linux-kernel - Re: [PATCH v3 015/105] drm/vc4: hvs: Boost the core clock during modeset

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Message-ID: <CADaigPUYwmwcFDtH3ZtyDaGWvutAYSX=JuMhXh2EtfNVLU6iDQ@mail.gmail.com>
Date:   Tue, 2 Jun 2020 10:52:21 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v3 015/105] drm/vc4: hvs: Boost the core clock during modeset

On Tue, Jun 2, 2020 at 5:52 AM Maxime Ripard <maxime@...no.tech> wrote:
>
> Hi Eric,
>
> On Wed, May 27, 2020 at 09:33:44AM -0700, Eric Anholt wrote:
> > On Wed, May 27, 2020 at 8:49 AM Maxime Ripard <maxime@...no.tech> wrote:
> > >
> > > In order to prevent timeouts and stalls in the pipeline, the core clock
> > > needs to be maxed at 500MHz during a modeset on the BCM2711.
> >
> > Like, the whole system's core clock?
>
> Yep, unfortunately...
>
> > How is it reasonable for some device driver to crank the system's core
> > clock up and back down to some fixed-in-the-driver frequency? Sounds
> > like you need some sort of opp thing here.
>
> That frequency is the minimum rate of that clock. However, since other
> devices have similar requirements (unicam in particular) with different
> minimum requirements, we will switch to setting a minimum rate instead
> of enforcing a particular rate, so that patch would be essentially
> s/clk_set_rate/clk_set_min_rate/.

clk_set_min_rate makes a lot more sense to me.  r-b with that obvious
change. Thanks!