drm/panel: make prepare/enable and disable/unprepare calls return void

Now there are no users of the return value of the drm_panel_prepare(),
drm_panel_unprepare(), drm_panel_enable() and drm_panel_disable() calls.
Usually these calls are performed from the atomic callbacks, where it is
impossible to return an error. Stop returning error codes and return
void instead.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250401-panel-return-void-v1-7-93e1be33dc8d@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

drivers/gpu/drm/drm_panel.c

@@ -106,21 +106,21 @@ EXPORT_SYMBOL(drm_panel_remove);
  *
  * Calling this function will enable power and deassert any reset signals to
  * the panel. After this has completed it is possible to communicate with any
- * integrated circuitry via a command bus.
- *
- * Return: 0 on success or a negative error code on failure.
+ * integrated circuitry via a command bus. This function cannot fail (as it is
+ * called from the pre_enable call chain). There will always be a call to
+ * drm_panel_disable() afterwards.
  */
-int drm_panel_prepare(struct drm_panel *panel)
+void drm_panel_prepare(struct drm_panel *panel)
 {
 	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
-		return -EINVAL;
+		return;
 
 	if (panel->prepared) {
 		dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
-		return 0;
+		return;
 	}
 
 	mutex_lock(&panel->follower_lock);
@@ -139,11 +139,8 @@ int drm_panel_prepare(struct drm_panel *panel)
 				 follower->funcs->panel_prepared, ret);
 	}
 
-	ret = 0;
 exit:
 	mutex_unlock(&panel->follower_lock);
-
-	return ret;
 }
 EXPORT_SYMBOL(drm_panel_prepare);
 
@@ -155,16 +152,14 @@ EXPORT_SYMBOL(drm_panel_prepare);
  * reset, turn off power supplies, ...). After this function has completed, it
  * is usually no longer possible to communicate with the panel until another
  * call to drm_panel_prepare().
- *
- * Return: 0 on success or a negative error code on failure.
  */
-int drm_panel_unprepare(struct drm_panel *panel)
+void drm_panel_unprepare(struct drm_panel *panel)
 {
 	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
-		return -EINVAL;
+		return;
 
 	/*
 	 * If you are seeing the warning below it likely means one of two things:
@@ -177,7 +172,7 @@ int drm_panel_unprepare(struct drm_panel *panel)
 	 */
 	if (!panel->prepared) {
 		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
-		return 0;
+		return;
 	}
 
 	mutex_lock(&panel->follower_lock);
@@ -196,11 +191,8 @@ int drm_panel_unprepare(struct drm_panel *panel)
 	}
 	panel->prepared = false;
 
-	ret = 0;
 exit:
 	mutex_unlock(&panel->follower_lock);
-
-	return ret;
 }
 EXPORT_SYMBOL(drm_panel_unprepare);
 
@@ -210,26 +202,26 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  *
  * Calling this function will cause the panel display drivers to be turned on
  * and the backlight to be enabled. Content will be visible on screen after
- * this call completes.
- *
- * Return: 0 on success or a negative error code on failure.
+ * this call completes. This function cannot fail (as it is called from the
+ * enable call chain). There will always be a call to drm_panel_disable()
+ * afterwards.
  */
-int drm_panel_enable(struct drm_panel *panel)
+void drm_panel_enable(struct drm_panel *panel)
 {
 	int ret;
 
 	if (!panel)
-		return -EINVAL;
+		return;
 
 	if (panel->enabled) {
 		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
-		return 0;
+		return;
 	}
 
 	if (panel->funcs && panel->funcs->enable) {
 		ret = panel->funcs->enable(panel);
 		if (ret < 0)
-			return ret;
+			return;
 	}
 	panel->enabled = true;
 
@@ -237,8 +229,6 @@ int drm_panel_enable(struct drm_panel *panel)
 	if (ret < 0)
 		DRM_DEV_INFO(panel->dev, "failed to enable backlight: %d\n",
 			     ret);
-
-	return 0;
 }
 EXPORT_SYMBOL(drm_panel_enable);
 
@@ -249,15 +239,13 @@ EXPORT_SYMBOL(drm_panel_enable);
  * This will typically turn off the panel's backlight or disable the display
  * drivers. For smart panels it should still be possible to communicate with
  * the integrated circuitry via any command bus after this call.
- *
- * Return: 0 on success or a negative error code on failure.
  */
-int drm_panel_disable(struct drm_panel *panel)
+void drm_panel_disable(struct drm_panel *panel)
 {
 	int ret;
 
 	if (!panel)
-		return -EINVAL;
+		return;
 
 	/*
 	 * If you are seeing the warning below it likely means one of two things:
@@ -270,7 +258,7 @@ int drm_panel_disable(struct drm_panel *panel)
 	 */
 	if (!panel->enabled) {
 		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
-		return 0;
+		return;
 	}
 
 	ret = backlight_disable(panel->backlight);
@@ -281,11 +269,9 @@ int drm_panel_disable(struct drm_panel *panel)
 	if (panel->funcs && panel->funcs->disable) {
 		ret = panel->funcs->disable(panel);
 		if (ret < 0)
-			return ret;
+			return;
 	}
 	panel->enabled = false;
-
-	return 0;
 }
 EXPORT_SYMBOL(drm_panel_disable);
 

drivers/gpu/drm/panel/panel-newvision-nv3051d.c

@@ -413,15 +413,10 @@ static int panel_nv3051d_probe(struct mipi_dsi_device *dsi)
 static void panel_nv3051d_shutdown(struct mipi_dsi_device *dsi)
 {
 	struct panel_nv3051d *ctx = mipi_dsi_get_drvdata(dsi);
-	int ret;
 
-	ret = drm_panel_unprepare(&ctx->panel);
-	if (ret < 0)
-		dev_err(&dsi->dev, "Failed to unprepare panel: %d\n", ret);
+	drm_panel_unprepare(&ctx->panel);
 
-	ret = drm_panel_disable(&ctx->panel);
-	if (ret < 0)
-		dev_err(&dsi->dev, "Failed to disable panel: %d\n", ret);
+	drm_panel_disable(&ctx->panel);
 }
 
 static void panel_nv3051d_remove(struct mipi_dsi_device *dsi)

include/drm/drm_panel.h

@@ -316,11 +316,11 @@ void drm_panel_put(struct drm_panel *panel);
 void drm_panel_add(struct drm_panel *panel);
 void drm_panel_remove(struct drm_panel *panel);
 
-int drm_panel_prepare(struct drm_panel *panel);
-int drm_panel_unprepare(struct drm_panel *panel);
+void drm_panel_prepare(struct drm_panel *panel);
+void drm_panel_unprepare(struct drm_panel *panel);
 
-int drm_panel_enable(struct drm_panel *panel);
-int drm_panel_disable(struct drm_panel *panel);
+void drm_panel_enable(struct drm_panel *panel);
+void drm_panel_disable(struct drm_panel *panel);
 
 int drm_panel_get_modes(struct drm_panel *panel, struct drm_connector *connector);