drm: Introduce epoch counter to drm_connector

This counter will be used by drm_helper_probe_detect caller to determine
if anything had changed(including edid, connection status and etc).
Hardware specific driver detect hooks are responsible for updating this
counter when some change is detected to notify the drm part,
which can trigger for example hotplug event.

Also now call drm_connector_update_edid_property
right after we get edid always to make sure there is a
unified way to handle edid change, without having to
change tons of source code as currently
drm_connector_update_edid_property is called only in
certain cases like reprobing and not right after edid is
actually updated.

v2: Added documentation for the new counter. Rename change_counter to
    epoch_counter.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105540

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200630002700.5451-3-kunal1.joshi@intel.com

drivers/gpu/drm/drm_probe_helper.c

@@ -292,6 +292,9 @@ retry:
 	if (WARN_ON(ret < 0))
 		ret = connector_status_unknown;
 
+	if (ret != connector->status)
+		connector->epoch_counter += 1;
+
 	drm_modeset_drop_locks(&ctx);
 	drm_modeset_acquire_fini(&ctx);
 
@@ -325,11 +328,16 @@ drm_helper_probe_detect(struct drm_connector *connector,
 		return ret;
 
 	if (funcs->detect_ctx)
-		return funcs->detect_ctx(connector, ctx, force);
+		ret = funcs->detect_ctx(connector, ctx, force);
 	else if (connector->funcs->detect)
-		return connector->funcs->detect(connector, force);
+		ret = connector->funcs->detect(connector, force);
 	else
-		return connector_status_connected;
+		ret = connector_status_connected;
+
+	if (ret != connector->status)
+		connector->epoch_counter += 1;
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_helper_probe_detect);
 
@@ -779,6 +787,7 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 	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;
@@ -792,20 +801,39 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 
 		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));
-		if (old_status != 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;
+
 	}
 	drm_connector_list_iter_end(&conn_iter);
 	mutex_unlock(&dev->mode_config.mutex);
 
-	if (changed)
+	if (changed) {
 		drm_kms_helper_hotplug_event(dev);
+		DRM_DEBUG_KMS("Sent hotplug event\n");
+	}
 
 	return changed;
 }