linux-kernel - Re: [PATCH 3/9] arm64: dts: qcom: sc7280: Enable MDP turbo mode

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Message-ID: <CAD=FV=XJVFX-GkL-wiAoi=r6tdiDHkJ_aFSpx6FE6+gFT5xJjA@mail.gmail.com>
Date: Mon, 26 Feb 2024 07:56:09 -0800
From: Doug Anderson <dianders@...omium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Bjorn Andersson <quic_bjorande@...cinc.com>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, cros-qcom-dts-watchers@...omium.org, 
	Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH 3/9] arm64: dts: qcom: sc7280: Enable MDP turbo mode

Hi,

On Thu, Feb 22, 2024 at 9:32 AM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On Thu, 22 Feb 2024 at 17:04, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
> >
> > On Thu, Feb 22, 2024 at 11:46:26AM +0200, Dmitry Baryshkov wrote:
> > > On Thu, 22 Feb 2024 at 11:28, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
> > > >
> > > >
> > > >
> > > > On 2/22/24 10:04, Dmitry Baryshkov wrote:
> > > > > On Thu, 22 Feb 2024 at 10:56, Konrad Dybcio <konrad.dybcio@...aroorg> wrote:
> > > > >>
> > > > >>
> > > > >>
> > > > >> On 2/22/24 00:41, Dmitry Baryshkov wrote:
> > > > >>> On Thu, 22 Feb 2024 at 01:19, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
> > > > >>>>
> > > > >>>> The max frequency listed in the DPU opp-table is 506MHz, this is not
> > > > >>>> sufficient to drive a 4k@60 display, resulting in constant underrun.
> > > > >>>>
> > > > >>>> Add the missing MDP_CLK turbo frequency of 608MHz to the opp-table to
> > > > >>>> fix this.
> > > > >>>
> > > > >>> I think we might want to keep this disabled for ChromeOS devices. Doug?
> > > > >>
> > > > >> ChromeOS devices don't get a special SoC
> > > > >
> > > > > But they have the sc7280-chrome-common.dtsi, which might contain a
> > > > > corresponding /delete-node/ .
> > > >
> > > > What does that change? The clock rates are bound to the
> > > > SoC and the effective values are limited by link-frequencies
> > > > or the panel driver.
> > >
> > > Preventing the DPU from overheating? Or spending too much power?
> > >
> >
> > Perhaps I'm misunderstanding the implementation then, are we always
> > running at the max opp? I thought the opp was selected based on the
> > current need for performance?
>
> Yes. My concern was whether the Chrome people purposely skipped this
> top/turbo freq for any reason. In such a case, surprising them by
> adding it to all platforms might be not the best idea. I hope Doug can
> comment here.

Thanks for thinking of us! In this case, I think the only users left
of the sc7280 Chrome devices are folks like Rob and then a few folks
on Qualcomm's display team (like Abhinav), so if they're happy with
the change then I have no objections.

In any case, I'm not aware of any reason why this would have been
skipped for Chrome. The Chrome devices were always intended to support
4K so I assume this was an oversight and nothing more. ...of course,
as Abhinav points out Chrome devices are currently limited to HBR2 + 2
lanes DP so they can't go 4K60 anyway.

In any case, in case it matters, feel free to have:

Acked-by: Douglas Anderson <dianders@...omium.org>