The drm_helper_hpd_irq_event() documentation states that this function is "useful for drivers which can't or don't track hotplug interrupts for each connector." and that "Drivers which support hotplug interrupts for each connector individually and which have a more fine-grained detect logic should bypass this code and directly call drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.

However, what this actually means, and is further explained in the drm_kms_helper_hotplug_event() documentation, is that drm_kms_helper_hotplug_event() should be called by drivers that can track the connection status change, and if it has changed we should call that function.

This underlying expectation we failed to provide is that the caller of drm_kms_helper_hotplug_event() should call drm_helper_probe_detect() to probe the new status of the connector.

Since we didn't do it, it meant that even though we were sending the notification to user-space and the DRM clients that something changed we never probed or updated our internal connector status ourselves.

This went mostly unnoticed since the detect callback usually doesn't have any side-effect. Also, if we were using the DRM fbdev emulation (which is a DRM client), or any user-space application that can deal with hotplug events, chances are they would react to the hotplug event by probing the connector status eventually.

However, now that we have to enable the scrambler in detect() if it was enabled it has a side effect, and an application such as Kodi or modetest doesn't deal with hotplug events. This resulted with a black screen when Kodi or modetest was running when a screen was disconnected and then reconnected, or switched off and on.

Signed-off-by: Maxime Ripard maxime@cerno.tech --- drivers/gpu/drm/vc4/vc4_hdmi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c index a3dbd1fdff7d..d9e001b9314f 100644 --- a/drivers/gpu/drm/vc4/vc4_hdmi.c +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c @@ -1578,10 +1578,11 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *vc4_hdmi) static irqreturn_t vc4_hdmi_hpd_irq_thread(int irq, void *priv) { struct vc4_hdmi *vc4_hdmi = priv; - struct drm_device *dev = vc4_hdmi->connector.dev; + struct drm_connector *connector = &vc4_hdmi->connector; + struct drm_device *dev = connector->dev;

if (dev && dev->registered) - drm_kms_helper_hotplug_event(dev); + drm_connector_helper_hpd_irq_event(connector);

return IRQ_HANDLED; }

On Thu, Aug 19, 2021 at 03:44:53PM +0200, Maxime Ripard wrote:

The drm_helper_hpd_irq_event() function is iterating over all the connectors when an hotplug event is detected.

During that iteration, it will call each connector detect function and figure out if its status changed.

Finally, if any connector changed, it will notify the user-space and the clients that something changed on the DRM device.

This is supposed to be used for drivers that don't have a hotplug interrupt for individual connectors. However, drivers that can use an interrupt for a single connector are left in the dust and can either reimplement the logic used during the iteration for each connector or use that helper and iterate over all connectors all the time.

Since both are suboptimal, let's create a helper that will only perform the status detection on a single connector.

Signed-off-by: Maxime Ripard maxime@cerno.tech

drivers/gpu/drm/drm_probe_helper.c | 105 ++++++++++++++++++++--------- include/drm/drm_probe_helper.h | 1 + 2 files changed, 74 insertions(+), 32 deletions(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 5606bca3caa8..7e3cbb4333ce 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -795,6 +795,77 @@ void drm_kms_helper_poll_fini(struct drm_device *dev) } EXPORT_SYMBOL(drm_kms_helper_poll_fini);

+static bool +_drm_connector_helper_hpd_irq_event(struct drm_connector *connector,

• 		    bool notify)
  

+{

• struct drm_device *dev = connector->dev;
• enum drm_connector_status old_status;
• u64 old_epoch_counter;
• bool changed = false;
• /* Only handle HPD capable connectors. */
• drm_WARN_ON(dev, !(connector->polled & DRM_CONNECTOR_POLL_HPD));
• drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
• old_status = connector->status;
• old_epoch_counter = connector->epoch_counter;
• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Old epoch counter %llu\n",

•       connector->base.id,
  

•       connector->name,
  

•       old_epoch_counter);
  

• connector->status = drm_helper_probe_detect(connector, NULL,

• 				    false);
  

• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",

•       connector->base.id,
  

•       connector->name,
  

•       drm_get_connector_status_name(old_status),
  

•       drm_get_connector_status_name(connector->status));
  

• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] New epoch counter %llu\n",

•       connector->base.id,
  

•       connector->name,
  

•       connector->epoch_counter);
  

• /*

• * Check if epoch counter had changed, meaning that we need
  

• * to send a uevent.
  

