linux-kernel - Re: R: [RFC PATCH v3 0/2] Add Krait Cache Scaling support

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Message-ID: <20200903065314.y3ynhwydahaeg6o6@vireshk-i7>
Date:   Thu, 3 Sep 2020 12:23:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     ansuelsmth@...il.com
Cc:     'Sibi Sankar' <sibis@...eaurora.org>, vincent.guittot@...aro.org,
        saravanak@...gle.com, 'Sudeep Holla' <sudeep.holla@....com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        'Rob Herring' <robh+dt@...nel.org>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: R: [RFC PATCH v3 0/2] Add Krait Cache Scaling support

On 31-08-20, 09:41, ansuelsmth@...il.com wrote:
> On 31-08-20, Sibi wrote:
> > On 2020-08-24 16:10, Viresh Kumar wrote:
> > > +Vincent/Saravana/Sibi
> > >
> > > On 21-08-20, 16:00, Ansuel Smith wrote:
> > >> This adds Krait Cache scaling support using the cpufreq notifier.
> > >> I have some doubt about where this should be actually placed (clk or
> > >> cpufreq)?
> > >> Also the original idea was to create a dedicated cpufreq driver (like
> > >> it's done in
> > >> the codeaurora qcom repo) by copying the cpufreq-dt driver and adding
> > >> the cache
> > >> scaling logic but i still don't know what is better. Have a very
> > >> similar driver or
> > >> add a dedicated driver only for the cache using the cpufreq notifier
> > >> and do the
> > >> scale on every freq transition.
> > >> Thanks to everyone who will review or answer these questions.
> > >
> > > Saravana was doing something with devfreq to solve such issues if I
> > > wasn't mistaken.
> > >
> > > Sibi ?
> > 
> > IIRC the final plan was to create a devfreq device
> > and devfreq-cpufreq based governor to scale them, this
> > way one can switch to a different governor if required.
> 
> So in this case I should convert this patch to a devfreq driver- 

I think this should happen nevertheless. You are doing DVFS for a
device which isn't a CPU and devfreq looks to be the right place of
doing so.

> Isn't overkill to use a governor for such a task?
> (3 range based on the cpufreq?)

I am not sure about the governor part here, maybe it won't be required
?

-- 
viresh