linux-kernel - Re: [PATCH] thermal: of: Allow selection of thermal governor in DT

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Message-ID: <6d5aeab8-aafe-fa3b-585e-953a34864e7d@arm.com>
Date:   Tue, 6 Mar 2018 12:32:08 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ram Chandrasekar <rkumbako@...eaurora.org>
Cc:     Amit Kucheria <amit.kucheria@...aro.org>,
        devicetree@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        ilina@...eaurora.org, Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal: of: Allow selection of thermal governor in DT

On 05/03/18 18:36, Amit Kucheria wrote:
> From: Ram Chandrasekar <rkumbako@...eaurora.org>
> 
> There is currently no way for the governor to be selected for each thermal
> zone in devicetree. 

How is that any different from cpufreq, cpuidle or devfreq subsystems ?

> This results in the default governor being used for all
> thermal zones even though no such restriction exists in the core code.
> 

What restrictions ?

> Add support for specifying the thermal governor to be used for a thermal
> zone in the devicetree.

Then what prevents us from doing the same for other subsystems with so
called /inefficient default/ governors ?

> The devicetree config should specify the governor
> name as a string that matches any available governors. If not specified, we
> maintain the current behaviour of using the default governor.

If one is specified, can the user change it from sysfs ? If
yes, then why do we need this binding at all ? If no, we are basically
restricting, then what would happen if the DT was shipped with wrong
governor specified because the firmware author didn't know about any
other governor ?

IMO, having this in DT is bad idea as it may cause more issues than
gain. We already have sysfs support like other PM subsystems and
userspace can deal with it.

-- 
Regards,
Sudeep