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

[Viresh Kumar]

On 05-09-22, 10:28, Clément Péron wrote:
> Hi Viresh,
> 
> On Mon, 5 Sept 2022 at 06:35, Viresh Kumar <viresh.kumar@xxxxxxxxxx> 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