linux-kernel - [PATCH 1/2] drm/panel: Allow powering on panel follower after panel is enabled

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Message-ID: <20250731101344.2761757-1-treapking@google.com>
Date: Thu, 31 Jul 2025 18:13:14 +0800
From: Pin-Yen Lin <treapking@...omium.org>
To: Neil Armstrong <neil.armstrong@...aro.org>,
	Jessica Zhang <quic_jesszhan@...cinc.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Jiri Kosina <jikos@...nel.org>,
	Benjamin Tissoires <bentiss@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org,
	Douglas Anderson <dianders@...omium.org>,
	dri-devel@...ts.freedesktop.org,
	Chen-Yu Tsai <wenst@...omium.org>,
	Pin-Yen Lin <treapking@...gle.com>
Subject: [PATCH 1/2] 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 after_panel_enabled
flag to the panel follower and power on the device after the panel and
its backlight are enabled.

Signed-off-by: Pin-Yen Lin <treapking@...gle.com>
---

 drivers/gpu/drm/drm_panel.c | 47 +++++++++++++++++++++++++++++++++----
 include/drm/drm_panel.h     |  8 +++++++
 2 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 650de4da08537..58125f8418f37 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -133,6 +133,9 @@ void drm_panel_prepare(struct drm_panel *panel)
 	panel->prepared = true;
 
 	list_for_each_entry(follower, &panel->followers, list) {
+		if (follower->after_panel_enabled)
+			continue;
+
 		ret = follower->funcs->panel_prepared(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
@@ -178,6 +181,9 @@ void drm_panel_unprepare(struct drm_panel *panel)
 	mutex_lock(&panel->follower_lock);
 
 	list_for_each_entry(follower, &panel->followers, list) {
+		if (follower->after_panel_enabled)
+			continue;
+
 		ret = follower->funcs->panel_unpreparing(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
@@ -208,6 +214,7 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  */
 void drm_panel_enable(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -218,10 +225,12 @@ 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;
 
@@ -229,6 +238,18 @@ void drm_panel_enable(struct drm_panel *panel)
 	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->after_panel_enabled)
+			continue;
+
+		ret = follower->funcs->panel_prepared(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_prepared, ret);
+	}
+exit:
+	mutex_unlock(&panel->follower_lock);
 }
 EXPORT_SYMBOL(drm_panel_enable);
 
@@ -242,6 +263,7 @@ EXPORT_SYMBOL(drm_panel_enable);
  */
 void drm_panel_disable(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -261,6 +283,18 @@ void drm_panel_disable(struct drm_panel *panel)
 		return;
 	}
 
+	mutex_lock(&panel->follower_lock);
+
+	list_for_each_entry(follower, &panel->followers, list) {
+		if (!follower->after_panel_enabled)
+			continue;
+
+		ret = follower->funcs->panel_unpreparing(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_unpreparing, ret);
+	}
+
 	ret = backlight_disable(panel->backlight);
 	if (ret < 0)
 		DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
@@ -269,9 +303,12 @@ 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);
 
@@ -537,7 +574,8 @@ 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->after_panel_enabled) ||
+	    (panel->enabled && follower->after_panel_enabled)) {
 		ret = follower->funcs->panel_prepared(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
@@ -566,7 +604,8 @@ void drm_panel_remove_follower(struct drm_panel_follower *follower)
 
 	mutex_lock(&panel->follower_lock);
 
-	if (panel->prepared) {
+	if ((panel->prepared && !follower->after_panel_enabled) ||
+	    (panel->enabled && follower->after_panel_enabled)) {
 		ret = follower->funcs->panel_unpreparing(follower);
 		if (ret < 0)
 			dev_info(panel->dev, "%ps failed: %d\n",
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 843fb756a2950..aa9b6218702fd 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -183,6 +183,14 @@ struct drm_panel_follower {
 	 * The panel we're dependent on; set by drm_panel_add_follower().
 	 */
 	struct drm_panel *panel;
+
+	/**
+	 * @after_panel_enabled
+	 *
+	 * If true then this panel follower should be powered after the panel
+	 * and the backlight are enabled, instead of after panel is prepared.
+	 */
+	bool after_panel_enabled;
 };
 
 /**
-- 
2.50.1.552.g942d659e1b-goog