Re: [PATCH] can: netlink: Fix TDCO calculation using the old data bittiming

[Oliver Hartkopp]

Hello Marc,

On 21.02.24 15:24, Marc Kleine-Budde wrote:
> On 21.02.2024 15:14:02, Oliver Hartkopp wrote:
> > I have an old PCAN USB adapter (Classical CAN) which uses the pcan_usb
> > driver and wanted to set a 50kbit/s bitrate:
> >
> > ip link set can0 up txqueuelen 500 type can bitrate 50000 sjw 4
> >
> > First it complained about the SJW having a higher value than some phase-seg
> > value which was 2.
> >
> > Error: sjw: 4 greater than phase-seg2: 2.
> >
> > I always thought the driver automatically adapts the SJW value to the
> > highest possible and SJW=4 could always be set. Did this change at a certain
> > point?
>
> Yes, that changed with b5a3d0864ee7 ("can: bittiming: can_sjw_check():
> check that SJW is not longer than either Phase Buffer Segment")
>
> See discussion in https://lore.kernel.org/all/20220907103845.3929288-3-mkl@xxxxxxxxxxxxxx/

Ok, thanks.

> > Anyway, then I reduced the given SJW value and the ip command did not give
> > any error message.
> >
> > But finally there was not CAN traffic possible with my "always working
> > setup".
> >
> > I'm running 6.8.0-rc4-00433-g92a355464776 from Linus' tree.
> >
> > Reverting this patch fixed my issue.
>
> But what has the tdco calculation to do with non CAN-FD controllers?

Hm, I was using a Debian 6.1 kernel in between, which worked.

Then I booted my 6.8.0-rc4-00433-g92a355464776 again, reverted the patch 
and loaded the changed can-dev module by hand - which then also worked.

To double check now I was unloading the patched version and using the 
can-dev from /lib/modules again, also works ¯\_(ツ)_/¯

So, I'll have to make more investigations what really went wrong here.
I also was astonished about such CAN FD dependency.

Will come back with more info about my experienced issue.
So far please drop my blame for this patch.

Best regards,
Oliver