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From:   =?UTF-8?B?Q2zDqW1lbnQgUMOpcm9u?= <peron.clem@gmail.com>
Date:   Mon, 5 Sep 2022 10:28:16 +0200
Message-ID: <CAJiuCceTkz0c6FrGWuEb1589t6EcPoN7aC9Oe4Rxhr-4RCXU9g@mail.gmail.com>
Subject: Re: [PATCH 0/2] opp: core: add regulators enable and disable
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     k.konieczny@samsung.com,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Nishanth Menon <nm@ti.com>, Stephen Boyd <sboyd@kernel.org>,
        Viresh Kumar <vireshk@kernel.org>,
        "open list:ALLWINNER CPUFREQ DRIVER" <linux-pm@vger.kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Rafael Wysocki <rjw@rjwysocki.net>,
        Mark Brown <broonie@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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Hi Viresh,

On Mon, 5 Sept 2022 at 06:35, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 03-09-22, 22:35, Cl=C3=A9ment P=C3=A9ron wrote:
> > Today, I compiled my kernel without any program requiring GPU
> > computing at boot. 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).

>
> > I'm not sure what is the best approach to fix this.
> >
> > Is it required that the dev_pm_opp_set_rate() must be called one time
> > at the GPU driver init?
>
> Right now, Yes. And it looks like the right approach as well.
>
> > Panfost already calls devfreq_recommended_opp() and dev_pm_opp_put()
> > but that doesn't trigger dev_pm_opp_set_rate().
>
> Can you also point to your code ? Which file are you working on ?

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

Regards,
Clement

>
> --
> viresh