1 .. SPDX-License-Identifier: GPL-2.0 2 3 ============ 4 Rmnet Driver 5 ============ 6 7 1. Introduction 8 =============== 9 10 rmnet driver is used for supporting the Multiplexing and aggregation 11 Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm 12 Technologies, Inc. modems. 13 14 This driver can be used to register onto any physical network device in 15 IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. 16 17 Multiplexing allows for creation of logical netdevices (rmnet devices) to 18 handle multiple private data networks (PDN) like a default internet, tethering, 19 multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends 20 packets with MAP headers to rmnet. Based on the multiplexer id, rmnet 21 routes to the appropriate PDN after removing the MAP header. 22 23 Aggregation is required to achieve high data rates. This involves hardware 24 sending aggregated bunch of MAP frames. rmnet driver will de-aggregate 25 these MAP frames and send them to appropriate PDN's. 26 27 2. Packet format 28 ================ 29 30 a. MAP packet v1 (data / control) 31 32 MAP header fields are in big endian format. 33 34 Packet 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 42 Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 43 or data packet. Command packet is used for transport level flow control. Data 44 packets are standard IP packets. 45 46 Reserved bits must be zero when sent and ignored when received. 47 48 Padding is the number of bytes to be appended to the payload to 49 ensure 4 byte alignment. 50 51 Multiplexer ID is to indicate the PDN on which data has to be sent. 52 53 Payload length includes the padding length but does not include MAP header 54 length. 55 56 b. Map packet v4 (data / control) 57 58 MAP header fields are in big endian format. 59 60 Packet 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 68 Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 69 or data packet. Command packet is used for transport level flow control. Data 70 packets are standard IP packets. 71 72 Reserved bits must be zero when sent and ignored when received. 73 74 Padding is the number of bytes to be appended to the payload to 75 ensure 4 byte alignment. 76 77 Multiplexer ID is to indicate the PDN on which data has to be sent. 78 79 Payload length includes the padding length but does not include MAP header 80 length. 81 82 Checksum offload header, has the information about the checksum processing done 83 by the hardware.Checksum offload header fields are in big endian format. 84 85 Packet 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 93 Reserved bits must be zero when sent and ignored when received. 94 95 Valid bit indicates whether the partial checksum is calculated and is valid. 96 Set to 1, if its is valid. Set to 0 otherwise. 97 98 Padding is the number of bytes to be appended to the payload to 99 ensure 4 byte alignment. 100 101 Checksum start offset, Indicates the offset in bytes from the beginning of the 102 IP header, from which modem computed checksum. 103 104 Checksum length is the Length in bytes starting from CKSUM_START_OFFSET, 105 over which checksum is computed. 106 107 Checksum value, indicates the checksum computed. 108 109 c. MAP packet v5 (data / control) 110 111 MAP header fields are in big endian format. 112 113 Packet 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 120 121 Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command 122 or data packet. Command packet is used for transport level flow control. Data 123 packets are standard IP packets. 124 125 Next header is used to indicate the presence of another header, currently is 126 limited to checksum header. 127 128 Padding is the number of bytes to be appended to the payload to 129 ensure 4 byte alignment. 130 131 Multiplexer ID is to indicate the PDN on which data has to be sent. 132 133 Payload length includes the padding length but does not include MAP header 134 length. 135 136 d. Checksum offload header v5 137 138 Checksum offload header fields are in big endian format. 139 140 Bit 0 - 6 7 8-15 16-31 141 Function Header Type Next Header Checksum Valid Reserved 142 143 Header Type is to indicate the type of header, this usually is set to CHECKSUM 144 145 Header types 146 = ========================================== 147 0 Reserved 148 1 Reserved 149 2 checksum header 150 151 Checksum Valid is to indicate whether the header checksum is valid. Value of 1 152 implies that checksum is calculated on this packet and is valid, value of 0 153 indicates that the calculated packet checksum is invalid. 154 155 Reserved bits must be zero when sent and ignored when received. 156 157 e. MAP packet v1/v5 (command specific):: 158 159 Bit 0 1 2-7 8 - 15 16 - 31 160 Function Command Reserved Pad Multiplexer ID Payload length 161 Bit 32 - 39 40 - 45 46 - 47 48 - 63 162 Function Command name Reserved Command Type Reserved 163 Bit 64 - 95 164 Function Transaction ID 165 Bit 96 - 127 166 Function Command data 167 168 Command 1 indicates disabling flow while 2 is enabling flow 169 170 Command types 171 172 = ========================================== 173 0 for MAP command request 174 1 is to acknowledge the receipt of a command 175 2 is for unsupported commands 176 3 is for error during processing of commands 177 = ========================================== 178 179 f. Aggregation 180 181 Aggregation is multiple MAP packets (can be data or command) delivered to 182 rmnet in a single linear skb. rmnet will process the individual 183 packets and either ACK the MAP command or deliver the IP packet to the 184 network stack as needed 185 186 MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... 187 188 MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... 189 190 3. Userspace configuration 191 ========================== 192 193 rmnet userspace configuration is done through netlink using iproute2 194 https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/ 195 196 The driver uses rtnl_link_ops for communication.
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