Re: am335x: 5.18.x: system stalling

[Arnd Bergmann <arnd@arndb.de>]

On Thu, May 19, 2022 at 5:52 PM Yegor Yefremov
<yegorslists@googlemail.com> wrote:
> On Thu, May 12, 2022 at 12:20 PM Yegor Yefremov
> <yegorslists@googlemail.com> wrote:
> > On Thu, May 12, 2022 at 10:43 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > On Thu, May 12, 2022 at 7:41 AM Tony Lindgren <tony@atomide.com> wrote:
> > > > * Yegor Yefremov <yegorslists@googlemail.com> [220511 14:16]:
> > > > > On Thu, May 5, 2022 at 7:08 AM Tony Lindgren <tony@atomide.com> wrote:
> > > > > > * Yegor Yefremov <yegorslists@googlemail.com> [220504 10:35]:
> > > > > > > Hi Tony, all,
> > > > > > >
> > > > > > > since kernel 5.18.x (5.17.x doesn't show this behavior), the system
> > > > > > > stalls as soon as I invoke the following commands (initializing
> > > > > > > USB-to-CAN converter):
> > > > > > >
> > > > > > > slcand -o -s8 -t hw -S 3000000 /dev/ttyUSB0
> > > > > > > ip link set slcan0 up
> > >
> > > Oh, I missed this part at first and only looked at the backtrace.
> > > Which CAN driver
> > > are you using? It's likely a problem in the kernel driver.
> >
> > I am using the slcan driver [1].

Ok, so this is just a serial port based driver, which means the
follow-up question
is what you use for your uart. Is this one of the USB-serial ones or an on-chip
uart? Which driver?

> > > CONFIG_DMA_API_DEBUG is still likely to pinpoint the bug, but I might also
> > > just see it by looking at the right source file.
> >
> > I'll try to get more debug info with CONFIG_DMA_API_DEBUG.
>
> DMA_API_DEBUG showed nothing new. But disabling the CPUfreq driver
> "solved" the problem. I have tried different governors and got these
> two groups:
>
> ondemand, schedutil - cause the problem
> conservative, powersave, performance and userspace - don't cause the problem
>
> So far, I have only seen the same debug output that I've initially
> sent and in most cases, the system stalls without the output.

Ok, so that sounds like it happens when you change the frequency.
I assume this means you are using drivers/cpufreq/omap-cpufreq.c?

When using the usersapce governor, do you see problems when you
manually change the frequency from sysfs?

          Arnd