diff options
Diffstat (limited to 'Documentation/usb')
| -rw-r--r-- | Documentation/usb/dma.txt | 6 | ||||
| -rw-r--r-- | Documentation/usb/dwc3.txt | 45 | ||||
| -rw-r--r-- | Documentation/usb/power-management.txt | 26 |
3 files changed, 74 insertions, 3 deletions
diff --git a/Documentation/usb/dma.txt b/Documentation/usb/dma.txt index 84ef865237db..444651e70d95 100644 --- a/Documentation/usb/dma.txt +++ b/Documentation/usb/dma.txt @@ -7,7 +7,7 @@ API OVERVIEW The big picture is that USB drivers can continue to ignore most DMA issues, though they still must provide DMA-ready buffers (see -Documentation/PCI/PCI-DMA-mapping.txt). That's how they've worked through +Documentation/DMA-API-HOWTO.txt). That's how they've worked through the 2.4 (and earlier) kernels. OR: they can now be DMA-aware. @@ -57,7 +57,7 @@ and effects like cache-trashing can impose subtle penalties. force a consistent memory access ordering by using memory barriers. It's not using a streaming DMA mapping, so it's good for small transfers on systems where the I/O would otherwise thrash an IOMMU mapping. (See - Documentation/PCI/PCI-DMA-mapping.txt for definitions of "coherent" and + Documentation/DMA-API-HOWTO.txt for definitions of "coherent" and "streaming" DMA mappings.) Asking for 1/Nth of a page (as well as asking for N pages) is reasonably @@ -88,7 +88,7 @@ WORKING WITH EXISTING BUFFERS Existing buffers aren't usable for DMA without first being mapped into the DMA address space of the device. However, most buffers passed to your driver can safely be used with such DMA mapping. (See the first section -of Documentation/PCI/PCI-DMA-mapping.txt, titled "What memory is DMA-able?") +of Documentation/DMA-API-HOWTO.txt, titled "What memory is DMA-able?") - When you're using scatterlists, you can map everything at once. On some systems, this kicks in an IOMMU and turns the scatterlists into single diff --git a/Documentation/usb/dwc3.txt b/Documentation/usb/dwc3.txt new file mode 100644 index 000000000000..7b590edae145 --- /dev/null +++ b/Documentation/usb/dwc3.txt @@ -0,0 +1,45 @@ + + TODO +~~~~~~ +Please pick something while reading :) + +- Convert interrupt handler to per-ep-thread-irq + + As it turns out some DWC3-commands ~1ms to complete. Currently we spin + until the command completes which is bad. + + Implementation idea: + - dwc core implements a demultiplexing irq chip for interrupts per + endpoint. The interrupt numbers are allocated during probe and belong + to the device. If MSI provides per-endpoint interrupt this dummy + interrupt chip can be replaced with "real" interrupts. + - interrupts are requested / allocated on usb_ep_enable() and removed on + usb_ep_disable(). Worst case are 32 interrupts, the lower limit is two + for ep0/1. + - dwc3_send_gadget_ep_cmd() will sleep in wait_for_completion_timeout() + until the command completes. + - the interrupt handler is split into the following pieces: + - primary handler of the device + goes through every event and calls generic_handle_irq() for event + it. On return from generic_handle_irq() in acknowledges the event + counter so interrupt goes away (eventually). + + - threaded handler of the device + none + + - primary handler of the EP-interrupt + reads the event and tries to process it. Everything that requries + sleeping is handed over to the Thread. The event is saved in an + per-endpoint data-structure. + We probably have to pay attention not to process events once we + handed something to thread so we don't process event X prio Y + where X > Y. + + - threaded handler of the EP-interrupt + handles the remaining EP work which might sleep such as waiting + for command completion. + + Latency: + There should be no increase in latency since the interrupt-thread has a + high priority and will be run before an average task in user land + (except the user changed priorities). diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt index e8662a5fbc5d..12511c98cc4f 100644 --- a/Documentation/usb/power-management.txt +++ b/Documentation/usb/power-management.txt @@ -487,3 +487,29 @@ succeed, it may still remain active and thus cause the system to resume as soon as the system suspend is complete. Or the remote wakeup may fail and get lost. Which outcome occurs depends on timing and on the hardware and firmware design. + + + xHCI hardware link PM + --------------------- + +xHCI host controller provides hardware link power management to usb2.0 +(xHCI 1.0 feature) and usb3.0 devices which support link PM. By +enabling hardware LPM, the host can automatically put the device into +lower power state(L1 for usb2.0 devices, or U1/U2 for usb3.0 devices), +which state device can enter and resume very quickly. + +The user interface for controlling USB2 hardware LPM is located in the +power/ subdirectory of each USB device's sysfs directory, that is, in +/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The +relevant attribute files is usb2_hardware_lpm. + + power/usb2_hardware_lpm + + When a USB2 device which support LPM is plugged to a + xHCI host root hub which support software LPM, the + host will run a software LPM test for it; if the device + enters L1 state and resume successfully and the host + supports USB2 hardware LPM, this file will show up and + driver will enable hardware LPM for the device. You + can write y/Y/1 or n/N/0 to the file to enable/disable + USB2 hardware LPM manually. This is for test purpose mainly. |