1.. SPDX-License-Identifier: GPL-2.0 2 3============ 4Rmnet Driver 5============ 6 71. Introduction 8=============== 9 10rmnet driver is used for supporting the Multiplexing and aggregation 11Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm 12Technologies, Inc. modems. 13 14This driver can be used to register onto any physical network device in 15IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. 16 17Multiplexing allows for creation of logical netdevices (rmnet devices) to 18handle multiple private data networks (PDN) like a default internet, tethering, 19multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends 20packets with MAP headers to rmnet. Based on the multiplexer id, rmnet 21routes to the appropriate PDN after removing the MAP header. 22 23Aggregation is required to achieve high data rates. This involves hardware 24sending aggregated bunch of MAP frames. rmnet driver will de-aggregate 25these MAP frames and send them to appropriate PDN's. 26 272. Packet format 28================ 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 16-31 37 Function Command / Data Reserved Pad Multiplexer ID Payload length 38 39 Bit 32-x 40 Function Raw bytes 41 42Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 43or data packet. Command packet is used for transport level flow control. Data 44packets 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 to 49ensure 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 header 54length. 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 16-31 63 Function Command / Data Reserved Pad Multiplexer ID Payload length 64 65 Bit 32-(x-33) (x-32)-x 66 Function Raw bytes Checksum offload header 67 68Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 69or data packet. Command packet is used for transport level flow control. Data 70packets 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 to 75ensure 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 header 80length. 81 82Checksum offload header, has the information about the checksum processing done 83by the hardware.Checksum offload header fields are in big endian format. 84 85Packet format:: 86 87 Bit 0-14 15 16-31 88 Function Reserved Valid Checksum start offset 89 90 Bit 31-47 48-64 91 Function Checksum length Checksum value 92 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 to 99ensure 4 byte alignment. 100 101Checksum start offset, Indicates the offset in bytes from the beginning of the 102IP 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 16-31 116 Function Command / Data Next header Pad Multiplexer ID Payload length 117 118 Bit 32-x 119 Function Raw bytes 120 121Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 122or data packet. Command packet is used for transport level flow control. Data 123packets are standard IP packets. 124 125Next header is used to indicate the presence of another header, currently is 126limited to checksum header. 127 128Padding is the number of bytes to be appended to the payload to 129ensure 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 header 134length. 135 136d. Checksum offload header v5 137 138Checksum offload header fields are in big endian format. 139 140Packet format:: 141 142 Bit 0 - 6 7 8-15 16-31 143 Function Header Type Next Header Checksum Valid Reserved 144 145Header Type is to indicate the type of header, this usually is set to CHECKSUM 146 147Header types 148 149= =============== 1500 Reserved 1511 Reserved 1522 checksum header 153= =============== 154 155Checksum Valid is to indicate whether the header checksum is valid. Value of 1 156implies that checksum is calculated on this packet and is valid, value of 0 157indicates that the calculated packet checksum is invalid. 158 159Reserved bits must be zero when sent and ignored when received. 160 161e. MAP packet v1/v5 (command specific):: 162 163 Bit 0 1 2-7 8 - 15 16 - 31 164 Function Command Reserved Pad Multiplexer ID Payload length 165 Bit 32 - 39 40 - 45 46 - 47 48 - 63 166 Function Command name Reserved Command Type Reserved 167 Bit 64 - 95 168 Function Transaction ID 169 Bit 96 - 127 170 Function Command data 171 172Command 1 indicates disabling flow while 2 is enabling flow 173 174Command types 175 176= ========================================== 1770 for MAP command request 1781 is to acknowledge the receipt of a command 1792 is for unsupported commands 1803 is for error during processing of commands 181= ========================================== 182 183f. Aggregation 184 185Aggregation is multiple MAP packets (can be data or command) delivered to 186rmnet in a single linear skb. rmnet will process the individual 187packets and either ACK the MAP command or deliver the IP packet to the 188network stack as needed 189 190Packet format:: 191 192 MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... 193 194 MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... 195 1963. Userspace configuration 197========================== 198 199rmnet userspace configuration is done through netlink using iproute2 200https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/ 201 202The driver uses rtnl_link_ops for communication. 203