198 lines
6.5 KiB
ReStructuredText
198 lines
6.5 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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============
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Rmnet Driver
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============
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1. Introduction
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===============
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rmnet driver is used for supporting the Multiplexing and aggregation
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Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm
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Technologies, Inc. modems.
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This driver can be used to register onto any physical network device in
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IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.
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Multiplexing allows for creation of logical netdevices (rmnet devices) to
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handle multiple private data networks (PDN) like a default internet, tethering,
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multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends
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packets with MAP headers to rmnet. Based on the multiplexer id, rmnet
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routes to the appropriate PDN after removing the MAP header.
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Aggregation is required to achieve high data rates. This involves hardware
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sending aggregated bunch of MAP frames. rmnet driver will de-aggregate
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these MAP frames and send them to appropriate PDN's.
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2. Packet format
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================
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a. MAP packet v1 (data / control)
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MAP header fields are in big endian format.
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Packet format::
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Bit 0 1 2-7 8-15 16-31
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Function Command / Data Reserved Pad Multiplexer ID Payload length
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Bit 32-x
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Function Raw bytes
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Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
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or data packet. Command packet is used for transport level flow control. Data
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packets are standard IP packets.
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Reserved bits must be zero when sent and ignored when received.
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Padding is the number of bytes to be appended to the payload to
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ensure 4 byte alignment.
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Multiplexer ID is to indicate the PDN on which data has to be sent.
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Payload length includes the padding length but does not include MAP header
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length.
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b. Map packet v4 (data / control)
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MAP header fields are in big endian format.
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Packet format::
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Bit 0 1 2-7 8-15 16-31
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Function Command / Data Reserved Pad Multiplexer ID Payload length
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Bit 32-(x-33) (x-32)-x
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Function Raw bytes Checksum offload header
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Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
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or data packet. Command packet is used for transport level flow control. Data
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packets are standard IP packets.
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Reserved bits must be zero when sent and ignored when received.
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Padding is the number of bytes to be appended to the payload to
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ensure 4 byte alignment.
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Multiplexer ID is to indicate the PDN on which data has to be sent.
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Payload length includes the padding length but does not include MAP header
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length.
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Checksum offload header, has the information about the checksum processing done
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by the hardware.Checksum offload header fields are in big endian format.
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Packet format::
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Bit 0-14 15 16-31
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Function Reserved Valid Checksum start offset
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Bit 31-47 48-64
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Function Checksum length Checksum value
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Reserved bits must be zero when sent and ignored when received.
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Valid bit indicates whether the partial checksum is calculated and is valid.
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Set to 1, if its is valid. Set to 0 otherwise.
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Padding is the number of bytes to be appended to the payload to
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ensure 4 byte alignment.
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Checksum start offset, Indicates the offset in bytes from the beginning of the
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IP header, from which modem computed checksum.
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Checksum length is the Length in bytes starting from CKSUM_START_OFFSET,
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over which checksum is computed.
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Checksum value, indicates the checksum computed.
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c. MAP packet v5 (data / control)
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MAP header fields are in big endian format.
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Packet format::
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Bit 0 1 2-7 8-15 16-31
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Function Command / Data Next header Pad Multiplexer ID Payload length
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Bit 32-x
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Function Raw bytes
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Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
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or data packet. Command packet is used for transport level flow control. Data
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packets are standard IP packets.
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Next header is used to indicate the presence of another header, currently is
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limited to checksum header.
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Padding is the number of bytes to be appended to the payload to
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ensure 4 byte alignment.
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Multiplexer ID is to indicate the PDN on which data has to be sent.
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Payload length includes the padding length but does not include MAP header
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length.
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d. Checksum offload header v5
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Checksum offload header fields are in big endian format.
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Bit 0 - 6 7 8-15 16-31
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Function Header Type Next Header Checksum Valid Reserved
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Header Type is to indicate the type of header, this usually is set to CHECKSUM
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Header types
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= ==========================================
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0 Reserved
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1 Reserved
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2 checksum header
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Checksum Valid is to indicate whether the header checksum is valid. Value of 1
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implies that checksum is calculated on this packet and is valid, value of 0
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indicates that the calculated packet checksum is invalid.
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Reserved bits must be zero when sent and ignored when received.
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e. MAP packet v1/v5 (command specific)::
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Bit 0 1 2-7 8 - 15 16 - 31
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Function Command Reserved Pad Multiplexer ID Payload length
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Bit 32 - 39 40 - 45 46 - 47 48 - 63
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Function Command name Reserved Command Type Reserved
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Bit 64 - 95
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Function Transaction ID
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Bit 96 - 127
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Function Command data
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Command 1 indicates disabling flow while 2 is enabling flow
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Command types
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= ==========================================
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0 for MAP command request
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1 is to acknowledge the receipt of a command
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2 is for unsupported commands
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3 is for error during processing of commands
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= ==========================================
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f. Aggregation
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Aggregation is multiple MAP packets (can be data or command) delivered to
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rmnet in a single linear skb. rmnet will process the individual
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packets and either ACK the MAP command or deliver the IP packet to the
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network stack as needed
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MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....
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MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...
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3. Userspace configuration
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==========================
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rmnet userspace configuration is done through netlink library librmnetctl
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and command line utility rmnetcli. Utility is hosted in codeaurora forum git.
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The driver uses rtnl_link_ops for communication.
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https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl
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