linux-kernel - Re: [PATCH v6 1/5] drm/msm/disp/dpu1: set mdp clk to the maximum frequency in opp table during probe

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Date:   Mon, 21 Mar 2022 20:39:59 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Vinod Polimera <vpolimer@....qualcomm.com>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        quic_vpolimer <quic_vpolimer@...cinc.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>
Subject: Re: [PATCH v6 1/5] drm/msm/disp/dpu1: set mdp clk to the maximum
 frequency in opp table during probe

On Mon, 21 Mar 2022 at 19:21, Vinod Polimera <vpolimer@....qualcomm.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Stephen Boyd <swboyd@...omium.org>
> > Sent: Friday, March 18, 2022 2:41 AM
> > To: quic_vpolimer <quic_vpolimer@...cinc.com>;
> > devicetree@...r.kernel.org; dri-devel@...ts.freedesktop.org;
> > freedreno@...ts.freedesktop.org; linux-arm-msm@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org; robdclark@...il.com;
> > dmitry.baryshkov@...aro.org; dianders@...omium.org; quic_kalyant
> > <quic_kalyant@...cinc.com>
> > Subject: Re: [PATCH v6 1/5] drm/msm/disp/dpu1: set mdp clk to the
> > maximum frequency in opp table during probe
> >
> > WARNING: This email originated from outside of Qualcomm. Please be wary
> > of any links or attachments, and do not enable macros.
> >
> > Quoting Vinod Polimera (2022-03-14 07:46:53)
> > > use max clock during probe/bind sequence from the opp table.
> > > The clock will be scaled down when framework sends an update.
> >
> > Capitalize 'use'.
> >
> > Why is it important to use max frequency during probe/bind? Does not
> > setting the clk rate during probe mean that we'll never use the max
> > rate? Does it speed things up during probe?
>
> We need to vote mdp clock during probe/bind so that rails are not set at undetermined state as pointed out by Dmitry.
> Since we dont know what will be the rate set in boot loader, it would be ideal to vote at max frequency.
> There could be a firmware display programmed in bootloader and we want to transition it to kernel without underflowing.

This should be expressed in the commit message.


-- 
With best wishes
Dmitry