linux-kernel - Re: [PATCH 0/2] opp: core: add regulators enable and disable

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Date:   Mon, 5 Sep 2022 15:54:54 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Clément Péron <peron.clem@...il.com>
Cc:     k.konieczny@...sung.com,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        "open list:ALLWINNER CPUFREQ DRIVER" <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Mark Brown <broonie@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] opp: core: add regulators enable and disable

On 05-09-22, 10:28, Clément Péron wrote:
> Hi Viresh,
> 
> On Mon, 5 Sept 2022 at 06:35, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 03-09-22, 22:35, Clément Péron wrote:
> > > Today, I compiled my kernel without any program requiring GPU
> > > computing at boot.

I thought you disabled most of GPU stuff here and so thought panfrost
devfreq will be gone too :)

> > > This makes the dev_pm_opp_set_rate() to never be
> > > called and so the regulator is not enabled before the regulator
> > > framework switches off all the regulators that haven't been enabled.
> > >
> > > Unfortunately switching off the GPU regulator makes my board hang..
> >
> > Why does the board hang? I mean the kernel should boot fine with the
> > GPU disabled, isn't it ? Or is the regulator shared with some other
> > critical resource, or something else.
> 
> The regulator is dedicated to the GPU and the board could certainly
> run without GPU, the issue is that the driver (here panfrost) may do
> some regular access to GPU memory (I suppose).

So we do need GPU to be functional at this point ? i.e. both
clk/regulators should be enabled.

> The code I'm pointing is panfrost_devfreq_init() in
> drivers/gpu/drm/panfrost/panfrost_devfreq.c

I think it would be better to call dev_pm_opp_set_opp() after calling
devfreq_recommended_opp() in this driver, since you already have the
OPP known to you.

-- 
viresh