linux-kernel - Re: [PATCH v2 2/2] drm/msm/disp/dpu1: set mdp clk to the maximum frequency in opp table

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Date:   Fri, 25 Feb 2022 10:12:40 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Vinod Polimera <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,
        dianders@...omium.org, quic_kalyant@...cinc.com
Subject: Re: [PATCH v2 2/2] drm/msm/disp/dpu1: set mdp clk to the maximum
 frequency in opp table

Quoting Vinod Polimera (2022-02-25 07:57:50)
> use max clock during resume sequence from the opp table.

s/use/Use/

> The clock will be scaled down when framework sends an update.
>
> Fixes: 62fbdce91("arm64: dts: qcom: sc7280: add display dt nodes")

Presumably this is the wrong fixes tag, see below.

>
> Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> index d550f90..3288f52 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> @@ -1319,6 +1319,7 @@ static int __maybe_unused dpu_runtime_resume(struct device *dev)
>         struct drm_device *ddev;
>         struct dss_module_power *mp = &dpu_kms->mp;
>         int i;
> +       unsigned long max_freq = ULONG_MAX;
>
>         ddev = dpu_kms->dev;
>
> @@ -1333,6 +1334,8 @@ static int __maybe_unused dpu_runtime_resume(struct device *dev)
>                 return rc;
>         }
>
> +       dev_pm_opp_find_freq_floor(dev, &max_freq);

This isn't exactly a cheap thing to do every runtime resume. Please get
the max frequency during probe and stash it somewhere to avoid making
this call over and over again.

> +       dev_pm_opp_set_rate(dev, max_freq);

This is entirely new. The assigned clock rates from DT aren't set during
runtime resume, only during device probe. My question is, if this is
needed now then does it mean we've been running the clk at low speed
after the first runtime suspend and never been pushing it back up again?

>         dpu_vbif_init_memtypes(dpu_kms);
>
>         drm_for_each_encoder(encoder, ddev)