can, tcan4x5x: look to merge rpi support into rpi kernel tree

[Torin Cooper-Bennun]

On Mon, 15 Feb 2021 at 14:45, Marc Kleine-Budde <mkl at pengutronix.de> wrote:
> Sadly, the driver is still not in good shape...I think it will explode
> as soon as you receive a CAN frame on the rpi, as the frames are passed
> into the networking stack from the wrong context...
>
> Maybe I'll find some time to get receive properly working.

I'm afraid I've just found that myself -- in fact, I'm having problems
getting TX to behave as well. I think the chip configuration is
incorrect (at the very least, the chip is never put into standby mode,
which the datasheet says is paramount!) The current config procedure
ends up with bizarre activity on the CAN lines. I also observed
intermittent refcount warnings during driver use.

I've cherry-picked the relevant changes onto RPi kernel 5.10 :
https://github.com/tcbennun/linux/commit/c32a0d422b551390f6960243f29e1afacfe30d48
and I'll be next trying the bleeding-edge driver with 5.11.

> BTW: what kind of hardware are you using?

This is a Raspberry Pi 3 Model B v1.2, hosting a TCAN4550 on spi0. The
external oscillator for the TCAN4550 is 20 MHz.

Since you've confirmed it needs work, I'll probably be able to put
some time into it myself.

Thanks for getting in touch!

--
Regards,

Torin Cooper-Bennun
www.maxiluxsystems.com | Software Engineer