linux-kernel - Re: [RFC PATCH] cpufreq: dt-platdev: Fix module autoloading

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Message-ID: <87frnl3q63.fsf@minerva.mail-host-address-is-not-set>
Date: Thu, 21 Nov 2024 10:13:40 +0100
From: Javier Martinez Canillas <javierm@...hat.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: robh@...nel.org, arnd@...aro.org, linux-kernel@...r.kernel.org, Radu
 Rendec <rrendec@...hat.com>, Zhipeng Wang <zhipeng.wang_1@....com>, Maxime
 Ripard <mripard@...nel.org>, javier@...hile0.org, "Rafael J. Wysocki"
 <rafael@...nel.org>, linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH] cpufreq: dt-platdev: Fix module autoloading

Viresh Kumar <viresh.kumar@...aro.org> writes:

> On 21-11-24, 09:52, Javier Martinez Canillas wrote:
>> Will autload the driver for any platform that has a Device Tree node with a
>> compatible = "operating-points-v2" (assuming that this node will be a phandle
>> for the "operating-points-v2" property.
>> 
>> For example, in the case of the following DT snippet:
>> 
>> cpus {
>>         cpu@0 {
>>                 operating-points-v2     = <&cpu0_opp_table>;
>>         };
>> };
>> 
>> cpu0_opp_table: opp_table {
>>         compatible = "operating-points-v2";
>> ...
>> };
>> 
>> It will autoload if OF finds the opp_table node, but it register the cpufreq-dt
>> device only if there's a cpu@0 with a "operating-points-v2" property.
>> 
>> Yes, there may be false positives because the autload semantics don't exactly
>> match the criteria for the driver to "match" but I believe is better to load it
>> and not use for those cases, than needing the driver and not autoloading it.
>> 
>> > I am not sure what's the best way forward to fix this.
>> >
>> 
>> I couldn't find another way to solve it, if you have a better idea please let
>> me know. But IMO we should either workaround like this or revert the commit 
>> that changed the driver's Kconfig symbol to be tristate.
>
> Yeah, this needs to be fixed and this patch is one of the ways. Lets see if Arnd
> or Rob have something to add, else can apply this patch.
>

Ok. Please notice though that this is an RFC, since all my arm64 machines have
their own CPUFreq driver and are not using cpufreq-dt-platdev. So I would not
apply it until someone actually tested the patch.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat