Re: [PATCH 2/3] can: rockchip: add RK3588 CAN-FD support

[Cunhao Lu]

Hi Marc,

> Then CAN-FD is broken. :/
>
> Maybe in a later patch we can hack something, to allow working
> configurations.

I did some more tests and found that the immediate bus-off with BRS is
related to the transmit delay compensation setting.

After setting RKCANFD_REG_TRANSMIT_DELAY_COMPENSATION to 0, i.e.
disabling TDC, CAN-FD with BRS works on RK3588 in my setup. I tested the
same command with 500 kbit/s arbitration bitrate and 1, 3 and 5 Mbit/s
data bitrate.

The 5 Mbit/s data phase test setup was:

  CAN clock: 300 MHz
  can0 <-> can1 directly connected
  no other devices on the bus
  bus termination: 60 Ohm

  ip link set can0 type can bitrate 500000 sample-point 0.8 dbitrate 5000000 dsample-point 0.8 fd on berr-reporting on
  ip link set can1 type can bitrate 500000 sample-point 0.8 dbitrate 5000000 dsample-point 0.8 fd on berr-reporting on

  cangen can0 -I 2 -Li -Di -p 10 -f -g 1 -c32 -b
  cansequence -rv can1 -f

The test ran for 15 minutes. The receiver reported continuous sequence
wrap-around messages, e.g.:

  sequence wrap around (0)
  sequence wrap around (1)
  ...
  sequence wrap around (37218)
  sequence wrap around (37219)

The interface statistics after the test were:

  can0:
            re-started bus-errors arbit-lost error-warn error-pass bus-off
            0          0          0          0          0          0
      RX:  bytes packets errors dropped  missed   mcast
       150667356 9528377      0       0       0       0
      TX:  bytes packets errors dropped carrier collsns
       150667356 9528377      0       0       0       0

  can1:
            re-started bus-errors arbit-lost error-warn error-pass bus-off
            0          0          0          0          0          0
      RX:  bytes packets errors dropped  missed   mcast
       150667356 9528377      0       0       0       0
      TX:  bytes packets errors dropped carrier collsns
               0       0      0       0       0       0

There were no bus errors and no bus-off events in this test.

> Can you update the description of the quirk for the rk3588 and add how
> to reproduce it?

With TDC disabled I cannot reproduce the BRS bus-off problem anymore.
This also looks different from RKCANFD_QUIRK_CANFD_BROKEN, so I do not
think RK3588 should use that quirk.

> Please keep it disabled for now.

Given the new test result, I plan to send v4 with the RK3588 TDC register
set to 0 and CAN-FD enabled for RK3588.

Regards,
Cunhao