Documentation/networking/device_drivers/wwan/iosm.rst

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Documentation/networking/device_drivers/wwan/iosm.rst
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.. 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

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