drm/bridge: display-connector: detect DP state if cable is plugged on boot

[PATCH 2/2] drm/bridge: display-connector: trigger initial HPD event for DP

Posted by Dmitry Baryshkov 3 weeks, 3 days ago

If the DisplayPort drivers use display-connector for the HPD detection,
the internal HPD state machine might be not active and thus the hardware
might be not able to handle cable detection correctly. Instead it will
depend on the externall HPD notifications to set the cable state,
bypassing the internal HPD state machine (for example this is the case
for the msm DP driver).

However if the cable has been plugged before the HPD IRQ has been
enabled, there will be no HPD event coming. The drivers might fail
detection in such a case. Trigger the HPD notification after enabling
the HPD IRQ, propagating the cable insertion state.

Fixes: 2e2bf3a5584d ("drm/bridge: display-connector: add DP support")
Reported-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/display-connector.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/bridge/display-connector.c b/drivers/gpu/drm/bridge/display-connector.c
index 6bb1134f75c3..f7a5bfd9c075 100644
--- a/drivers/gpu/drm/bridge/display-connector.c
+++ b/drivers/gpu/drm/bridge/display-connector.c
@@ -12,6 +12,7 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/regulator/consumer.h>
+#include <linux/workqueue.h>
 
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_bridge.h>
@@ -25,6 +26,8 @@ struct display_connector {
 
 	struct regulator	*supply;
 	struct gpio_desc	*ddc_en;
+
+	struct work_struct	hpd_work;
 };
 
 static inline struct display_connector *
@@ -92,15 +95,29 @@ static void display_connector_hpd_enable(struct drm_bridge *bridge)
 	struct display_connector *conn = to_display_connector(bridge);
 
 	enable_irq(conn->hpd_irq);
+
+	if (conn->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
+		schedule_work(&conn->hpd_work);
 }
 
 static void display_connector_hpd_disable(struct drm_bridge *bridge)
 {
 	struct display_connector *conn = to_display_connector(bridge);
 
+	if (conn->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
+		cancel_work_sync(&conn->hpd_work);
+
 	disable_irq(conn->hpd_irq);
 }
 
+static void display_connector_hpd_work(struct work_struct *work)
+{
+	struct display_connector *conn = container_of(work, struct display_connector, hpd_work);
+	struct drm_bridge *bridge = &conn->bridge;
+
+	drm_bridge_hpd_notify(bridge, display_connector_detect(bridge));
+}
+
 static const struct drm_edid *display_connector_edid_read(struct drm_bridge *bridge,
 							  struct drm_connector *connector)
 {
@@ -395,6 +412,8 @@ static int display_connector_probe(struct platform_device *pdev)
 		conn->bridge.ops |= DRM_BRIDGE_OP_DETECT;
 	if (conn->hpd_irq >= 0)
 		conn->bridge.ops |= DRM_BRIDGE_OP_HPD;
+	if (conn->hpd_irq >= 0 && type == DRM_MODE_CONNECTOR_DisplayPort)
+		INIT_WORK(&conn->hpd_work, display_connector_hpd_work);
 
 	dev_dbg(&pdev->dev,
 		"Found %s display connector '%s' %s DDC bus and %s HPD GPIO (ops 0x%x)\n",

-- 
2.47.3

Re: [PATCH 2/2] drm/bridge: display-connector: trigger initial HPD event for DP

Posted by Laurent Pinchart 2 weeks, 5 days ago

Hi Dmitry,

Thank you for the patch.

On Sat, Mar 14, 2026 at 02:43:12AM +0200, Dmitry Baryshkov wrote:
> If the DisplayPort drivers use display-connector for the HPD detection,
> the internal HPD state machine might be not active and thus the hardware
> might be not able to handle cable detection correctly. Instead it will
> depend on the externall HPD notifications to set the cable state,
> bypassing the internal HPD state machine (for example this is the case
> for the msm DP driver).
> 
> However if the cable has been plugged before the HPD IRQ has been
> enabled, there will be no HPD event coming. The drivers might fail
> detection in such a case. Trigger the HPD notification after enabling
> the HPD IRQ, propagating the cable insertion state.

The explanation makes sense, but it sounds like to could apply the same
way to HDMI. What am I missing ?

Also, wouldn't it be better if the DRM core interrogated the state of
the HPD signal when enabling HPD, instead of relying on all drivers to
implement something similar as this patch ?

