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

[Lukasz Luba]

On 12/8/20 2:37 PM, 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.

Some links to point you to such code where sensor has to deal
with protocol and various error reasons [1][2][3]


[1] 
https://elixir.bootlin.com/linux/latest/source/drivers/firmware/arm_scmi/sensors.c#L230
[2] 
https://elixir.bootlin.com/linux/latest/source/drivers/firmware/arm_scmi/driver.c#L425
[3] 
https://elixir.bootlin.com/linux/latest/source/drivers/firmware/arm_scmi/driver.c#L474