linux-kernel - Re: [PATCH v3 3/8] drm/msm/dp: Read DPCD and sink count in bridge detect()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d826de45-f00c-4af8-947b-246362c2be23@oss.qualcomm.com>
Date: Thu, 15 Jan 2026 10:19:27 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov
 <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jessica Zhang <jessica.zhang@....qualcomm.com>
Subject: Re: [PATCH v3 3/8] drm/msm/dp: Read DPCD and sink count in bridge
 detect()

On 1/15/26 8:29 AM, Dmitry Baryshkov wrote:
> From: Jessica Zhang <jessica.zhang@....qualcomm.com>
> 
> Instead of relying on the link_ready flag to specify if DP is connected,
> read the DPCD bits and get the sink count to accurately detect if DP is
> connected.
> 
> Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 60 +++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/msm/dp/dp_drm.c     | 20 -------------
>  drivers/gpu/drm/msm/dp/dp_drm.h     |  2 ++
>  3 files changed, 62 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 5997cd28ba11..a05144de3b93 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1151,6 +1151,66 @@ static int msm_dp_hpd_event_thread_start(struct msm_dp_display_private *msm_dp_p
>  	return 0;
>  }
>  
> +/**
> + * msm_dp_bridge_detect - callback to determine if connector is connected
> + * @bridge: Pointer to drm bridge structure
> + * @connector: Pointer to drm connector structure
> + * Returns: Bridge's 'is connected' status
> + */
> +enum drm_connector_status msm_dp_bridge_detect(struct drm_bridge *bridge,
> +					       struct drm_connector *connector)
> +{
> +	struct msm_dp_bridge *msm_dp_bridge = to_dp_bridge(bridge);
> +	struct msm_dp *dp = msm_dp_bridge->msm_dp_display;
> +	struct msm_dp_display_private *priv;
> +	int ret = 0;
> +	int status = connector_status_disconnected;
> +	u8 dpcd[DP_RECEIVER_CAP_SIZE];
> +	struct drm_dp_desc desc;

Reverse-Christmas-tree would be nice 

> +
> +	dp = to_dp_bridge(bridge)->msm_dp_display;
> +
> +	priv = container_of(dp, struct msm_dp_display_private, msm_dp_display);
> +
> +	if (!dp->link_ready)
> +		return status;
> +
> +	msm_dp_aux_enable_xfers(priv->aux, true);
> +
> +	ret = pm_runtime_resume_and_get(&dp->pdev->dev);
> +	if (ret) {

See ef8057b07c72 ("PM: runtime: Wrapper macros for ACQUIRE()/ACQUIRE_ERR()")


> +		DRM_ERROR("failed to pm_runtime_resume\n");
> +		msm_dp_aux_enable_xfers(priv->aux, false);
> +		return status;
> +	}
> +
> +	ret = msm_dp_aux_is_link_connected(priv->aux);
> +	if (dp->internal_hpd && !ret)
> +		goto end;
> +
> +	ret = drm_dp_read_dpcd_caps(priv->aux, dpcd);


> +	if (ret)
> +		goto end;
> +
> +	ret = drm_dp_read_desc(priv->aux, &desc, drm_dp_is_branch(dpcd));
> +	if (ret)
> +		goto end;
> +
> +	status = connector_status_connected;
> +	if (drm_dp_read_sink_count_cap(connector, dpcd, &desc)) {
> +		int sink_count = drm_dp_read_sink_count(priv->aux);
> +
> +		drm_dbg_dp(dp->drm_dev, "sink_count = %d\n", sink_count);
> +
> +		if (sink_count <= 0)
> +			status = connector_status_disconnected;

< 0 would be an error coming from drm_dp_dpcd_read_byte, should we log
it?

Konrad