Commit 710b797c authored by Sharath Chandra Vurukala's avatar Sharath Chandra Vurukala Committed by David S. Miller
Browse files

docs: networking: Add documentation for MAPv5 



Adding documentation explaining the new MAPv4/v5 packet formats
and the corresponding checksum offload headers.

Signed-off-by: default avatarSharath Chandra Vurukala <sharathv@codeaurora.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e0ae757c

Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst

+114 −12
Original line number Diff line number Diff line
@@ -27,32 +27,134 @@ these MAP frames and send them to appropriate PDN's. 
2. Packet format

================



a. MAP packet (data / control)

a. MAP packet v1 (data / control)



MAP header has the same endianness of the IP packet.

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

  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

or data packet. Command 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.

Next header is used to indicate the presence of another header, currently is

limited to checksum header.



Padding is number of bytes to be added for 4 byte alignment if required by

hardware.

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 (command specific)::

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
@@ -74,7 +176,7 @@ Command types 
3 is for error during processing of commands

= ==========================================



c. Aggregation

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