> - <bookinfo> - <title>Writing USB Device Drivers</title> - - <authorgroup> - <author> - <firstname>Greg</firstname> - <surname>Kroah-Hartman</surname> - <affiliation> - <address> - <email>greg@kroah.com</email> - </address> - </affiliation> - </author> - </authorgroup> - - <copyright> - <year>2001-2002</year> - <holder>Greg Kroah-Hartman</holder> - </copyright> - - <legalnotice> - <para> - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later - version. - </para> - - <para> - This program is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - </para> - - <para> - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - </para> - - <para> - For more details see the file COPYING in the source - distribution of Linux. - </para> - - <para> - This documentation is based on an article published in - Linux Journal Magazine, October 2001, Issue 90. - </para> - </legalnotice> - </bookinfo> - -<toc></toc> - - <chapter id="intro"> - <title>Introduction</title> - <para> - The Linux USB subsystem has grown from supporting only two different - types of devices in the 2.2.7 kernel (mice and keyboards), to over 20 - different types of devices in the 2.4 kernel. Linux currently supports - almost all USB class devices (standard types of devices like keyboards, - mice, modems, printers and speakers) and an ever-growing number of - vendor-specific devices (such as USB to serial converters, digital - cameras, Ethernet devices and MP3 players). For a full list of the - different USB devices currently supported, see Resources. - </para> - <para> - The remaining kinds of USB devices that do not have support on Linux are - almost all vendor-specific devices. Each vendor decides to implement a - custom protocol to talk to their device, so a custom driver usually needs - to be created. Some vendors are open with their USB protocols and help - with the creation of Linux drivers, while others do not publish them, and - developers are forced to reverse-engineer. See Resources for some links - to handy reverse-engineering tools. - </para> - <para> - Because each different protocol causes a new driver to be created, I have - written a generic USB driver skeleton, modelled after the pci-skeleton.c - file in the kernel source tree upon which many PCI network drivers have - been based. This USB skeleton can be found at drivers/usb/usb-skeleton.c - in the kernel source tree. In this article I will walk through the basics - of the skeleton driver, explaining the different pieces and what needs to - be done to customize it to your specific device. - </para> - </chapter> - - <chapter id="basics"> - <title>Linux USB Basics</title> - <para> - If you are going to write a Linux USB driver, please become familiar with - the USB protocol specification. It can be found, along with many other - useful documents, at the USB home page (see Resources). An excellent - introduction to the Linux USB subsystem can be found at the USB Working - Devices List (see Resources). It explains how the Linux USB subsystem is - structured and introduces the reader to the concept of USB urbs - (USB Request Blocks), which are essential to USB drivers. - </para> - <para> - The first thing a Linux USB driver needs to do is register itself with - the Linux USB subsystem, giving it some information about which devices - the driver supports and which functions to call when a device supported - by the driver is inserted or removed from the system. All of this - information is passed to the USB subsystem in the usb_driver structure. - The skeleton driver declares a usb_driver as: - </para> - <programlisting> -static struct usb_driver skel_driver = { - .name = "skeleton", - .probe = skel_probe, - .disconnect = skel_disconnect, - .fops = &skel_fops, - .minor = USB_SKEL_MINOR_BASE, - .id_table = skel_table, -}; - </programlisting> - <para> - The variable name is a string that describes the driver. It is used in - informational messages printed to the system log. The probe and - disconnect function pointers are called when a device that matches the - information provided in the id_table variable is either seen or removed. - </para> - <para> - The fops and minor variables are optional. Most USB drivers hook into - another kernel subsystem, such as the SCSI, network or TTY subsystem. - These types of drivers register themselves with the other kernel - subsystem, and any user-space interactions are provided through that - interface. But for drivers that do not have a matching kernel subsystem, - such as MP3 players or scanners, a method of interacting with user space - is needed. The USB subsystem provides a way to register a minor device - number and a set of file_operations function pointers that enable this - user-space interaction. The skeleton driver needs this kind of interface, - so it provides a minor starting number and a pointer to its - file_operations functions. - </para> - <para> - The USB driver is then registered with a call to usb_register, usually in - the driver's init function, as shown here: - </para> - <programlisting> -static int __init usb_skel_init(void) -{ - int result; - - /* register this driver with the USB subsystem */ - result = usb_register(&skel_driver); - if (result < 0) { - err("usb_register failed for the "__FILE__ "driver." - "Error number %d", result); - return -1; - } - - return 0; -} -module_init(usb_skel_init); - </programlisting> - <para> - When the driver is unloaded from the system, it needs to deregister - itself with the USB subsystem. This is done with the usb_deregister - function: - </para> - <programlisting> -static void __exit usb_skel_exit(void) -{ - /* deregister this driver with the USB subsystem */ - usb_deregister(&skel_driver); -} -module_exit(usb_skel_exit); - </programlisting> - <para> - To enable the linux-hotplug system to load the driver automatically when - the device is plugged in, you need to create a MODULE_DEVICE_TABLE. The - following code tells the hotplug scripts that this module supports a - single device with a specific vendor and product ID: - </para> - <programlisting> -/* table of devices that work with this driver */ -static struct usb_device_id skel_table [] = { - { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) }, - { } /* Terminating entry */ -}; -MODULE_DEVICE_TABLE (usb, skel_table); - </programlisting> - <para> - There are other macros that can be used in describing a usb_device_id for - drivers that support a whole class of USB drivers. See usb.h for more - information on this. - </para> - </chapter> - - <chapter id="device"> - <title>Device operation</title> - <para> - When a device is plugged into the USB bus that matches the device ID - pattern that your driver registered with the USB core, the probe function - is called. The usb_device structure, interface number and the interface ID - are passed to the function: - </para> - <programlisting> -static int skel_probe(struct usb_interface *interface, - const struct usb_device_id *id) - </programlisting> - <para> - The driver now needs to verify that this device is actually one that it - can accept. If so, it returns 0. - If not, or if any error occurs during initialization, an errorcode - (such as <literal>-ENOMEM</literal> or <literal>-ENODEV</literal>) - is returned from the probe function. - </para> - <para> - In the skeleton driver, we determine what end points are marked as bulk-in - and bulk-out. We create buffers to hold the data that will be sent and - received from the device, and a USB urb to write data to the device is - initialized. - </para> - <para> - Conversely, when the device is removed from the USB bus, the disconnect - function is called with the device pointer. The driver needs to clean any - private data that has been allocated at this time and to shut down any - pending urbs that are in the USB system. - </para> - <para> - Now that the device is plugged into the system and the driver is bound to - the device, any of the functions in the file_operations structure that - were passed to the USB subsystem will be called from a user program trying - to talk to the device. The first function called will be open, as the - program tries to open the device for I/O. We increment our private usage - count and save a pointer to our internal structure in the file - structure. This is done so that future calls to file operations will - enable the driver to determine which device the user is addressing. All - of this is done with the following code: - </para> - <programlisting> -/* increment our usage count for the module */ -++skel->open_count; - -/* save our object in the file's private structure */ -file->private_data = dev; - </programlisting> - <para> - After the open function is called, the read and write functions are called - to receive and send data to the device. In the skel_write function, we - receive a pointer to some data that the user wants to send to the device - and the size of the data. The function determines how much data it can - send to the device based on the size of the write urb it has created (this - size depends on the size of the bulk out end point that the device has). - Then it copies the data from user space to kernel space, points the urb to - the data and submits the urb to the USB subsystem. This can be seen in - the following code: - </para> - <programlisting> -/* we can only write as much as 1 urb will hold */ -bytes_written = (count > skel->bulk_out_size) ? skel->bulk_out_size : count; - -/* copy the data from user space into our urb */ -copy_from_user(skel->write_urb->transfer_buffer, buffer, bytes_written); - -/* set up our urb */ -usb_fill_bulk_urb(skel->write_urb, - skel->dev, - usb_sndbulkpipe(skel->dev, skel->bulk_out_endpointAddr), - skel->write_urb->transfer_buffer, - bytes_written, - skel_write_bulk_callback, - skel); - -/* send the data out the bulk port */ -result = usb_submit_urb(skel->write_urb); -if (result) { - err("Failed submitting write urb, error %d", result); -} - </programlisting> - <para> - When the write urb is filled up with the proper information using the - usb_fill_bulk_urb function, we point the urb's completion callback to call our - own skel_write_bulk_callback function. This function is called when the - urb is finished by the USB subsystem. The callback function is called in - interrupt context, so caution must be taken not to do very much processing - at that time. Our