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1.. SPDX-License-Identifier: GPL-2.02 3============4Rmnet Driver5============6 71. Introduction8===============9 10rmnet driver is used for supporting the Multiplexing and aggregation11Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm12Technologies, Inc. modems.13 14This driver can be used to register onto any physical network device in15IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.16 17Multiplexing allows for creation of logical netdevices (rmnet devices) to18handle multiple private data networks (PDN) like a default internet, tethering,19multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends20packets with MAP headers to rmnet. Based on the multiplexer id, rmnet21routes to the appropriate PDN after removing the MAP header.22 23Aggregation is required to achieve high data rates. This involves hardware24sending aggregated bunch of MAP frames. rmnet driver will de-aggregate25these MAP frames and send them to appropriate PDN's.26 272. Packet format28================29 30a. MAP packet v1 (data / control)31 32MAP header fields are in big endian format.33 34Packet format::35 36 Bit 0 1 2-7 8-15 16-3137 Function Command / Data Reserved Pad Multiplexer ID Payload length38 39 Bit 32-x40 Function Raw bytes41 42Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command43or data packet. Command packet is used for transport level flow control. Data44packets are standard IP packets.45 46Reserved bits must be zero when sent and ignored when received.47 48Padding is the number of bytes to be appended to the payload to49ensure 4 byte alignment.50 51Multiplexer ID is to indicate the PDN on which data has to be sent.52 53Payload length includes the padding length but does not include MAP header54length.55 56b. Map packet v4 (data / control)57 58MAP header fields are in big endian format.59 60Packet format::61 62 Bit 0 1 2-7 8-15 16-3163 Function Command / Data Reserved Pad Multiplexer ID Payload length64 65 Bit 32-(x-33) (x-32)-x66 Function Raw bytes Checksum offload header67 68Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command69or data packet. Command packet is used for transport level flow control. Data70packets are standard IP packets.71 72Reserved bits must be zero when sent and ignored when received.73 74Padding is the number of bytes to be appended to the payload to75ensure 4 byte alignment.76 77Multiplexer ID is to indicate the PDN on which data has to be sent.78 79Payload length includes the padding length but does not include MAP header80length.81 82Checksum offload header, has the information about the checksum processing done83by the hardware.Checksum offload header fields are in big endian format.84 85Packet format::86 87 Bit 0-14 15 16-3188 Function Reserved Valid Checksum start offset89 90 Bit 31-47 48-6491 Function Checksum length Checksum value92 93Reserved bits must be zero when sent and ignored when received.94 95Valid bit indicates whether the partial checksum is calculated and is valid.96Set to 1, if its is valid. Set to 0 otherwise.97 98Padding is the number of bytes to be appended to the payload to99ensure 4 byte alignment.100 101Checksum start offset, Indicates the offset in bytes from the beginning of the102IP header, from which modem computed checksum.103 104Checksum length is the Length in bytes starting from CKSUM_START_OFFSET,105over which checksum is computed.106 107Checksum value, indicates the checksum computed.108 109c. MAP packet v5 (data / control)110 111MAP header fields are in big endian format.112 113Packet format::114 115 Bit 0 1 2-7 8-15 16-31116 Function Command / Data Next header Pad Multiplexer ID Payload length117 118 Bit 32-x119 Function Raw bytes120 121Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command122or data packet. Command packet is used for transport level flow control. Data123packets are standard IP packets.124 125Next header is used to indicate the presence of another header, currently is126limited to checksum header.127 128Padding is the number of bytes to be appended to the payload to129ensure 4 byte alignment.130 131Multiplexer ID is to indicate the PDN on which data has to be sent.132 133Payload length includes the padding length but does not include MAP header134length.135 136d. Checksum offload header v5137 138Checksum offload header fields are in big endian format.139 140 Bit 0 - 6 7 8-15 16-31141 Function Header Type Next Header Checksum Valid Reserved142 143Header Type is to indicate the type of header, this usually is set to CHECKSUM144 145Header types146= ==========================================1470 Reserved1481 Reserved1492 checksum header150 151Checksum Valid is to indicate whether the header checksum is valid. Value of 1152implies that checksum is calculated on this packet and is valid, value of 0153indicates that the calculated packet checksum is invalid.154 155Reserved bits must be zero when sent and ignored when received.156 157e. MAP packet v1/v5 (command specific)::158 159 Bit 0 1 2-7 8 - 15 16 - 31160 Function Command Reserved Pad Multiplexer ID Payload length161 Bit 32 - 39 40 - 45 46 - 47 48 - 63162 Function Command name Reserved Command Type Reserved163 Bit 64 - 95164 Function Transaction ID165 Bit 96 - 127166 Function Command data167 168Command 1 indicates disabling flow while 2 is enabling flow169 170Command types171 172= ==========================================1730 for MAP command request1741 is to acknowledge the receipt of a command1752 is for unsupported commands1763 is for error during processing of commands177= ==========================================178 179f. Aggregation180 181Aggregation is multiple MAP packets (can be data or command) delivered to182rmnet in a single linear skb. rmnet will process the individual183packets and either ACK the MAP command or deliver the IP packet to the184network stack as needed185 186MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....187 188MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...189 1903. Userspace configuration191==========================192 193rmnet userspace configuration is done through netlink using iproute2194https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/195 196The driver uses rtnl_link_ops for communication.197