linux-kernel - Re: [PATCH v5] drivers: thermal: clear all mitigation when thermal zone is disabled

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Message-ID: <4024218b-7938-e181-f456-bff4b3fb157a@arm.com>
Date:   Mon, 31 Jan 2022 07:25:33 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zhang Rui <rui.zhang@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Amit Kucheria <amitk@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v5] drivers: thermal: clear all mitigation when thermal
 zone is disabled

Hi Manaf,

On 1/27/22 6:11 PM, Manaf Meethalavalappu Pallikunhi wrote:
> Whenever a thermal zone is in trip violated state, there is a chance
> that the same thermal zone mode can be disabled either via
> thermal core API or via thermal zone sysfs. Once it is disabled,
> the framework bails out any re-evaluation of thermal zone. It leads
> to a case where if it is already in mitigation state, it will stay
> the same state forever.
> 
> To avoid above mentioned issue, add support to bind/unbind
> governor from thermal zone during thermal zone mode change request
> and clear all existing throttling in governor unbind_from_tz()
> callback.

I have one use case:
This would be a bit dangerous, e.g. to switch governors while there is a
high temperature. Although, sounds reasonable to left a 'default' state
for a next governor.

> 
> Suggested-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> Signed-off-by: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
> ---
>   drivers/thermal/gov_power_allocator.c |  3 +++
>   drivers/thermal/gov_step_wise.c       | 26 ++++++++++++++++++++++++++
>   drivers/thermal/thermal_core.c        | 31 +++++++++++++++++++++++++++----
>   3 files changed, 56 insertions(+), 4 deletions(-)

Why only two governors need that change and not all?
Because they don't have 'bind/unbind' callbacks, then maybe we should
change that as well to make it consistent?

Regards,
Lukasz