linux-kernel - Re: [PATCH v4 1/4] drm/msm/dp: check sink_count before update is

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Date:   Mon, 3 May 2021 21:30:44 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <khsieh@...eaurora.org>, robdclark@...il.com,
        sean@...rly.run
Cc:     abhinavk@...eaurora.org, aravindh@...eaurora.org, airlied@...ux.ie,
        daniel@...ll.ch, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] drm/msm/dp: check sink_count before update
 is_connected status

Quoting Kuogee Hsieh (2021-04-21 16:37:35)
> Link status is different from display connected status in the case
> of something like an Apple dongle where the type-c plug can be
> connected, and therefore the link is connected, but no sink is
> connected until an HDMI cable is plugged into the dongle.
> The sink_count of DPCD of dongle will increase to 1 once an HDMI
> cable is plugged into the dongle so that display connected status
> will become true. This checking also apply at pm_resume.
>
> Changes in v4:
> -- none
>
> Fixes: 94e58e2d06e3 ("drm/msm/dp: reset dp controller only at boot up and pm_resume")
> Reported-by: Stephen Boyd <swboyd@...omium.org>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Tested-by: Stephen Boyd <swboyd@...omium.org>
> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 5a39da6..0ba71c7 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -586,10 +586,8 @@ static int dp_connect_pending_timeout(struct dp_display_private *dp, u32 data)
>         mutex_lock(&dp->event_mutex);
>
>         state = dp->hpd_state;
> -       if (state == ST_CONNECT_PENDING) {
> -               dp_display_enable(dp, 0);
> +       if (state == ST_CONNECT_PENDING)
>                 dp->hpd_state = ST_CONNECTED;
> -       }

This part has been there since commit 8ede2ecc3e5e ("drm/msm/dp: Add DP
compliance tests on Snapdragon Chipsets") so we should add that tag here
too, like

Fixes: 8ede2ecc3e5e ("drm/msm/dp: Add DP compliance tests on
Snapdragon Chipsets")

It would also be nice if this hunk was explained. It doesn't make sense
to me that a timeout would enable the display so maybe that can be
called out in the commit text about why we remove the call here.