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

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Message-ID: <14651d5b-0f67-4bff-b699-2cd1601b4fb2@linaro.org>
Date: Wed, 6 Mar 2024 13:43:00 +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 13:02, 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.

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