1.. SPDX-License-Identifier: GPL-2.0-only
2
3.. Copyright (C) 2020-21 Intel Corporation
4
5.. _t7xx_driver_doc:
6
7============================================
8t7xx driver for MTK PCIe based T700 5G modem
9============================================
10The t7xx driver is a WWAN PCIe host driver developed for linux or Chrome OS platforms
11for data exchange over PCIe interface between Host platform & MediaTek's T700 5G modem.
12The driver exposes an interface conforming to the MBIM protocol [1]. Any front end
13application (e.g. Modem Manager) could easily manage the MBIM interface to enable
14data communication towards WWAN. The driver also provides an interface to interact
15with the MediaTek's modem via AT commands.
16
17Basic usage
18===========
19MBIM & AT functions are inactive when unmanaged. The t7xx driver provides
20WWAN port userspace interfaces representing MBIM & AT control channels and does
21not play any role in managing their functionality. It is the job of a userspace
22application to detect port enumeration and enable MBIM & AT functionalities.
23
24Examples of few such userspace applications are:
25
26- mbimcli (included with the libmbim [2] library), and
27- Modem Manager [3]
28
29Management Applications to carry out below required actions for establishing
30MBIM IP session:
31
32- open the MBIM control channel
33- configure network connection settings
34- connect to network
35- configure IP network interface
36
37Management Applications to carry out below required actions for send an AT
38command and receive response:
39
40- open the AT control channel using a UART tool or a special user tool
41
42Management application development
43==================================
44The driver and userspace interfaces are described below. The MBIM protocol is
45described in [1] Mobile Broadband Interface Model v1.0 Errata-1.
46
47MBIM control channel userspace ABI
48----------------------------------
49
50/dev/wwan0mbim0 character device
51~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
52The driver exposes an MBIM interface to the MBIM function by implementing
53MBIM WWAN Port. The userspace end of the control channel pipe is a
54/dev/wwan0mbim0 character device. Application shall use this interface for
55MBIM protocol communication.
56
57Fragmentation
58~~~~~~~~~~~~~
59The userspace application is responsible for all control message fragmentation
60and defragmentation as per MBIM specification.
61
62/dev/wwan0mbim0 write()
63~~~~~~~~~~~~~~~~~~~~~~~
64The MBIM control messages from the management application must not exceed the
65negotiated control message size.
66
67/dev/wwan0mbim0 read()
68~~~~~~~~~~~~~~~~~~~~~~
69The management application must accept control messages of up the negotiated
70control message size.
71
72MBIM data channel userspace ABI
73-------------------------------
74
75wwan0-X network device
76~~~~~~~~~~~~~~~~~~~~~~
77The t7xx driver exposes IP link interface "wwan0-X" of type "wwan" for IP
78traffic. Iproute network utility is used for creating "wwan0-X" network
79interface and for associating it with MBIM IP session.
80
81The userspace management application is responsible for creating new IP link
82prior to establishing MBIM IP session where the SessionId is greater than 0.
83
84For example, creating new IP link for a MBIM IP session with SessionId 1:
85
86  ip link add dev wwan0-1 parentdev wwan0 type wwan linkid 1
87
88The driver will automatically map the "wwan0-1" network device to MBIM IP
89session 1.
90
91AT port userspace ABI
92----------------------------------
93
94/dev/wwan0at0 character device
95~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
96The driver exposes an AT port by implementing AT WWAN Port.
97The userspace end of the control port is a /dev/wwan0at0 character
98device. Application shall use this interface to issue AT commands.
99
100The MediaTek's T700 modem supports the 3GPP TS 27.007 [4] specification.
101
102References
103==========
104[1] *MBIM (Mobile Broadband Interface Model) Errata-1*
105
106- https://www.usb.org/document-library/
107
108[2] *libmbim "a glib-based library for talking to WWAN modems and devices which
109speak the Mobile Interface Broadband Model (MBIM) protocol"*
110
111- http://www.freedesktop.org/wiki/Software/libmbim/
112
113[3] *Modem Manager "a DBus-activated daemon which controls mobile broadband
114(2G/3G/4G/5G) devices and connections"*
115
116- http://www.freedesktop.org/wiki/Software/ModemManager/
117
118[4] *Specification # 27.007 - 3GPP*
119
120- https://www.3gpp.org/DynaReport/27007.htm
121