[PATCH] drm/bridge: display-connector: don't set OP_DETECT for DisplayPorts

[PATCH] drm/bridge: display-connector: don't set OP_DETECT for DisplayPorts

[Dmitry Baryshkov]

Detecting the monitor for DisplayPort targets is more complicated than
just reading the HPD pin level: it requires reading the DPCD in order to
check what kind of device is attached to the port and whether there is
an actual display attached.

In order to let DRM framework handle such configurations, disable
DRM_BRIDGE_OP_DETECT for dp-connector devices, letting the actual DP
driver perform detection. This still keeps DRM_BRIDGE_OP_HPD enabled, so
it is valid for the bridge to report HPD events.

Currently inside the kernel there are only two targets which list
hpd-gpios for dp-connector devices: arm64/qcom/qcs6490-rb3gen2 and
arm64/qcom/sa8295p-adp. Both should be fine with this change.

Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Konrad Dybcio <konradybcio@kernel.org>
Cc: linux-arm-msm@vger.kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/display-connector.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/display-connector.c b/drivers/gpu/drm/bridge/display-connector.c
index d7e1c2f8f53cad514ec502d58c1b94d348515b42..e9f16dbc953533c2a2d329ee8fd50c1923a78aac 100644
--- a/drivers/gpu/drm/bridge/display-connector.c
+++ b/drivers/gpu/drm/bridge/display-connector.c
@@ -373,7 +373,8 @@ static int display_connector_probe(struct platform_device *pdev)
 	if (conn->bridge.ddc)
 		conn->bridge.ops |= DRM_BRIDGE_OP_EDID
 				 |  DRM_BRIDGE_OP_DETECT;
-	if (conn->hpd_gpio)
+	/* Detecting the monitor requires reading DPCD */
+	if (conn->hpd_gpio && type != DRM_MODE_CONNECTOR_DisplayPort)
 		conn->bridge.ops |= DRM_BRIDGE_OP_DETECT;
 	if (conn->hpd_irq >= 0)
 		conn->bridge.ops |= DRM_BRIDGE_OP_HPD;

---
base-commit: 82928cc1c2b2be16ea6ee9e23799ca182e1cd37c
change-id: 20250802-dp-conn-no-detect-b901893b5e3c

Best regards,
-- 
With best wishes
Dmitry

Re: [PATCH] drm/bridge: display-connector: don't set OP_DETECT for DisplayPorts

[Laurent Pinchart]

Hi Dmitry,

Thank you for the patch.

On Sat, Aug 02, 2025 at 01:40:35PM +0300, Dmitry Baryshkov wrote:
> Detecting the monitor for DisplayPort targets is more complicated than
> just reading the HPD pin level: it requires reading the DPCD in order to
> check what kind of device is attached to the port and whether there is
> an actual display attached.
> 
> In order to let DRM framework handle such configurations, disable
> DRM_BRIDGE_OP_DETECT for dp-connector devices, letting the actual DP
> driver perform detection. This still keeps DRM_BRIDGE_OP_HPD enabled, so
> it is valid for the bridge to report HPD events.
> 
> Currently inside the kernel there are only two targets which list
> hpd-gpios for dp-connector devices: arm64/qcom/qcs6490-rb3gen2 and
> arm64/qcom/sa8295p-adp. Both should be fine with this change.
> 
> Cc: Bjorn Andersson <andersson@kernel.org>
> Cc: Konrad Dybcio <konradybcio@kernel.org>
> Cc: linux-arm-msm@vger.kernel.org
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Makes sense.

Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

> ---
>  drivers/gpu/drm/bridge/display-connector.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/display-connector.c b/drivers/gpu/drm/bridge/display-connector.c
> index d7e1c2f8f53cad514ec502d58c1b94d348515b42..e9f16dbc953533c2a2d329ee8fd50c1923a78aac 100644
> --- a/drivers/gpu/drm/bridge/display-connector.c
> +++ b/drivers/gpu/drm/bridge/display-connector.c
> @@ -373,7 +373,8 @@ static int display_connector_probe(struct platform_device *pdev)
>  	if (conn->bridge.ddc)
>  		conn->bridge.ops |= DRM_BRIDGE_OP_EDID
>  				 |  DRM_BRIDGE_OP_DETECT;
> -	if (conn->hpd_gpio)
> +	/* Detecting the monitor requires reading DPCD */
> +	if (conn->hpd_gpio && type != DRM_MODE_CONNECTOR_DisplayPort)
>  		conn->bridge.ops |= DRM_BRIDGE_OP_DETECT;
>  	if (conn->hpd_irq >= 0)
>  		conn->bridge.ops |= DRM_BRIDGE_OP_HPD;
> 
> ---
> base-commit: 82928cc1c2b2be16ea6ee9e23799ca182e1cd37c
> change-id: 20250802-dp-conn-no-detect-b901893b5e3c

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/bridge: display-connector: don't set OP_DETECT for DisplayPorts

[Dmitry Baryshkov]

On Sat, 02 Aug 2025 13:40:35 +0300, Dmitry Baryshkov wrote:
> Detecting the monitor for DisplayPort targets is more complicated than
> just reading the HPD pin level: it requires reading the DPCD in order to
> check what kind of device is attached to the port and whether there is
> an actual display attached.
> 
> In order to let DRM framework handle such configurations, disable
> DRM_BRIDGE_OP_DETECT for dp-connector devices, letting the actual DP
> driver perform detection. This still keeps DRM_BRIDGE_OP_HPD enabled, so
> it is valid for the bridge to report HPD events.
> 
> [...]

Applied to drm-misc-next, thanks!

[1/1] drm/bridge: display-connector: don't set OP_DETECT for DisplayPorts
      commit: cb640b2ca54617f4a9d4d6efd5ff2afd6be11f19

Best regards,
-- 
With best wishes
Dmitry