implementation of skel_write_bulk_callback merely - reports if the urb was completed successfully or not and then returns. - </para> - <para> - The read function works a bit differently from the write function in that - we do not use an urb to transfer data from the device to the driver. - Instead we call the usb_bulk_msg function, which can be used to send or - receive data from a device without having to create urbs and handle - urb completion callback functions. We call the usb_bulk_msg function, - giving it a buffer into which to place any data received from the device - and a timeout value. If the timeout period expires without receiving any - data from the device, the function will fail and return an error message. - This can be shown with the following code: - </para> - <programlisting> -/* do an immediate bulk read to get data from the device */ -retval = usb_bulk_msg (skel->dev, - usb_rcvbulkpipe (skel->dev, - skel->bulk_in_endpointAddr), - skel->bulk_in_buffer, - skel->bulk_in_size, - &count, HZ*10); -/* if the read was successful, copy the data to user space */ -if (!retval) { - if (copy_to_user (buffer, skel->bulk_in_buffer, count)) - retval = -EFAULT; - else - retval = count; -} - </programlisting> - <para> - The usb_bulk_msg function can be very useful for doing single reads or - writes to a device; however, if you need to read or write constantly to a - device, it is recommended to set up your own urbs and submit them to the - USB subsystem. - </para> - <para> - When the user program releases the file handle that it has been using to - talk to the device, the release function in the driver is called. In this - function we decrement our private usage count and wait for possible - pending writes: - </para> - <programlisting> -/* decrement our usage count for the device */ ---skel->open_count; - </programlisting> - <para> - One of the more difficult problems that USB drivers must be able to handle - smoothly is the fact that the USB device may be removed from the system at - any point in time, even if a program is currently talking to it. It needs - to be able to shut down any current reads and writes and notify the - user-space programs that the device is no longer there. The following - code (function <function>skel_delete</function>) - is an example of how to do this: </para> - <programlisting> -static inline void skel_delete (struct usb_skel *dev) -{ - kfree (dev->bulk_in_buffer); - if (dev->bulk_out_buffer != NULL) - usb_free_coherent (dev->udev, dev->bulk_out_size, - dev->bulk_out_buffer, - dev->write_urb->transfer_dma); - usb_free_urb (dev->write_urb); - kfree (dev); -} - </programlisting> - <para> - If a program currently has an open handle to the device, we reset the flag - <literal>device_present</literal>. For - every read, write, release and other functions that expect a device to be - present, the driver first checks this flag to see if the device is - still present. If not, it releases that the device has disappeared, and a - -ENODEV error is returned to the user-space program. When the release - function is eventually called, it determines if there is no device - and if not, it does the cleanup that the skel_disconnect - function normally does if there are no open files on the device (see - Listing 5). - </para> - </chapter> - - <chapter id="iso"> - <title>Isochronous Data</title> - <para> - This usb-skeleton driver does not have any examples of interrupt or - isochronous data being sent to or from the device. Interrupt data is sent - almost exactly as bulk data is, with a few minor exceptions. Isochronous - data works differently with continuous streams of data being sent to or - from the device. The audio and video camera drivers are very good examples - of drivers that handle isochronous data and will be useful if you also - need to do this. - </para> - </chapter> - - <chapter id="Conclusion"> - <title>Conclusion</title> - <para> - Writing Linux USB device drivers is not a difficult task as the - usb-skeleton driver shows. This driver, combined with the other current - USB drivers, should provide enough examples to help a beginning author - create a working driver in a minimal amount of time. The linux-usb-devel - mailing list archives also contain a lot of helpful information. - </para> - </chapter> - - <chapter id="resources"> - <title>Resources</title> - <para> - The Linux USB Project: <ulink url="http://www.linux-usb.org">http://www.linux-usb.org/</ulink> - </para> - <para> - Linux Hotplug Project: <ulink url="http://linux-hotplug.sourceforge.net">http://linux-hotplug.sourceforge.net/</ulink> - </para> - <para> - Linux USB Working Devices List: <ulink url="http://www.qbik.ch/usb/devices">http://www.qbik.ch/usb/devices/</ulink> - </para> - <para> - linux-usb-devel Mailing List Archives: <ulink url="http://marc.theaimsgroup.com/?l=linux-usb-devel">http://marc.theaimsgroup.com/?l=linux-usb-devel</ulink> - </para> - <para> - Programming Guide for Linux USB Device Drivers: <ulink url="http://usb.cs.tum.edu/usbdoc">http://usb.cs.tum.edu/usbdoc</ulink> - </para> - <para> - USB Home Page: <ulink url="http://www.usb.org">http://www.usb.org</ulink> - </para> - </chapter> - -</book> |