Re: [PATCH v3] drm/msm/dp: update is_connected status base on sink count at dp_pm_resume()

[Stephen Boyd <swboyd@chromium.org>]

Quoting Kuogee Hsieh (2021-08-03 09:25:13)
> 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.
>
> Changes in v2:
> -- remove dp_get_sink_count() cand call drm_dp_read_sink_count()
>
> Changes in v3:
> -- delete status local variable from dp_pm_resume()
>
> Fixes: d9aa6571b28ba ("drm/msm/dp: check sink_count before update is_connected status")
> Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 78c5301..0f39256 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1313,7 +1313,7 @@ static int dp_pm_resume(struct device *dev)
>         struct platform_device *pdev = to_platform_device(dev);
>         struct msm_dp *dp_display = platform_get_drvdata(pdev);
>         struct dp_display_private *dp;
> -       u32 status;
> +       int sink_count = 0;
>
>         dp = container_of(dp_display, struct dp_display_private, dp_display);
>
> @@ -1327,14 +1327,26 @@ 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 sink conencted, do dpcd read sink count */

s/conencted/connected/

This also just says what the code is doing. Why do we only read the sink
count if the link is connected? Can we read the sink count even if the
link isn't connected and then consider sink count as 0 if trying to read
fails?

> +       if (dp_catalog_link_is_connected(dp->catalog)) {
> +               sink_count = drm_dp_read_sink_count(dp->aux);
> +               if (sink_count < 0)
> +                       sink_count = 0;
> +       }
>
> +       dp->link->sink_count = sink_count;
>         /*
>          * 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)
> +       if (dp->link->sink_count)
>                 dp->dp_display.is_connected = true;
>         else
>                 dp->dp_display.is_connected = false;