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ceed73a2 SAK |
1 | 1. Introduction |
2 | ||
3 | rmnet driver is used for supporting the Multiplexing and aggregation | |
4 | Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm | |
5 | Technologies, Inc. modems. | |
6 | ||
7 | This driver can be used to register onto any physical network device in | |
8 | IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. | |
9 | ||
10 | Multiplexing allows for creation of logical netdevices (rmnet devices) to | |
11 | handle multiple private data networks (PDN) like a default internet, tethering, | |
12 | multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends | |
13 | packets with MAP headers to rmnet. Based on the multiplexer id, rmnet | |
14 | routes to the appropriate PDN after removing the MAP header. | |
15 | ||
16 | Aggregation is required to achieve high data rates. This involves hardware | |
17 | sending aggregated bunch of MAP frames. rmnet driver will de-aggregate | |
18 | these MAP frames and send them to appropriate PDN's. | |
19 | ||
20 | 2. Packet format | |
21 | ||
22 | a. MAP packet (data / control) | |
23 | ||
24 | MAP header has the same endianness of the IP packet. | |
25 | ||
26 | Packet format - | |
27 | ||
28 | Bit 0 1 2-7 8 - 15 16 - 31 | |
29 | Function Command / Data Reserved Pad Multiplexer ID Payload length | |
30 | Bit 32 - x | |
31 | Function Raw Bytes | |
32 | ||
33 | Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command | |
34 | or data packet. Control packet is used for transport level flow control. Data | |
35 | packets are standard IP packets. | |
36 | ||
37 | Reserved bits are usually zeroed out and to be ignored by receiver. | |
38 | ||
39 | Padding is number of bytes to be added for 4 byte alignment if required by | |
40 | hardware. | |
41 | ||
42 | Multiplexer ID is to indicate the PDN on which data has to be sent. | |
43 | ||
44 | Payload length includes the padding length but does not include MAP header | |
45 | length. | |
46 | ||
47 | b. MAP packet (command specific) | |
48 | ||
49 | Bit 0 1 2-7 8 - 15 16 - 31 | |
50 | Function Command Reserved Pad Multiplexer ID Payload length | |
51 | Bit 32 - 39 40 - 45 46 - 47 48 - 63 | |
52 | Function Command name Reserved Command Type Reserved | |
53 | Bit 64 - 95 | |
54 | Function Transaction ID | |
55 | Bit 96 - 127 | |
56 | Function Command data | |
57 | ||
58 | Command 1 indicates disabling flow while 2 is enabling flow | |
59 | ||
60 | Command types - | |
61 | 0 for MAP command request | |
62 | 1 is to acknowledge the receipt of a command | |
63 | 2 is for unsupported commands | |
64 | 3 is for error during processing of commands | |
65 | ||
66 | c. Aggregation | |
67 | ||
68 | Aggregation is multiple MAP packets (can be data or command) delivered to | |
69 | rmnet in a single linear skb. rmnet will process the individual | |
70 | packets and either ACK the MAP command or deliver the IP packet to the | |
71 | network stack as needed | |
72 | ||
73 | MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... | |
74 | MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... | |
75 | ||
76 | 3. Userspace configuration | |
77 | ||
78 | rmnet userspace configuration is done through netlink library librmnetctl | |
79 | and command line utility rmnetcli. Utility is hosted in codeaurora forum git. | |
80 | The driver uses rtnl_link_ops for communication. | |
81 | ||
82 | https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl |