linux-kernel - Re: [PATCH v4 4/4] arm64/dts/qcom/sm8250: remove assigned-clock-rate property for mdp clk

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Date:   Fri, 4 Mar 2022 03:15:49 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Vinod Polimera <quic_vpolimer@...cinc.com>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robdclark@...il.com,
        dianders@...omium.org, quic_kalyant@...cinc.com
Subject: Re: [PATCH v4 4/4] arm64/dts/qcom/sm8250: remove assigned-clock-rate
 property for mdp clk

On Fri, 4 Mar 2022 at 02:56, Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Dmitry Baryshkov (2022-03-03 15:50:50)
> > On Thu, 3 Mar 2022 at 12:40, Vinod Polimera <quic_vpolimer@...cinc.com> wrote:
> > >
> > > Kernel clock driver assumes that initial rate is the
> > > max rate for that clock and was not allowing it to scale
> > > beyond the assigned clock value.
> > >
> > > Drop the assigned clock rate property and vote on the mdp clock as per
> > > calculated value during the usecase.
> > >
> > > Fixes: 7c1dffd471("arm64: dts: qcom: sm8250.dtsi: add display system nodes")
> >
> > Please remove the Fixes tags from all commits. Otherwise the patches
> > might be picked up into earlier kernels, which do not have a patch
> > adding a vote on the MDP clock.
>
> What patch is that? The Fixes tag could point to that commit.

Please correct me if I'm wrong.
Currently the dtsi enforces bumping the MDP clock when the mdss device
is being probed and when the dpu device is being probed.
Later during the DPU lifetime the core_perf would change the clock's
rate as it sees fit according to the CRTC requirements.

However it would happen only when the during the
dpu_crtc_atomic_flush(), before we call this function, the MDP clock
is left in the undetermined state. The power rails controlled by the
opp table are left in the undetermined state.

I suppose that during the dpu_bind we should bump the clock to the max
possible freq and let dpu_core_perf handle it afterwards.

--
With best wishes
Dmitry