drm/panel: Allow powering on panel follower after panel is enabled

Some touch controllers have to be powered on after the panel's backlight
is enabled. To support these controllers, introduce .panel_enabled() and
.panel_disabling() to panel_follower_funcs and use them to power on the
device after the panel and its backlight are enabled.

Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20250818115015.2909525-1-treapking@chromium.org

Author: ppetter1025

drivers/gpu/drm/drm_panel.c

@@ -134,6 +134,9 @@ void drm_panel_prepare(struct drm_panel *panel)
 	panel->prepared = true;
 
 	list_for_each_entry(follower, &panel->followers, list) {
+		if (!follower->funcs->panel_prepared)
+			continue;
+
 		ret = follower->funcs->panel_prepared(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
@@ -179,6 +182,9 @@ void drm_panel_unprepare(struct drm_panel *panel)
 	mutex_lock(&panel->follower_lock);
 
 	list_for_each_entry(follower, &panel->followers, list) {
+		if (!follower->funcs->panel_unpreparing)
+			continue;
+
 		ret = follower->funcs->panel_unpreparing(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
@@ -209,6 +215,7 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  */
 void drm_panel_enable(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -219,17 +226,32 @@ void drm_panel_enable(struct drm_panel *panel)
 		return;
 	}
 
+	mutex_lock(&panel->follower_lock);
+
 	if (panel->funcs && panel->funcs->enable) {
 		ret = panel->funcs->enable(panel);
 		if (ret < 0)
-			return;
+			goto exit;
 	}
 	panel->enabled = true;
 
 	ret = backlight_enable(panel->backlight);
 	if (ret < 0)
 		DRM_DEV_INFO(panel->dev, "failed to enable backlight: %d\n",
 			     ret);
+
+	list_for_each_entry(follower, &panel->followers, list) {
+		if (!follower->funcs->panel_enabled)
+			continue;
+
+		ret = follower->funcs->panel_enabled(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_enabled, ret);
+	}
+
+exit:
+	mutex_unlock(&panel->follower_lock);
 }
 EXPORT_SYMBOL(drm_panel_enable);
 
@@ -243,6 +265,7 @@ EXPORT_SYMBOL(drm_panel_enable);
  */
 void drm_panel_disable(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -262,6 +285,18 @@ void drm_panel_disable(struct drm_panel *panel)
 		return;
 	}
 
+	mutex_lock(&panel->follower_lock);
+
+	list_for_each_entry(follower, &panel->followers, list) {
+		if (!follower->funcs->panel_disabling)
+			continue;
+
+		ret = follower->funcs->panel_disabling(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_disabling, ret);
+	}
+
 	ret = backlight_disable(panel->backlight);
 	if (ret < 0)
 		DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
@@ -270,9 +305,12 @@ void drm_panel_disable(struct drm_panel *panel)
 	if (panel->funcs && panel->funcs->disable) {
 		ret = panel->funcs->disable(panel);
 		if (ret < 0)
-			return;
+			goto exit;
 	}
 	panel->enabled = false;
+
+exit:
+	mutex_unlock(&panel->follower_lock);
 }
 EXPORT_SYMBOL(drm_panel_disable);
 
@@ -539,13 +577,13 @@ EXPORT_SYMBOL(drm_is_panel_follower);
  * @follower_dev: The 'struct device' for the follower.
  * @follower:     The panel follower descriptor for the follower.
  *
- * A panel follower is called right after preparing the panel and right before
- * unpreparing the panel. It's primary intention is to power on an associated
- * touchscreen, though it could be used for any similar devices. Multiple
- * devices are allowed the follow the same panel.
+ * A panel follower is called right after preparing/enabling the panel and right
+ * before unpreparing/disabling the panel. It's primary intention is to power on
+ * an associated touchscreen, though it could be used for any similar devices.
+ * Multiple devices are allowed the follow the same panel.
  *
- * If a follower is added to a panel that's already been turned on, the
- * follower's prepare callback is called right away.
+ * If a follower is added to a panel that's already been prepared/enabled, the
+ * follower's prepared/enabled callback is called right away.
  *
  * The "panel" property of the follower points to the panel to be followed.
  *
@@ -569,12 +607,18 @@ int drm_panel_add_follower(struct device *follower_dev,
 	mutex_lock(&panel->follower_lock);
 
 	list_add_tail(&follower->list, &panel->followers);
-	if (panel->prepared) {
+	if (panel->prepared && follower->funcs->panel_prepared) {
 		ret = follower->funcs->panel_prepared(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
 				 follower->funcs->panel_prepared, ret);
 	}
+	if (panel->enabled && follower->funcs->panel_enabled) {
+		ret = follower->funcs->panel_enabled(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_enabled, ret);
+	}
 
 	mutex_unlock(&panel->follower_lock);
 
@@ -587,7 +631,8 @@ EXPORT_SYMBOL(drm_panel_add_follower);
  * @follower:     The panel follower descriptor for the follower.
  *
  * Undo drm_panel_add_follower(). This includes calling the follower's
- * unprepare function if we're removed from a panel that's currently prepared.
+ * unpreparing/disabling function if we're removed from a panel that's currently
+ * prepared/enabled.
  *
  * Return: 0 or an error code.
  */
@@ -598,7 +643,13 @@ void drm_panel_remove_follower(struct drm_panel_follower *follower)
 
 	mutex_lock(&panel->follower_lock);
 
-	if (panel->prepared) {
+	if (panel->enabled && follower->funcs->panel_disabling) {
+		ret = follower->funcs->panel_disabling(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_disabling, ret);
+	}
+	if (panel->prepared && follower->funcs->panel_unpreparing) {
 		ret = follower->funcs->panel_unpreparing(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",

include/drm/drm_panel.h

@@ -160,6 +160,20 @@ struct drm_panel_follower_funcs {
 	 * Called before the panel is powered off.
 	 */
 	int (*panel_unpreparing)(struct drm_panel_follower *follower);
+
+	/**
+	 * @panel_enabled:
+	 *
+	 * Called after the panel and the backlight have been enabled.
+	 */
+	int (*panel_enabled)(struct drm_panel_follower *follower);
+
+	/**
+	 * @panel_disabling:
+	 *
+	 * Called before the panel and the backlight are disabled.
+	 */
+	int (*panel_disabling)(struct drm_panel_follower *follower);
 };
 
 struct drm_panel_follower {