Date:   Mon, 13 Mar 2023 11:45:41 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, rui.zhang@...el.com,
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        platform-driver-x86@...r.kernel.org,
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        linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
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        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
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Subject: Re: [PATCH v8 01/29] thermal/core: Add a generic
 thermal_zone_get_trip() function


Hi Ido,

On 12/03/2023 13:14, Ido Schimmel wrote:
> On Mon, Oct 03, 2022 at 11:25:34AM +0200, Daniel Lezcano wrote:
>> @@ -1252,9 +1319,10 @@ thermal_zone_device_register_with_trips(const char *type, struct thermal_trip *t
>>   		goto release_device;
>>   
>>   	for (count = 0; count < num_trips; count++) {
>> -		if (tz->ops->get_trip_type(tz, count, &trip_type) ||
>> -		    tz->ops->get_trip_temp(tz, count, &trip_temp) ||
>> -		    !trip_temp)
>> +		struct thermal_trip trip;
>> +
>> +		result = thermal_zone_get_trip(tz, count, &trip);
>> +		if (result)
>>   			set_bit(count, &tz->trips_disabled);
>>   	}
> 
> Daniel, this change makes it so that trip points with a temperature of
> zero are no longer disabled. This behavior was originally added in
> commit 81ad4276b505 ("Thermal: Ignore invalid trip points"). The mlxsw
> driver relies on this behavior - see mlxsw_thermal_module_trips_reset()
> - and with this change I see that the thermal subsystem tries to
> repeatedly set the state of the associated cooling devices to the
> maximum state. Other drivers might also be affected by this.
> 
> Following patch solves the problem for me:
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 55679fd86505..b50931f84aaa 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1309,7 +1309,7 @@ thermal_zone_device_register_with_trips(const char *type, struct thermal_trip *t
>                  struct thermal_trip trip;
>   
>                  result = thermal_zone_get_trip(tz, count, &trip);
> -               if (result)
> +               if (result || !trip.temperature)
>                          set_bit(count, &tz->trips_disabled);
>          }
> 
> Should I submit it or do you have a better idea?

Thanks for reporting this, I think the fix you are proposing is correct 
regarding the previous behavior.

However, I disagree with the commit 81ad4276b505, because it defines the 
zero as an invalid trip point. But some platforms have warming devices, 
when the temperature is too cold, eg 0°C, we enable the warming device 
in order to stay in the functioning temperature range.

Other devices can do the same with negative temperature values.

This feature is not yet upstream and the rework of the trip point should 
allow proper handling of cold trip points.

If you can send the change to fix the regression that would be great.

But keep in mind, the driver is assuming an internal thermal framework 
behavior. The trips_disabled is only to overcome a trip point 
description bug and you should not rely on it as well as not changing 
the trip points on the fly after they are registered.

Actually, the mlxsw driver should just build a valid array of trip 
points without 0°C trip point and pass it to 
thermal_zone_device_register_with_trips(). That would be a proper change 
without relying on a side effect of the thermal trip bug 0°C workaround.



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