iplink_can: add new CAN FD bittiming parameters: Transmitter Delay Compensation ...

iplink_can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC)

At high bit rates, the propagation delay from the TX pin to the RX pin
of the transceiver causes measurement errors: the sample point on the
RX pin might occur on the previous bit.

This issue is addressed in ISO 11898-1 section 11.3.3 "Transmitter
delay compensation" (TDC).

This patch brings command line support to nine TDC parameters which
were recently added to the kernel's CAN netlink interface in order to
implement TDC:
  - IFLA_CAN_TDC_TDCV_MIN: Transmitter Delay Compensation Value
    minimum value
  - IFLA_CAN_TDC_TDCV_MAX: Transmitter Delay Compensation Value
    maximum value
  - IFLA_CAN_TDC_TDCO_MIN: Transmitter Delay Compensation Offset
    minimum value
  - IFLA_CAN_TDC_TDCO_MAX: Transmitter Delay Compensation Offset
    maximum value
  - IFLA_CAN_TDC_TDCF_MIN: Transmitter Delay Compensation Filter
    window minimum value
  - IFLA_CAN_TDC_TDCF_MAX: Transmitter Delay Compensation Filter
    window maximum value
  - IFLA_CAN_TDC_TDCV: Transmitter Delay Compensation Value
  - IFLA_CAN_TDC_TDCO: Transmitter Delay Compensation Offset
  - IFLA_CAN_TDC_TDCF: Transmitter Delay Compensation Filter window

All those new parameters are nested together into the attribute
IFLA_CAN_TDC.

The TDC parameters extend the FD parameters. As such, the TDC
parameters must be specified together the "fd on" flag.

When "fd on" flag is provided, a tdc-mode parameter allows to specify
how to operate.  Valid options for tdc-mode are:

  * auto: the transmitter dynamically measures TDCV for each of the
    transmitted frames. As such, TDCV can not be manually provided. In
    this mode, the user must specify TDCO and may also specify TDCF if
    supported.

  * manual: use a static TDCV provided by the user. In this mode, the
    user must specify both TDCV and TDCO and may also specify TDCF if
    supported.

  * off: TDC is explicitly disabled.

  * tdc-mode parameter omitted (default mode): the kernel decides
    whether TDC should be enabled or not and if so, it calculates the
    TDC values. TDC parameters are an expert option and the average
    user is not expected to provide those, thus the presence of this
    "default mode".

If the fd flag is omitted, all the FD values (including TDC values)
remain unchanged.

If "fd off" flag is specified, all FD values (including TDC values)
are zeroed.

TDCV is always reported in manual mode. In auto mode, TDCV is reported
only if the value is available. Especially, the TDCV might not be
available if the controller has no feature to report it or if the
value in not yet available (i.e. no data sent yet and measurement did
not occur).

TDCF is reported only if tdcf_max is not zero (i.e. if supported by
the controller).

For reference, here are a few samples of how the output looks like:

| $ ip link set can0 type can bitrate 1000000 dbitrate 8000000 fd on tdco 7 tdcf 8 tdc-mode auto

| $ ip --details link show can0
| 1:  can0: <NOARP,ECHO> mtu 72 qdisc noop state DOWN mode DEFAULT group default qlen 10
|     link/can  promiscuity 0 minmtu 0 maxmtu 0
|     can <FD,TDC-AUTO> state STOPPED (berr-counter tx 0 rx 0) restart-ms 0
| 	  bitrate 1000000 sample-point 0.750
| 	  tq 12 prop-seg 29 phase-seg1 30 phase-seg2 20 sjw 1 brp 1
| 	  ES582.1/ES584.1: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp_inc 1
| 	  dbitrate 8000000 dsample-point 0.700
| 	  dtq 12 dprop-seg 3 dphase-seg1 3 dphase-seg2 3 dsjw 1 dbrp 1
| 	  tdco 7 tdcf 8
| 	  ES582.1/ES584.1: dtseg1 2..32 dtseg2 1..16 dsjw 1..8 dbrp 1..32 dbrp_inc 1
| 	  tdco 0..127 tdcf 0..127
| 	  clock 80000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

| $ ip --details --json --pretty link show can0
| [ {
|         "ifindex": 1,
|         "ifname": "can0",
|         "flags": [ "NOARP","ECHO" ],
|         "mtu": 72,
|         "qdisc": "noop",
|         "operstate": "DOWN",
|         "linkmode": "DEFAULT",
|         "group": "default",
|         "txqlen": 10,
|         "link_type": "can",
|         "promiscuity": 0,
|         "min_mtu": 0,
|         "max_mtu": 0,
|         "linkinfo": {
|             "info_kind": "can",
|             "info_data": {
|                 "ctrlmode": [ "FD","TDC-AUTO" ],
|                 "state": "STOPPED",
|                 "berr_counter": {
|                     "tx": 0,
|                     "rx": 0
|                 },
|                 "restart_ms": 0,
|                 "bittiming": {
|                     "bitrate": 1000000,
|                     "sample_point": "0.750",
|                     "tq": 12,
|                     "prop_seg": 29,
|                     "phase_seg1": 30,
|                     "phase_seg2": 20,
|                     "sjw": 1,
|                     "brp": 1
|                 },
|                 "bittiming_const": {
|                     "name": "ES582.1/ES584.1",
|                     "tseg1": {
|                         "min": 2,
|                         "max": 256
|                     },
|                     "tseg2": {
|                         "min": 2,
|                         "max": 128
|                     },
|                     "sjw": {
|                         "min": 1,
|                         "max": 128
|                     },
|                     "brp": {
|                         "min": 1,
|                         "max": 512
|                     },
|                     "brp_inc": 1
|                 },
|                 "data_bittiming": {
|                     "bitrate": 8000000,
|                     "sample_point": "0.700",
|                     "tq": 12,
|                     "prop_seg": 3,
|                     "phase_seg1": 3,
|                     "phase_seg2": 3,
|                     "sjw": 1,
|                     "brp": 1,
|                     "tdc": {
|                         "tdco": 7,
|                         "tdcf": 8
|                     }
|                 },
|                 "data_bittiming_const": {
|                     "name": "ES582.1/ES584.1",
|                     "tseg1": {
|                         "min": 2,
|                         "max": 32
|                     },
|                     "tseg2": {
|                         "min": 1,
|                         "max": 16
|                     },
|                     "sjw": {
|                         "min": 1,
|                         "max": 8
|                     },
|                     "brp": {
|                         "min": 1,
|                         "max": 32
|                     },
|                     "brp_inc": 1,
|                     "tdc": {
|                         "tdco": {
|                             "min": 0,
|                             "max": 127
|                         },
|                         "tdcf": {
|                             "min": 0,
|                             "max": 127
|                         }
|                     }
|                 },
|                 "clock": 80000000
|             }
|         },
|         "num_tx_queues": 1,
|         "num_rx_queues": 1,
|         "gso_max_size": 65536,
|         "gso_max_segs": 65535
|     } ]

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: David Ahern <dsahern@kernel.org>