Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst

Source file repositories/reference/linux-study-clean/Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst

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Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst
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.. SPDX-License-Identifier: GPL-2.0

============
Rmnet Driver
============

1. Introduction
===============

rmnet driver is used for supporting the Multiplexing and aggregation
Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm
Technologies, Inc. modems.

This driver can be used to register onto any physical network device in
IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.

Multiplexing allows for creation of logical netdevices (rmnet devices) to
handle multiple private data networks (PDN) like a default internet, tethering,
multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends
packets with MAP headers to rmnet. Based on the multiplexer id, rmnet
routes to the appropriate PDN after removing the MAP header.

Aggregation is required to achieve high data rates. This involves hardware
sending aggregated bunch of MAP frames. rmnet driver will de-aggregate
these MAP frames and send them to appropriate PDN's.

2. Packet format
================

a. MAP packet v1 (data / control)
---------------------------------

MAP header fields are in big endian format.

Packet format::

  Bit             0             1           2-7      8-15           16-31
  Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length

  Bit            32-x
  Function      Raw bytes

Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
or data packet. Command packet is used for transport level flow control. Data
packets are standard IP packets.

Reserved bits must be zero when sent and ignored when received.

Padding is the number of bytes to be appended to the payload to
ensure 4 byte alignment.

Multiplexer ID is to indicate the PDN on which data has to be sent.

Payload length includes the padding length but does not include MAP header
length.

b. Map packet v4 (data / control)
---------------------------------

MAP header fields are in big endian format.

Packet format::

  Bit             0             1           2-7      8-15           16-31
  Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length

  Bit            32-(x-33)      (x-32)-x
  Function      Raw bytes      Checksum offload header

Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command

Annotation

Implementation Notes