Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <cover.aaf2100bd7da4609f8bcb8216247d4b4e4379639.1590594512.git-series.maxime@cerno.tech>
 <1aaadf9a5176591c891622cb00b0c50f42e569dc.1590594512.git-series.maxime@cerno.tech>
 <CADaigPWQdeTd2CGCK-yxq+TAU6xKMVsdZfhSVptn4RSENxpdxg@mail.gmail.com> <20200602125227.fe3mt5jnqd6u4pft@gilmour>
In-Reply-To: <20200602125227.fe3mt5jnqd6u4pft@gilmour>
From:   Eric Anholt <eric@anholt.net>
Date:   Tue, 2 Jun 2020 10:52:21 -0700
Message-ID: <CADaigPUYwmwcFDtH3ZtyDaGWvutAYSX=JuMhXh2EtfNVLU6iDQ@mail.gmail.com>
Subject: Re: [PATCH v3 015/105] drm/vc4: hvs: Boost the core clock during modeset
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-rpi-kernel@lists.infradead.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Tim Gover <tim.gover@raspberrypi.com>,
        Phil Elwell <phil@raspberrypi.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jun 2, 2020 at 5:52 AM Maxime Ripard <maxime@cerno.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@cerno.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!