am335x: 5.18.x: system stalling

[Yegor Yefremov]

Hi Arnd,

On Sat, May 21, 2022 at 9:41 PM Arnd Bergmann <arnd at arndb.de> wrote:
>
> On Thu, May 19, 2022 at 5:52 PM Yegor Yefremov
> <yegorslists at googlemail.com> wrote:
> > On Thu, May 12, 2022 at 12:20 PM Yegor Yefremov
> > <yegorslists at googlemail.com> wrote:
> > > On Thu, May 12, 2022 at 10:43 AM Arnd Bergmann <arnd at arndb.de> wrote:
> > > >
> > > > On Thu, May 12, 2022 at 7:41 AM Tony Lindgren <tony at atomide.com> wrote:
> > > > > * Yegor Yefremov <yegorslists at googlemail.com> [220511 14:16]:
> > > > > > On Thu, May 5, 2022 at 7:08 AM Tony Lindgren <tony at atomide.com> wrote:
> > > > > > > * Yegor Yefremov <yegorslists at 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?

This is the following chain: am335x -> musb-> ftdi_sio (FT-X flavor).

I have also tried another system with two FT4232 chips (RS232 devices)
and performed transmission tests. This had no effect, the system
didn't stall.

> > > > 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?

Yes.

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

No, I can switch between 300MHz and 600MHz and perform CAN tests.
Everything goes well.

Yegor