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

[Lukasz Luba]

On 12/8/20 3:19 PM, Daniel Lezcano wrote:
> On 08/12/2020 15:37, Lukasz Luba wrote:
> > 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.
>
> Hmm, right. I agree with your point.
>
> What about the following changes:
>
>   - Add the new APIs:
>
>     thermal_zone_device_critical(struct thermal_zone_device *tz);
>       => emergency poweroff
>
>     thermal_zone_device_hot(struct thermal_zone_device *tz);
>       => userspace notification

They look promising, I have to look into the existing code.
When they would be called?

>   - Add a big fat WARN when thermal_zone_device_update is called with
> .get_temp == NULL because that must not happen.

Good idea

> If the .get_temp is NULL it is because we only have a HOT/CRITICAL
> thermal trip points where we don't care about the temperature and
> governor decision, right ?

That is a good question. Let me dig into the code. I would say yes - we
don't have to hassle with governor in this circumstances.