linux-kernel - Re: [PATCH] drm/msm/dp: update is_connected status base on sink count at dp_pm

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Date:   Fri, 30 Jul 2021 11:57:24 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <khsieh@...eaurora.org>, agross@...nel.org,
        bjorn.andersson@...aro.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org
Cc:     abhinavk@...eaurora.org, aravindh@...eaurora.org,
        freedreno@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: update is_connected status base on sink count
 at dp_pm_resume()

Quoting Kuogee Hsieh (2021-07-28 14:30:54)
> Currently at dp_pm_resume() is_connected state is decided base on hpd connection
> status only. This will put is_connected in wrongly "true" state at the scenario
> that dongle attached to DUT but without hmdi cable connecting to it. Fix this
> problem by adding read sink count from dongle and decided is_connected state base
> on both sink count and hpd connection status.
>

Please add a Fixes tag.

> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 2b660e9..9bcb261 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1308,6 +1308,17 @@ static int dp_display_remove(struct platform_device *pdev)
>         return 0;
>  }
>
> +static int dp_get_sink_count(struct dp_display_private *dp)
> +{
> +       u8 sink_count;
> +
> +       sink_count = drm_dp_read_sink_count(dp->aux);

drm_dp_read_sink_count() returns an int, not a u8. Comparing a u8 to
less than zero doesn't make any sense as it isn't signed.

> +       if (sink_count < 0)
> +               return 0;
> +
> +       return sink_count;
> +}

We can drop this function and just have an int count in dp_pm_resume()
that is compared to < 0 and then ignored.

> +
>  static int dp_pm_resume(struct device *dev)
>  {
>         struct platform_device *pdev = to_platform_device(dev);
> @@ -1327,14 +1338,22 @@ static int dp_pm_resume(struct device *dev)
>
>         dp_catalog_ctrl_hpd_config(dp->catalog);
>
> -       status = dp_catalog_link_is_connected(dp->catalog);
> +       /*
> +        * set sink to normal operation mode -- D0
> +        * before dpcd read
> +        */
> +       dp_link_psm_config(dp->link, &dp->panel->link_info, false);
>
> +       if ((status = dp_catalog_link_is_connected(dp->catalog)))
> +               dp->link->sink_count = dp_get_sink_count(dp);

Do we need to call drm_dp_read_sink_count_cap() as well?

> +       else
> +               dp->link->sink_count = 0;
>         /*
>          * can not declared display is connected unless
>          * HDMI cable is plugged in and sink_count of
>          * dongle become 1
>          */
> -       if (status && dp->link->sink_count)

Is 'status' used anymore? If not, please remove it.

> +       if (dp->link->sink_count)
>                 dp->dp_display.is_connected = true;
>         else
>                 dp->dp_display.is_connected = false;