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

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Message-ID: <90c0a34a-2640-d6b7-0eb3-19fe789d2998@quicinc.com>
Date: Wed, 10 Jan 2024 18:17:17 +0530
From: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
CC: 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

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 ?

Thanks,

Manaf