Re: [PATCH] thermal/core: Emit a warning if the thermal zone is updated without ops

[Lukasz Luba]

On 12/8/20 1:51 PM, Daniel Lezcano wrote:
> Hi Lukasz,
>
> On 08/12/2020 10:36, Lukasz Luba wrote:
> > Hi Daniel,
>
> [ ... ]
>
> > >      static void thermal_zone_device_init(struct thermal_zone_device *tz)
> > > @@ -553,11 +555,9 @@ void thermal_zone_device_update(struct
> > > thermal_zone_device *tz,
> > >        if (atomic_read(&in_suspend))
> > >            return;
> > >    -    if (!tz->ops->get_temp)
> > > +    if (update_temperature(tz))
> > >            return;
> > >    -    update_temperature(tz);
> > > -
> >
> > I think the patch does a bit more. Previously we continued running the
> > code below even when the thermal_zone_get_temp() returned an error (due
> > to various reasons). Now we stop and probably would not schedule next
> > polling, not calling:
> > handle_thermal_trip() and monitor_thermal_zone()
>
> I agree there is a change in the behavior.
>
> > I would left update_temperature(tz) as it was and not check the return.
> > The function thermal_zone_get_temp() can protect itself from missing
> > tz->ops->get_temp(), so we should be safe.
> >
> > What do you think?
>
> Does it make sense to handle the trip point if we are unable to read the
> temperature?
>
> The lines following the update_temperature() are:
>
>   - thermal_zone_set_trips() which needs a correct tz->temperature
>
>   - handle_thermal_trip() which needs a correct tz->temperature to
> compare with
>
>   - monitor_thermal_zone() which needs a consistent tz->passive. This one
> is updated by the governor which is in an inconsistent state because the
> temperature is not updated.
>
> The problem I see here is how the interrupt mode and the polling mode
> are existing in the same code path.
>
> The interrupt mode can call thermal_notify_framework() for critical/hot
> trip points without being followed by a monitoring. But for the other
> trip points, the get_temp is needed.

Yes, I agree that we can bail out when there is no .get_temp() callback
and even not schedule next polling in such case.
But I am just not sure if we can bail out and not schedule the next
polling, when there is .get_temp() populated and the driver returned
an error only at that moment, e.g. indicating some internal temporary,
issue like send queue full, so such as -EBUSY, or -EAGAIN, etc.
The thermal_zone_get_temp() would pass the error to update_temperature()
but we return, losing the next try. We would not check the temperature
again.

> IMHO, we should return if update_temperature() is failing.
>
> Perhaps, it would make sense to simply prevent to register a thermal
> zone if the get_temp ops is not defined.
>
> AFAICS, if the interrupt mode without get_temp callback are for hot and
> critical trip points which can be directly invoked from the sensor via a
> specified callback, no thermal zone would be needed in this case.