linux-kernel - Re: [RFC PATCH] thermal/core: Fix trip point crossing events ordering

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Date: Wed, 6 Mar 2024 14:16:21 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: rjw@...ysocki.net, linux-kernel@...r.kernel.org,
 Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
 "open list:THERMAL" <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] thermal/core: Fix trip point crossing events ordering

On 06/03/2024 13:53, Rafael J. Wysocki wrote:
> On Wed, Mar 6, 2024 at 1:43 PM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>
>> On 06/03/2024 13:02, Rafael J. Wysocki wrote:
>>
>> [ ... ]
>>
>>>> +#define for_each_trip_reverse(__tz, __trip)    \
>>>> +       for (__trip = &__tz->trips[__tz->num_trips - 1]; __trip >= __tz->trips ; __trip--)
>>>> +
>>>>    void __thermal_zone_set_trips(struct thermal_zone_device *tz);
>>>>    int thermal_zone_trip_id(const struct thermal_zone_device *tz,
>>>>                            const struct thermal_trip *trip);
>>>> --
>>>
>>> Generally speaking, this is a matter of getting alignment on the
>>> expectations between the kernel and user space.
>>>
>>> It looks like user space expects to get the notifications in the order
>>> of either growing or falling temperatures, depending on the direction
>>> of the temperature change.  Ordering the trips in the kernel is not
>>> practical, but the notifications can be ordered in principle.  Is this
>>> what you'd like to do?
>>
>> Yes
>>
>>> Or can user space be bothered with recognizing that it may get the
>>> notifications for different trips out of order?
>>
>> IMO it is a bad information if the trip points events are coming
>> unordered. The temperature signal is a time related measurements, the
>> userspace should receive thermal information from this signal in the
>> right order. It sounds strange to track the temperature signal in the
>> kernel, then scramble the information, pass it to the userspace and
>> except it to apply some kind of logic to unscramble it.
> 
> So the notifications can be ordered before sending them out, as long
> as they are produced by a single __thermal_zone_device_update() call.
> 
> I guess you also would like the thermal_debug_tz_trip_up/down() calls
> to be ordered, wouldn't you?

Right

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