| 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 (data / control) |
| |
| MAP header has the same endianness of the IP packet. |
| |
| 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. Control packet is used for transport level flow control. Data |
| packets are standard IP packets. |
| |
| Reserved bits are usually zeroed out and to be ignored by receiver. |
| |
| Padding is number of bytes to be added for 4 byte alignment if required by |
| hardware. |
| |
| 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 (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 |
| |
| c. 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 library librmnetctl |
| and command line utility rmnetcli. Utility is hosted in codeaurora forum git. |
| The driver uses rtnl_link_ops for communication. |
| |
| https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl |