Re: Trip points crossed not detected when no cooling device bound

Rafael J. Wysocki
2024-06-27T09:55:06Z

On Thu, Jun 27, 2024 at 12:24 AM Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
>
> On 26/06/2024 23:21, Daniel Lezcano wrote:
>
> [ ... ]
>
> >> Oh, I see where the problem can be. If the zone is polling only, it
> >> will not rearm the timer when the current zone temperature is invalid
> >> after the above commit, so does the attached patch help?
> >
> > At this point, I went far when bisecting another problem and I ended up
> > screwing my config file. So I had to generate a new one from the default
> > config. Since then the issue is no longer happening which sounds very
> > strange to me.
> >
> > I'm still investigating but if you have a suggestion coming in mind, it
> > would be welcome because I'm failing to find out what is going on ... :/
>
> I finally reproduced the issue. That happens when there is *no* cooling
> device bound on *any* thermal zones.

Interesting.

> Your patch seems to fix the problem but I'm not sure to understand the
> conditions of the bug

It's probably the same as for commit 202aa0d4bb53:
thermal_zone_device_init() sets tz->temperature to
THERMAL_TEMP_INVALID and if the first invocation of
__thermal_zone_get_temp() returns an error (because the .get_temp()
callback returns an error), monitor_thermal_zone(). If polling is the
only way in which the zone temperature can be updated, things go south
because the timer is not set and there is no other way to set it. No
updates will be coming.

The reason why the presence of cooling devices can "fix" this is
because thermal_bind_cdev_to_trip() sets tz->need_update to 1 which
then causes the thermal_zone_device_update() in
__thermal_cooling_device_register() to trigger and that will update
the temperature.