Broken watchdog in u-boot master branch

[Pali Rohár]

On Monday 10 October 2022 13:40:38 Tom Rini wrote:
> On Mon, Oct 10, 2022 at 07:22:56PM +0200, Pali Rohár wrote:
> > On Monday 10 October 2022 12:28:18 Tom Rini wrote:
> > > On Sun, Oct 09, 2022 at 09:12:25PM +0200, Pali Rohár wrote:
> > > > Hello! Watchdog code seems to be broken in u-boot master branch.
> > > > On Nokia N900 I'm getting following message in qemu:
> > > > 
> > > > cyclic function rx51_watchdog took too long: 10000us vs 1000us max, disabling
> > > > 
> > > > Seems that watchdog core code is not prepared for "slower" watchdogs
> > > > which communicate over slower i2c bus, like it is the case for N900.
> > > > 
> > > > Disabling slower watchdog is a bad idea as it would result in reboot
> > > > loop instead of slower - but working code.
> > > 
> > > So, looking at this in more detail, we have
> > > CONFIG_CYCLIC_MAX_CPU_TIME_US as a configuration option (which is where
> > > the too long comes from). And picking a random CI run:
> > > https://source.denx.de/u-boot/u-boot/-/jobs/511177
> > > I do see we hit this in CI once, but not every time, QEMU runs here. Is
> > > that the max time is configurable enough to satisfy your concerns here?
> > 
> > It is needed to investigate, how to _properly_ fix this issue, not just
> > workarounded it. Probably other boards may be affected.
> 
> So it's the cyclic watchdog code, which we merged as early as possible
> that's the reason here. And it was merged as early as we could to see if
> there's problems. Are there problems? We're seeing "system too slow,
> disabling" on QEMU, sometimes, and the value of too slow is
> configurable. I know you reported other problems with n900 HW, so we
> can't see if it's failing there

I was tested it with older asm code (as described in that other email,
via git checkout commit -- file) on n900 HW and watchdog problem is
there too. Phone reboots in about 20 seconds. But as I do not have
serial console, I do not know if that "disabling" message is printed
there too (but I guess it is).

> and I don't have any omap3 HW setup in
> my lab atm, just newer generation boards and don't see the problem
> there. Which is why I'm asking, is being able to configure the "too
> slow" value enough? Or is there something else that needs to be done?