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 (data / control)
31
32MAP header has the same endianness of the IP packet.
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  Bit            32 - x
39  Function     Raw  Bytes
40
41Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
42or data packet. Control packet is used for transport level flow control. Data
43packets are standard IP packets.
44
45Reserved bits are usually zeroed out and to be ignored by receiver.
46
47Padding is number of bytes to be added for 4 byte alignment if required by
48hardware.
49
50Multiplexer ID is to indicate the PDN on which data has to be sent.
51
52Payload length includes the padding length but does not include MAP header
53length.
54
55b. MAP packet (command specific)::
56
57    Bit             0             1           2-7      8 - 15           16 - 31
58    Function   Command         Reserved     Pad   Multiplexer ID    Payload length
59    Bit          32 - 39        40 - 45    46 - 47       48 - 63
60    Function   Command name    Reserved   Command Type   Reserved
61    Bit          64 - 95
62    Function   Transaction ID
63    Bit          96 - 127
64    Function   Command data
65
66Command 1 indicates disabling flow while 2 is enabling flow
67
68Command types
69
70= ==========================================
710 for MAP command request
721 is to acknowledge the receipt of a command
732 is for unsupported commands
743 is for error during processing of commands
75= ==========================================
76
77c. Aggregation
78
79Aggregation is multiple MAP packets (can be data or command) delivered to
80rmnet in a single linear skb. rmnet will process the individual
81packets and either ACK the MAP command or deliver the IP packet to the
82network stack as needed
83
84MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....
85
86MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...
87
883. Userspace configuration
89==========================
90
91rmnet userspace configuration is done through netlink library librmnetctl
92and command line utility rmnetcli. Utility is hosted in codeaurora forum git.
93The driver uses rtnl_link_ops for communication.
94
95https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl
96