linux-kernel - Re: [PATCH] thermal/sysfs: Always enable hysteresis write support

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Date: Wed, 10 Jan 2024 13:49:41 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal/sysfs: Always enable hysteresis write support

On Wed, Jan 10, 2024 at 1:48 PM Manaf Meethalavalappu Pallikunhi
<quic_manafm@...cinc.com> wrote:
>
> Resending to reflect to format
>
> Hi Rafael,
>
> On 1/9/2024 7:12 PM, Rafael J. Wysocki wrote:
> > On Sat, Jan 6, 2024 at 8:16 PM Manaf Meethalavalappu Pallikunhi
> > <quic_manafm@...cinc.com> wrote:
> >> The commit 2e38a2a981b2("thermal/core: Add a generic
> >> thermal_zone_set_trip() function") adds the support to update
> >> trip hysteresis even if set_trip_hyst() operation is not defined.
> >> But during hysteresis attribute creation, if this operation is
> >> defined then only it enables hysteresis write access. It leads
> >> to a case where hysteresis sysfs will be read only for a thermal
> >> zone when its set_trip_hyst() operation is not defined.
> I think it is regression after recent re-work.  If  a sensor  is
> registered witht thermal framework via thermal_of,  sensor driver
> doesn't need to  know the trip configuration and nothing to do with
> set_trip_hyst() in driver. Without this change, if  a sensor needs to be
> monitored from userspace(trip/hysteresis), it is enforcing sensor driver
> to add  dummy set_trip_hyst() operation. Correct me otherwise.
> > Which is by design.
> >
> > For some thermal zone types (eg. acpi), updating trip hysteresis via
> > sysfs might lead to incorrect behavior.
>
> To address this, is it okay to guard hysteresis write permission under
> CONFIG_THERMAL_WRITABLE_TRIPS flag ?

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