83 lines
3 KiB
Plaintext
83 lines
3 KiB
Plaintext
1. Introduction
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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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a. MAP packet (data / control)
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MAP header has the same endianness of the IP packet.
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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. Control packet is used for transport level flow control. Data
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packets are standard IP packets.
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Reserved bits are usually zeroed out and to be ignored by receiver.
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Padding is number of bytes to be added for 4 byte alignment if required by
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hardware.
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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 (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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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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c. 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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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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