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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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