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

[Cunhao Lu]

Hi Marc,

> Is the SoC you're using actually a 'v2' silicon revision? At least on
> the rk3568 the downstream kernel has code to read the revision.

The kernel reports the CAN-FD controller as rk3588v2 rev2.2:

  rockchip_canfd fea60000.can can0: Rockchip-CANFD rk3588v2 rev2.2 (errata 0x0000) found
  rockchip_canfd fea70000.can can1: Rockchip-CANFD rk3588v2 rev2.2 (errata 0x0000) found

Following your earlier feedback, I have changed the v2 series to use
rockchip,rk3588-canfd instead of rockchip,rk3588v2-canfd unless we get
more information about RK3588 CAN-FD errata and SoC silicon revisions
from Rockchip.

> Compile the latest https://github.com/linux-can/can-utils/ and test:
>
> $ cangen can0 -I 2 -Li -Di -p 10 -f -g 1 -c32 -b
> $ cansequence -rv can1 -f

I tested with can0 and can1 directly connected. The CAN clock was
200 MHz, and the interfaces were configured as follows:

  ip link set can0 down
  ip link set can0 type can bitrate 500000 sample-point 0.8 dbitrate 1000000 dsample-point 0.8 fd on
  ip link set can0 up

  ip link set can1 down
  ip link set can1 type can bitrate 500000 sample-point 0.8 dbitrate 1000000 dsample-point 0.8 fd on
  ip link set can1 up

Without BRS, this test ran for 15 minutes without problems:

  cangen can0 -I 2 -Li -Di -p 10 -f -g 1 -c32

With BRS enabled:

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

the test only worked when dbitrate was equal to bitrate, for example
with both set to 1M. If dbitrate differed from bitrate, the
controller went bus-off immediately.

So my current conclusion is that CAN-FD itself works on RK3588, but the
support appears incomplete: using a faster data phase with BRS does not
work in my setup.

This looks different from the issue described by the current
RKCANFD_QUIRK_CANFD_BROKEN comment. That quirk is about specific
CAN-FD frames triggering Error Interrupt or Error-Warning during
reception. In my test the non-BRS CAN-FD frames work, while the failure
is tied to using BRS with a data bitrate different from the nominal
bitrate, which immediately drives the controller bus-off.

Given this result, should I still keep CAN-FD disabled for RK3588, or is
it acceptable to enable CAN-FD but document that BRS with a faster data
phase is currently not working?

Thanks,
Cunhao Lu