> Fixes: 2e2bf3a5584d ("drm/bridge: display-connector: add DP support")
> Reported-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/bridge/display-connector.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/display-connector.c b/drivers/gpu/drm/bridge/display-connector.c
> index 6bb1134f75c3..f7a5bfd9c075 100644
> --- a/drivers/gpu/drm/bridge/display-connector.c
> +++ b/drivers/gpu/drm/bridge/display-connector.c
> @@ -12,6 +12,7 @@
>  #include <linux/of.h>
>  #include <linux/platform_device.h>
>  #include <linux/regulator/consumer.h>
> +#include <linux/workqueue.h>
>  
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_bridge.h>
> @@ -25,6 +26,8 @@ struct display_connector {
>  
>  	struct regulator	*supply;
>  	struct gpio_desc	*ddc_en;
> +
> +	struct work_struct	hpd_work;
>  };
>  
>  static inline struct display_connector *
> @@ -92,15 +95,29 @@ static void display_connector_hpd_enable(struct drm_bridge *bridge)
>  	struct display_connector *conn = to_display_connector(bridge);
>  
>  	enable_irq(conn->hpd_irq);
> +
> +	if (conn->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
> +		schedule_work(&conn->hpd_work);
>  }
>  
>  static void display_connector_hpd_disable(struct drm_bridge *bridge)
>  {
>  	struct display_connector *conn = to_display_connector(bridge);
>  
> +	if (conn->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
> +		cancel_work_sync(&conn->hpd_work);
> +
>  	disable_irq(conn->hpd_irq);
>  }
>  
> +static void display_connector_hpd_work(struct work_struct *work)
> +{
> +	struct display_connector *conn = container_of(work, struct display_connector, hpd_work);
> +	struct drm_bridge *bridge = &conn->bridge;
> +
> +	drm_bridge_hpd_notify(bridge, display_connector_detect(bridge));
> +}
> +
>  static const struct drm_edid *display_connector_edid_read(struct drm_bridge *bridge,
>  							  struct drm_connector *connector)
>  {
> @@ -395,6 +412,8 @@ static int display_connector_probe(struct platform_device *pdev)
>  		conn->bridge.ops |= DRM_BRIDGE_OP_DETECT;
>  	if (conn->hpd_irq >= 0)
>  		conn->bridge.ops |= DRM_BRIDGE_OP_HPD;
> +	if (conn->hpd_irq >= 0 && type == DRM_MODE_CONNECTOR_DisplayPort)
> +		INIT_WORK(&conn->hpd_work, display_connector_hpd_work);
>  
>  	dev_dbg(&pdev->dev,
>  		"Found %s display connector '%s' %s DDC bus and %s HPD GPIO (ops 0x%x)\n",
> 

-- 
Regards,

Laurent Pinchart

Re: [PATCH 2/2] drm/bridge: display-connector: trigger initial HPD event for DP

Posted by Dmitry Baryshkov 1 week, 6 days ago

Hi,

On Wed, 18 Mar 2026 at 19:40, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>

Sorry, I missed your email.

>
> On Sat, Mar 14, 2026 at 02:43:12AM +0200, Dmitry Baryshkov wrote:
> > If the DisplayPort drivers use display-connector for the HPD detection,
> > the internal HPD state machine might be not active and thus the hardware
> > might be not able to handle cable detection correctly. Instead it will
> > depend on the externall HPD notifications to set the cable state,
> > bypassing the internal HPD state machine (for example this is the case
> > for the msm DP driver).
> >
> > However if the cable has been plugged before the HPD IRQ has been
> > enabled, there will be no HPD event coming. The drivers might fail
> > detection in such a case. Trigger the HPD notification after enabling
> > the HPD IRQ, propagating the cable insertion state.
>
> The explanation makes sense, but it sounds like to could apply the same
> way to HDMI. What am I missing ?

Well... First of all, since HDMI doesn't have all DP magic, there is
no difference between HPD pin state and the display being plugged in
(so, e.g. dp-connector can't implement OP_DETECT, while hdmi-connector
does). For HDMI we usually don't have a complicated state machine in
the hardware. Nor do we have a an AUX bus with timeouts, etc.

>
> Also, wouldn't it be better if the DRM core interrogated the state of
> the HPD signal when enabling HPD, instead of relying on all drivers to
> implement something similar as this patch ?

Most of the drivers don't require this. It is only limited to the
OP_HPD bridges which don't implement OP_DETECT.

>
> > Fixes: 2e2bf3a5584d ("drm/bridge: display-connector: add DP support")
> > Reported-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> > ---
> >  drivers/gpu/drm/bridge/display-connector.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)



--
With best wishes
Dmitry

[PATCH 1/2] drm/bridge: display-connector: don't autoenable HPD IRQ
[PATCH 2/2] drm/bridge: display-connector: trigger initial HPD event for DP