linux-kernel - Re: [PATCH v2] drm/msm/dp: correct 1.62G link rate at dp_catalog_ctrl_config

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Date:   Wed, 24 Aug 2022 12:30:38 -0500
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, dmitry.baryshkov@...aro.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/msm/dp: correct 1.62G link rate at dp_catalog_ctrl_config_msa()

Quoting Kuogee Hsieh (2022-08-24 10:22:31)
> At current implementation there is an extra 0 at 1.62G link rate which cause
> no correct pixel_div selected for 1.62G link rate to calculate mvid and nvid.
> This patch delete the extra 0 to have mvid and nvid be calculated correctly.
>
> Changes in v2:
> -- fix Fixes tag's text
>
> Fixes: 937f941ca06f  ("drm/msm/dp: Use qmp phy for DP PLL and PHY")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> eviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>

Missing an R.

>
> diff --git a/drivers/gpu/drm/msm/dp/dp_catalog.c b/drivers/gpu/drm/msm/dp/dp_catalog.c
> index 7257515..676279d 100644
> --- a/drivers/gpu/drm/msm/dp/dp_catalog.c
> +++ b/drivers/gpu/drm/msm/dp/dp_catalog.c
> @@ -431,7 +431,7 @@ void dp_catalog_ctrl_config_msa(struct dp_catalog *dp_catalog,
>
>         if (rate == link_rate_hbr3)
>                 pixel_div = 6;
> -       else if (rate == 1620000 || rate == 270000)
> +       else if (rate == 162000 || rate == 270000)

BTW

  $ git grep 162000 -- drivers/gpu/drm/msm/dp/
  drivers/gpu/drm/msm/dp/dp_catalog.c:    else if (rate == 1620000 ||
rate == 270000)
  drivers/gpu/drm/msm/dp/dp_ctrl.c:
ctrl->link->link_params.rate = 162000;
  drivers/gpu/drm/msm/dp/dp_ctrl.c:       case 162000:

We really should have a #define for these things. Can you send a
different followup patch that makes something like HBR3_KHZ, HBR2_KHZ,
etc. and then replaces these bare numbers throughout the driver? That
would prevent this from happening again. This one liner can and should
be backported to stable trees.