linux-kernel - Re: [PATCH] thermal/core: Make 'forced

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Date:   Sun, 13 Dec 2020 01:11:05 +0000
From:   Matthew Garrett <mjg59@...on.org.uk>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rui.zhang@...el.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, amitk@...nel.org,
        Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH] thermal/core: Make 'forced_passive' as obsolete candidate

On Sun, Dec 13, 2020 at 12:39:26AM +0100, Daniel Lezcano wrote:
> On 12/12/2020 21:08, Matthew Garrett wrote:
> > Anything that provides a trip point that has no active notifications and
> > doesn't provide any information that tells the kernel to poll it.
> 
> I'm not able to create a setup as you describe working correctly with
> the forced passive trip point.
> 
> The forced passive trip can not be detected as there is no comparison
> with the defined temperature in the thermal_zone_device_update() function.

The logic seems to be in the step_wise thermal governor. I'm not sure
why it would be used in thermal_zone_device_update() - the entire point
is that we don't get updates from the device?

> If my analysis is correct, this 'feature' is broken since years, more
> than 8 years to be exact and nobody complained.

I've no problem with it being removed if there are no users, but in that
case the justification should be rewritten - ACPI table updates aren't a
complete replacement for the functionality offered (and can't be used if
the lockdown LSM is being used in any case).