| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ============ |
| Rmnet Driver |
| ============ |
| |
| 1. Introduction |
| =============== |
| |
| rmnet driver is used for supporting the Multiplexing and aggregation |
| Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm |
| Technologies, Inc. modems. |
| |
| This driver can be used to register onto any physical network device in |
| IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. |
| |
| Multiplexing allows for creation of logical netdevices (rmnet devices) to |
| handle multiple private data networks (PDN) like a default internet, tethering, |
| multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends |
| packets with MAP headers to rmnet. Based on the multiplexer id, rmnet |
| routes to the appropriate PDN after removing the MAP header. |
| |
| Aggregation is required to achieve high data rates. This involves hardware |
| sending aggregated bunch of MAP frames. rmnet driver will de-aggregate |
| these MAP frames and send them to appropriate PDN's. |
| |
| 2. Packet format |
| ================ |
| |
| a. MAP packet v1 (data / control) |
| |
| MAP header fields are in big endian format. |
| |
| Packet format:: |
| |
| Bit 0 1 2-7 8-15 16-31 |
| Function Command / Data Reserved Pad Multiplexer ID Payload length |
| |
| Bit 32-x |
| Function Raw bytes |
| |
| Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command |
| or data packet. Command packet is used for transport level flow control. Data |
| packets are standard IP packets. |
| |
| Reserved bits must be zero when sent and ignored when received. |
| |
| Padding is the number of bytes to be appended to the payload to |
| ensure 4 byte alignment. |
| |
| Multiplexer ID is to indicate the PDN on which data has to be sent. |
| |
| Payload length includes the padding length but does not include MAP header |
| length. |
| |
| b. Map packet v4 (data / control) |
| |
| MAP header fields are in big endian format. |
| |
| Packet format:: |
| |
| Bit 0 1 2-7 8-15 16-31 |
| Function Command / Data Reserved Pad Multiplexer ID Payload length |
| |
| Bit 32-(x-33) (x-32)-x |
| Function Raw bytes Checksum offload header |
| |
| Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command |
| or data packet. Command packet is used for transport level flow control. Data |
| packets are standard IP packets. |
| |
| Reserved bits must be zero when sent and ignored when received. |
| |
| Padding is the number of bytes to be appended to the payload to |
| ensure 4 byte alignment. |
| |
| Multiplexer ID is to indicate the PDN on which data has to be sent. |
| |
| Payload length includes the padding length but does not include MAP header |
| length. |
| |
| Checksum offload header, has the information about the checksum processing done |
| by the hardware.Checksum offload header fields are in big endian format. |
| |
| Packet format:: |
| |
| Bit 0-14 15 16-31 |
| Function Reserved Valid Checksum start offset |
| |
| Bit 31-47 48-64 |
| Function Checksum length Checksum value |
| |
| Reserved bits must be zero when sent and ignored when received. |
| |
| Valid bit indicates whether the partial checksum is calculated and is valid. |
| Set to 1, if its is valid. Set to 0 otherwise. |
| |
| Padding is the number of bytes to be appended to the payload to |
| ensure 4 byte alignment. |
| |
| Checksum start offset, Indicates the offset in bytes from the beginning of the |
| IP header, from which modem computed checksum. |
| |
| Checksum length is the Length in bytes starting from CKSUM_START_OFFSET, |
| over which checksum is computed. |
| |
| Checksum value, indicates the checksum computed. |
| |
| c. MAP packet v5 (data / control) |
| |
| MAP header fields are in big endian format. |
| |
| Packet format:: |
| |
| Bit 0 1 2-7 8-15 16-31 |
| Function Command / Data Next header Pad Multiplexer ID Payload length |
| |
| Bit 32-x |
| Function Raw bytes |
| |
| Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command |
| or data packet. Command packet is used for transport level flow control. Data |
| packets are standard IP packets. |
| |
| Next header is used to indicate the presence of another header, currently is |
| limited to checksum header. |
| |
| Padding is the number of bytes to be appended to the payload to |
| ensure 4 byte alignment. |
| |
| Multiplexer ID is to indicate the PDN on which data has to be sent. |
| |
| Payload length includes the padding length but does not include MAP header |
| length. |
| |
| d. Checksum offload header v5 |
| |
| Checksum offload header fields are in big endian format. |
| |
| Bit 0 - 6 7 8-15 16-31 |
| Function Header Type Next Header Checksum Valid Reserved |
| |
| Header Type is to indicate the type of header, this usually is set to CHECKSUM |
| |
| Header types |
| = ========================================== |
| 0 Reserved |
| 1 Reserved |
| 2 checksum header |
| |
| Checksum Valid is to indicate whether the header checksum is valid. Value of 1 |
| implies that checksum is calculated on this packet and is valid, value of 0 |
| indicates that the calculated packet checksum is invalid. |
| |
| Reserved bits must be zero when sent and ignored when received. |
| |
| e. MAP packet v1/v5 (command specific):: |
| |
| Bit 0 1 2-7 8 - 15 16 - 31 |
| Function Command Reserved Pad Multiplexer ID Payload length |
| Bit 32 - 39 40 - 45 46 - 47 48 - 63 |
| Function Command name Reserved Command Type Reserved |
| Bit 64 - 95 |
| Function Transaction ID |
| Bit 96 - 127 |
| Function Command data |
| |
| Command 1 indicates disabling flow while 2 is enabling flow |
| |
| Command types |
| |
| = ========================================== |
| 0 for MAP command request |
| 1 is to acknowledge the receipt of a command |
| 2 is for unsupported commands |
| 3 is for error during processing of commands |
| = ========================================== |
| |
| f. Aggregation |
| |
| Aggregation is multiple MAP packets (can be data or command) delivered to |
| rmnet in a single linear skb. rmnet will process the individual |
| packets and either ACK the MAP command or deliver the IP packet to the |
| network stack as needed |
| |
| MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... |
| |
| MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... |
| |
| 3. Userspace configuration |
| ========================== |
| |
| rmnet userspace configuration is done through netlink using iproute2 |
| https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/ |
| |
| The driver uses rtnl_link_ops for communication. |