• */
  

• if (old_epoch_counter != connector->epoch_counter)

• changed = true;
  

• if (changed && notify) {

• drm_kms_helper_hotplug_event(dev);
  

• DRM_DEBUG_KMS("Sent hotplug event\n");
  

• }
• return changed;

+}

+/**

• • drm_connector_helper_hpd_irq_event - hotplug processing
• • @connector: drm_connector
• • Drivers can use this helper function to run a detect cycle on a connector
• • which has the DRM_CONNECTOR_POLL_HPD flag set in its &polled member.
• • This helper function is useful for drivers which can track hotplug
• • interrupts for a single connector.
• • This function must be called with the mode setting locks held.
• • Note that a connector can be both polled and probed from the hotplug
• • handler, in case the hotplug interrupt is known to be unreliable.
• */

Adding a sentence here to point to the other helper for global hpd irq and vice versa would be neat. -Daniel

+bool drm_connector_helper_hpd_irq_event(struct drm_connector *connector) +{

• return _drm_connector_helper_hpd_irq_event(connector, true);

+} +EXPORT_SYMBOL(drm_connector_helper_hpd_irq_event);

/**

• drm_helper_hpd_irq_event - hotplug processing
• @dev: drm_device

@@ -822,9 +893,7 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev) { struct drm_connector *connector; struct drm_connector_list_iter conn_iter;

• enum drm_connector_status old_status; bool changed = false;

• u64 old_epoch_counter;

  if (!dev->mode_config.poll_enabled) return false;

@@ -832,37 +901,9 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev) mutex_lock(&dev->mode_config.mutex); drm_connector_list_iter_begin(dev, &conn_iter); drm_for_each_connector_iter(connector, &conn_iter) {

• /* Only handle HPD capable connectors. */
  

• if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
  

• 	continue;
  

• old_status = connector->status;
  

• old_epoch_counter = connector->epoch_counter;
  

• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Old epoch counter %llu\n", connector->base.id,
  

• 	      connector->name,
  

• 	      old_epoch_counter);
  

• connector->status = drm_helper_probe_detect(connector, NULL, false);
  

• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
  

• 	      connector->base.id,
  

• 	      connector->name,
  

• 	      drm_get_connector_status_name(old_status),
  

• 	      drm_get_connector_status_name(connector->status));
  

• DRM_DEBUG_KMS("[CONNECTOR:%d:%s] New epoch counter %llu\n",
  

• 	      connector->base.id,
  

• 	      connector->name,
  

• 	      connector->epoch_counter);
  

• /*
  

•  * Check if epoch counter had changed, meaning that we need
  

•  * to send a uevent.
  

•  */
  

• if (old_epoch_counter != connector->epoch_counter)
  

• if (_drm_connector_helper_hpd_irq_event(connector,
  

• 					false))
  changed = true;
  

• } drm_connector_list_iter_end(&conn_iter); mutex_unlock(&dev->mode_config.mutex);

diff --git a/include/drm/drm_probe_helper.h b/include/drm/drm_probe_helper.h index 8d3ed2834d34..04c57564c397 100644 --- a/include/drm/drm_probe_helper.h +++ b/include/drm/drm_probe_helper.h @@ -18,6 +18,7 @@ int drm_helper_probe_detect(struct drm_connector *connector, void drm_kms_helper_poll_init(struct drm_device *dev); void drm_kms_helper_poll_fini(struct drm_device *dev); bool drm_helper_hpd_irq_event(struct drm_device *dev); +bool drm_connector_helper_hpd_irq_event(struct drm_connector *connector); void drm_kms_helper_hotplug_event(struct drm_device *dev);

void drm_kms_helper_poll_disable(struct drm_device *dev);

2.31.1