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 16:21:35 +0000
From:   Vinod Polimera <vpolimer@....qualcomm.com>
To:     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>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "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



> -----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.

Thanks,
Vinod P.