net: wwan: t7xx: Add maintainers and documentation

Adds maintainers and documentation for MediaTek t7xx 5G WWAN modem
device driver.

Signed-off-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 121 insertions, 0 deletions

diff --git a/Documentation/networking/device_drivers/wwan/index.rst b/Documentation/networking/device_drivers/wwan/index.rst
index 1cb8c7371401..370d8264d5dc 100644
--- a/Documentation/networking/device_drivers/wwan/index.rst
+++ b/Documentation/networking/device_drivers/wwan/index.rst
@@ -9,6 +9,7 @@ Contents:
    :maxdepth: 2
 
    iosm
+   t7xx
 
 .. only::  subproject and html
 
diff --git a/Documentation/networking/device_drivers/wwan/t7xx.rst b/Documentation/networking/device_drivers/wwan/t7xx.rst
new file mode 100644
index 000000000000..dd5b731957ca
--- /dev/null
+++ b/Documentation/networking/device_drivers/wwan/t7xx.rst
@@ -0,0 +1,120 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+.. Copyright (C) 2020-21 Intel Corporation
+
+.. _t7xx_driver_doc:
+
+============================================
+t7xx driver for MTK PCIe based T700 5G modem
+============================================
+The t7xx driver is a WWAN PCIe host driver developed for linux or Chrome OS platforms
+for data exchange over PCIe interface between Host platform & MediaTek's T700 5G modem.
+The driver exposes an interface conforming to the MBIM protocol [1]. Any front end
+application (e.g. Modem Manager) could easily manage the MBIM interface to enable
+data communication towards WWAN. The driver also provides an interface to interact
+with the MediaTek's modem via AT commands.
+
+Basic usage
+===========
+MBIM & AT functions are inactive when unmanaged. The t7xx driver provides
+WWAN port userspace interfaces representing MBIM & AT control channels and does
+not play any role in managing their functionality. It is the job of a userspace
+application to detect port enumeration and enable MBIM & AT functionalities.
+
+Examples of few such userspace applications 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 Applications to carry out below required actions for send an AT
+command and receive response:
+
+- open the AT control channel using a UART tool or a special user tool
+
+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 t7xx 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 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 wwan0 type wwan linkid 1
+
+The driver will automatically map the "wwan0-1" network device to MBIM IP
+session 1.
+
+AT port userspace ABI
+----------------------------------
+
+/dev/wwan0at0 character device
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The driver exposes an AT port by implementing AT WWAN Port.
+The userspace end of the control port is a /dev/wwan0at0 character
+device. Application shall use this interface to issue AT commands.
+
+The MediaTek's T700 modem supports the 3GPP TS 27.007 [4] specification.
+
+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/5G) devices and connections"*
+
+- http://www.freedesktop.org/wiki/Software/ModemManager/
+
+[4] *Specification # 27.007 - 3GPP*
+
+- https://www.3gpp.org/DynaReport/27007.htm