| .. 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/ |
