drivers: net: rmnet: Initial implementation

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

https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/\

dataservices/tree/rmnetctl

source "drivers/net/hyperv/Kconfig"

source "drivers/net/rmnet/Kconfig"

endif # NETDEVICES

obj-$(CONFIG_NTB_NETDEV) += ntb_netdev.o

obj-$(CONFIG_FUJITSU_ES) += fjes/

obj-$(CONFIG_RMNET) += rmnet/

#

# RMNET MAP driver

#

menuconfig RMNET

	depends on NETDEVICES

	bool "RmNet MAP driver"

	---help---

	  If you say Y here, then the rmnet module will be statically

	  compiled into the kernel. The rmnet module provides MAP

	  functionality for embedded and bridged traffic.

if RMNET

config RMNET_DEBUG

	bool "RmNet Debug Logging"

	---help---

	  Say Y here if you want RmNet to be able to log packets in main

	  system log. This should not be enabled on production builds as it can

	  impact system performance. Note that simply enabling it here will not

	  enable the logging; it must be enabled at run-time as well.

endif # RMNET

#

# Makefile for the RMNET module

#

rmnet-y		 := rmnet_main.o

rmnet-y		 += rmnet_config.o

rmnet-y		 += rmnet_vnd.o

rmnet-y		 += rmnet_handlers.o

rmnet-y		 += rmnet_map_data.o

rmnet-y		 += rmnet_map_command.o

rmnet-y		 += rmnet_stats.o

obj-$(CONFIG_RMNET) += rmnet.o

CFLAGS_rmnet_main.o := -I$(src)