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Commit ac78a15d authored by Oliver Hartkopp's avatar Oliver Hartkopp Committed by Jonathan Corbet
Browse files

can: Add documentation for CAN FD driver configuration 



With Linux 3.15 the infrastructure for CAN FD hardware drivers had been
introduced into the kernel. Now the M_CAN driver and the peak_usb driver
support CAN FD. Update the documentation to show the latest CAN related
configuration options of 'ip' from iproute2 and describe the CAN FD specific
options to set the data bitrate and protocol version (ISO/non-ISO).

Signed-off-by: default avatarOliver Hartkopp <socketcan@hartkopp.net>
Acked-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 4d732701

Documentation/networking/can.txt

+77 −20
Original line number Diff line number Diff line
@@ -1022,9 +1022,18 @@ solution for a couple of reasons: 
        [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1

          phase-seg2 PHASE-SEG2 [ sjw SJW ] ]



        [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |

        [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1

          dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]



        [ loopback { on | off } ]

        [ listen-only { on | off } ]

        [ triple-sampling { on | off } ]

        [ one-shot { on | off } ]

        [ berr-reporting { on | off } ]

        [ fd { on | off } ]

        [ fd-non-iso { on | off } ]

        [ presume-ack { on | off } ]



        [ restart-ms TIME-MS ]

        [ restart ]
@@ -1178,7 +1187,55 @@ solution for a couple of reasons: 
  The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.

  N.B. CAN FD capable devices can also handle and send legacy CAN frames.



  FIXME: Add details about the CAN FD controller configuration when available.

  When configuring CAN FD capable CAN controllers an additional 'data' bitrate

  has to be set. This bitrate for the data phase of the CAN FD frame has to be

  at least the bitrate which was configured for the arbitration phase. This

  second bitrate is specified analogue to the first bitrate but the bitrate

  setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,

  dsample-point, dsjw or dtq and similar settings. When a data bitrate is set

  within the configuration process the controller option "fd on" can be

  specified to enable the CAN FD mode in the CAN controller. This controller

  option also switches the device MTU to 72 (CANFD_MTU).



  The first CAN FD specification presented as whitepaper at the International

  CAN Conference 2012 needed to be improved for data integrity reasons.

  Therefore two CAN FD implementations have to be distinguished today:



  - ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)

  - non-ISO compliant: The CAN FD implementation following the 2012 whitepaper



  Finally there are three types of CAN FD controllers:



  1. ISO compliant (fixed)

  2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)

  3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)



  The current ISO/non-ISO mode is announced by the CAN controller driver via

  netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).

  The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for

  switchable CAN FD controllers only.



  Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate:



    $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \

                                   dbitrate 4000000 dsample-point 0.8 fd on

    $ ip -details link show can0

    5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \

             mode DEFAULT group default qlen 10

    link/can  promiscuity 0

    can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0

          bitrate 500000 sample-point 0.750

          tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1

          pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \

          brp-inc 1

          dbitrate 4000000 dsample-point 0.800

          dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1

          pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \

          dbrp-inc 1

          clock 80000000



  Example when 'fd-non-iso on' is added on this switchable CAN FD adapter:

   can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0



  6.7 Supported CAN hardware