Re: [PATCH] thermal/core: Emit a warning if the thermal zone is updated without ops
From: Daniel Lezcano
Date: Tue Dec 08 2020 - 08:52:29 EST
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.
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.
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