4 files changed, 68 insertions, 37 deletions
diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 2ea6ffc9b22bae..96c453980ab6e1 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -475,25 +475,22 @@ Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp
 As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in
 drm_panel"), we have a check in the drm_panel core to make sure nobody
 double-calls prepare/enable/disable/unprepare. Eventually that should probably
-be turned into a WARN_ON() or somehow made louder, but right now we actually
-expect it to trigger and so we don't want it to be too loud.
-
-Specifically, that warning will trigger for panel-edp and panel-simple at
-shutdown time because those panels hardcode a call to drm_panel_disable()
-and drm_panel_unprepare() at shutdown and remove time that they call regardless
-of panel state. On systems with a properly coded DRM modeset driver that
-calls drm_atomic_helper_shutdown() this is pretty much guaranteed to cause
-the warning to fire.
-
-Unfortunately we can't safely remove the calls in panel-edp and panel-simple
-until we're sure that all DRM modeset drivers that are used with those panels
-properly call drm_atomic_helper_shutdown(). This TODO item is to validate
-that all DRM modeset drivers used with panel-edp and panel-simple properly
-call drm_atomic_helper_shutdown() and then remove the calls to
-disable/unprepare from those panels. Alternatively, this TODO item could be
-removed by convincing stakeholders that those calls are fine and downgrading
-the error message in drm_panel_disable() / drm_panel_unprepare() to a
-debug-level message.
+be turned into a WARN_ON() or somehow made louder.
+
+At the moment, we expect that we may still encounter the warnings in the
+drm_panel core when using panel-simple and panel-edp. Since those panel
+drivers are used with a lot of different DRM modeset drivers they still
+make an extra effort to disable/unprepare the panel themsevles at shutdown
+time. Specifically we could still encounter those warnings if the panel
+driver gets shutdown() _before_ the DRM modeset driver and the DRM modeset
+driver properly calls drm_atomic_helper_shutdown() in its own shutdown()
+callback. Warnings could be avoided in such a case by using something like
+device links to ensure that the panel gets shutdown() after the DRM modeset
+driver.
+
+Once all DRM modeset drivers are known to shutdown properly, the extra
+calls to disable/unprepare in remove/shutdown in panel-simple and panel-edp
+should be removed and this TODO item marked complete.
 
 Contact: Douglas Anderson <dianders@chromium.org>
 
diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index cfbe020de54e01..19ab0a794add31 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -161,6 +161,15 @@ int drm_panel_unprepare(struct drm_panel *panel)
 	if (!panel)
 		return -EINVAL;
 
+	/*
+	 * If you are seeing the warning below it likely means one of two things:
+	 * - Your panel driver incorrectly calls drm_panel_unprepare() in its
+	 *   shutdown routine. You should delete this.
+	 * - You are using panel-edp or panel-simple and your DRM modeset
+	 *   driver's shutdown() callback happened after the panel's shutdown().
+	 *   In this case the warning is harmless though ideally you should
+	 *   figure out how to reverse the order of the shutdown() callbacks.
+	 */
 	if (!panel->prepared) {
 		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
 		return 0;
@@ -245,6 +254,15 @@ int drm_panel_disable(struct drm_panel *panel)
 	if (!panel)
 		return -EINVAL;
 
+	/*
+	 * If you are seeing the warning below it likely means one of two things:
+	 * - Your panel driver incorrectly calls drm_panel_disable() in its
+	 *   shutdown routine. You should delete this.
+	 * - You are using panel-edp or panel-simple and your DRM modeset
+	 *   driver's shutdown() callback happened after the panel's shutdown().
+	 *   In this case the warning is harmless though ideally you should
+	 *   figure out how to reverse the order of the shutdown() callbacks.
+	 */
 	if (!panel->enabled) {
 		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
 		return 0;
diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
index 6b16e263d137ea..e17e0d9e7ebb03 100644
--- a/drivers/gpu/drm/panel/panel-edp.c
+++ b/drivers/gpu/drm/panel/panel-edp.c
@@ -954,16 +954,24 @@ static void panel_edp_shutdown(struct device *dev)
 	 * drm_atomic_helper_shutdown() at shutdown time and that should
 	 * cause the panel to be disabled / unprepared if needed. For now,
 	 * however, we'll keep these calls due to the sheer number of
-	 * different DRM modeset drivers used with panel-edp. The fact that
-	 * we're calling these and _also_ the drm_atomic_helper_shutdown()
-	 * will try to disable/unprepare means that we can get a warning about
-	 * trying to disable/unprepare an already disabled/unprepared panel,
-	 * but that's something we'll have to live with until we've confirmed
-	 * that all DRM modeset drivers are properly calling
-	 * drm_atomic_helper_shutdown().
+	 * different DRM modeset drivers used with panel-edp. Once we've
+	 * confirmed that all DRM modeset drivers using this panel properly
+	 * call drm_atomic_helper_shutdown() we can simply delete the two
+	 * calls below.
+	 *
+	 * TO BE EXPLICIT: THE CALLS BELOW SHOULDN'T BE COPIED TO ANY NEW
+	 * PANEL DRIVERS.
+	 *
+	 * FIXME: If we're still haven't figured out if all DRM modeset
+	 * drivers properly call drm_atomic_helper_shutdown() but we _have_
+	 * managed to make sure that DRM modeset drivers get their shutdown()
+	 * callback before the panel's shutdown() callback (perhaps using
+	 * device link), we could add a WARN_ON here to help move forward.
 	 */
-	drm_panel_disable(&panel->base);
-	drm_panel_unprepare(&panel->base);
+	if (panel->base.enabled)
+		drm_panel_disable(&panel->base);
+	if (panel->base.prepared)
+		drm_panel_unprepare(&panel->base);
 }
 
 static void panel_edp_remove(struct device *dev)
diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 4a3264130ddc05..7ad5996b563b75 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -726,16 +726,24 @@ static void panel_simple_shutdown(struct device *dev)
 	 * drm_atomic_helper_shutdown() at shutdown time and that should
 	 * cause the panel to be disabled / unprepared if needed. For now,
 	 * however, we'll keep these calls due to the sheer number of
-	 * different DRM modeset drivers used with panel-simple. The fact that
-	 * we're calling these and _also_ the drm_atomic_helper_shutdown()
-	 * will try to disable/unprepare means that we can get a warning about
-	 * trying to disable/unprepare an already disabled/unprepared panel,
-	 * but that's something we'll have to live with until we've confirmed
-	 * that all DRM modeset drivers are properly calling
-	 * drm_atomic_helper_shutdown().
+	 * different DRM modeset drivers used with panel-simple. Once we've
+	 * confirmed that all DRM modeset drivers using this panel properly
+	 * call drm_atomic_helper_shutdown() we can simply delete the two
+	 * calls below.
+	 *
+	 * TO BE EXPLICIT: THE CALLS BELOW SHOULDN'T BE COPIED TO ANY NEW
+	 * PANEL DRIVERS.
+	 *
+	 * FIXME: If we're still haven't figured out if all DRM modeset
+	 * drivers properly call drm_atomic_helper_shutdown() but we _have_
+	 * managed to make sure that DRM modeset drivers get their shutdown()
+	 * callback before the panel's shutdown() callback (perhaps using
+	 * device link), we could add a WARN_ON here to help move forward.
 	 */
-	drm_panel_disable(&panel->base);
-	drm_panel_unprepare(&panel->base);
+	if (panel->base.enabled)
+		drm_panel_disable(&panel->base);
+	if (panel->base.prepared)
+		drm_panel_unprepare(&panel->base);
 }
 
 static void panel_simple_remove(struct device *dev)