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diff --git a/Documentation/networking/device_drivers/wwan/iosm.rst b/Documentation/networking/device_drivers/wwan/iosm.rst new file mode 100644 index 000000000000..aceb0223eb46 --- /dev/null +++ b/Documentation/networking/device_drivers/wwan/iosm.rst @@ -0,0 +1,96 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +.. Copyright (C) 2020-21 Intel Corporation + +.. _iosm_driver_doc: + +=========================================== +IOSM Driver for Intel M.2 PCIe based Modems +=========================================== +The IOSM (IPC over Shared Memory) driver is a WWAN PCIe host driver developed +for linux or chrome platform for data exchange over PCIe interface between +Host platform & Intel M.2 Modem. The driver exposes interface conforming to the +MBIM protocol [1]. Any front end application ( eg: Modem Manager) could easily +manage the MBIM interface to enable data communication towards WWAN. + +Basic usage +=========== +MBIM functions are inactive when unmanaged. The IOSM driver only provides a +userspace interface MBIM "WWAN PORT" representing MBIM control channel and does +not play any role in managing the functionality. It is the job of a userspace +application to detect port enumeration and enable MBIM functionality. + +Examples of few such userspace application are: +- mbimcli (included with the libmbim [2] library), and +- Modem Manager [3] + +Management Applications to carry out below required actions for establishing +MBIM IP session: +- open the MBIM control channel +- configure network connection settings +- connect to network +- configure IP network interface + +Management application development +================================== +The driver and userspace interfaces are described below. The MBIM protocol is +described in [1] Mobile Broadband Interface Model v1.0 Errata-1. + +MBIM control channel userspace ABI +---------------------------------- + +/dev/wwan0mbim0 character device +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The driver exposes an MBIM interface to the MBIM function by implementing +MBIM WWAN Port. The userspace end of the control channel pipe is a +/dev/wwan0mbim0 character device. Application shall use this interface for +MBIM protocol communication. + +Fragmentation +~~~~~~~~~~~~~ +The userspace application is responsible for all control message fragmentation +and defragmentation as per MBIM specification. + +/dev/wwan0mbim0 write() +~~~~~~~~~~~~~~~~~~~~~~~ +The MBIM control messages from the management application must not exceed the +negotiated control message size. + +/dev/wwan0mbim0 read() +~~~~~~~~~~~~~~~~~~~~~~ +The management application must accept control messages of up the negotiated +control message size. + +MBIM data channel userspace ABI +------------------------------- + +wwan0-X network device +~~~~~~~~~~~~~~~~~~~~~~ +The IOSM driver exposes IP link interface "wwan0-X" of type "wwan" for IP +traffic. Iproute network utility is used for creating "wwan0-X" network +interface and for associating it with MBIM IP session. The Driver supports +upto 8 IP sessions for simultaneous IP communication. + +The userspace management application is responsible for creating new IP link +prior to establishing MBIM IP session where the SessionId is greater than 0. + +For example, creating new IP link for a MBIM IP session with SessionId 1: + + ip link add dev wwan0-1 parentdev-name wwan0 type wwan linkid 1 + +The driver will automatically map the "wwan0-1" network device to MBIM IP +session 1. + +References +========== +[1] "MBIM (Mobile Broadband Interface Model) Errata-1" + - https://www.usb.org/document-library/ + +[2] libmbim - "a glib-based library for talking to WWAN modems and + devices which speak the Mobile Interface Broadband Model (MBIM) + protocol" + - http://www.freedesktop.org/wiki/Software/libmbim/ + +[3] Modem Manager - "a DBus-activated daemon which controls mobile + broadband (2G/3G/4G) devices and connections" + - http://www.freedesktop.org/wiki/Software/ModemManager/ |