121 lines
4.2 KiB
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121 lines
4.2 KiB
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.. SPDX-License-Identifier: GPL-2.0-only
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.. Copyright (C) 2020-21 Intel Corporation
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.. _t7xx_driver_doc:
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============================================
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t7xx driver for MTK PCIe based T700 5G modem
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============================================
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The t7xx driver is a WWAN PCIe host driver developed for linux or Chrome OS platforms
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for data exchange over PCIe interface between Host platform & MediaTek's T700 5G modem.
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The driver exposes an interface conforming to the MBIM protocol [1]. Any front end
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application (e.g. Modem Manager) could easily manage the MBIM interface to enable
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data communication towards WWAN. The driver also provides an interface to interact
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with the MediaTek's modem via AT commands.
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Basic usage
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===========
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MBIM & AT functions are inactive when unmanaged. The t7xx driver provides
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WWAN port userspace interfaces representing MBIM & AT control channels and does
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not play any role in managing their functionality. It is the job of a userspace
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application to detect port enumeration and enable MBIM & AT functionalities.
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Examples of few such userspace applications are:
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- mbimcli (included with the libmbim [2] library), and
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- Modem Manager [3]
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Management Applications to carry out below required actions for establishing
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MBIM IP session:
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- open the MBIM control channel
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- configure network connection settings
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- connect to network
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- configure IP network interface
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Management Applications to carry out below required actions for send an AT
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command and receive response:
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- open the AT control channel using a UART tool or a special user tool
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Management application development
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==================================
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The driver and userspace interfaces are described below. The MBIM protocol is
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described in [1] Mobile Broadband Interface Model v1.0 Errata-1.
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MBIM control channel userspace ABI
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----------------------------------
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/dev/wwan0mbim0 character device
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The driver exposes an MBIM interface to the MBIM function by implementing
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MBIM WWAN Port. The userspace end of the control channel pipe is a
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/dev/wwan0mbim0 character device. Application shall use this interface for
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MBIM protocol communication.
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Fragmentation
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~~~~~~~~~~~~~
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The userspace application is responsible for all control message fragmentation
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and defragmentation as per MBIM specification.
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/dev/wwan0mbim0 write()
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~~~~~~~~~~~~~~~~~~~~~~~
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The MBIM control messages from the management application must not exceed the
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negotiated control message size.
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/dev/wwan0mbim0 read()
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~~~~~~~~~~~~~~~~~~~~~~
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The management application must accept control messages of up the negotiated
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control message size.
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MBIM data channel userspace ABI
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-------------------------------
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wwan0-X network device
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~~~~~~~~~~~~~~~~~~~~~~
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The t7xx driver exposes IP link interface "wwan0-X" of type "wwan" for IP
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traffic. Iproute network utility is used for creating "wwan0-X" network
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interface and for associating it with MBIM IP session.
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The userspace management application is responsible for creating new IP link
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prior to establishing MBIM IP session where the SessionId is greater than 0.
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For example, creating new IP link for a MBIM IP session with SessionId 1:
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ip link add dev wwan0-1 parentdev wwan0 type wwan linkid 1
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The driver will automatically map the "wwan0-1" network device to MBIM IP
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session 1.
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AT port userspace ABI
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----------------------------------
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/dev/wwan0at0 character device
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The driver exposes an AT port by implementing AT WWAN Port.
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The userspace end of the control port is a /dev/wwan0at0 character
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device. Application shall use this interface to issue AT commands.
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The MediaTek's T700 modem supports the 3GPP TS 27.007 [4] specification.
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References
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==========
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[1] *MBIM (Mobile Broadband Interface Model) Errata-1*
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- https://www.usb.org/document-library/
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[2] *libmbim "a glib-based library for talking to WWAN modems and devices which
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speak the Mobile Interface Broadband Model (MBIM) protocol"*
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- http://www.freedesktop.org/wiki/Software/libmbim/
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[3] *Modem Manager "a DBus-activated daemon which controls mobile broadband
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(2G/3G/4G/5G) devices and connections"*
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- http://www.freedesktop.org/wiki/Software/ModemManager/
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[4] *Specification # 27.007 - 3GPP*
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- https://www.3gpp.org/DynaReport/27007.htm
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