[PATCH v3 03/12] drm/panel: Keep track of enabled/prepared

[Sean Paul]

This patch adds state tracking to the drm_panel functions which keep
track of enabled and prepared. If the calls are unbalanced, a WARNING is
issued.

The motivation for this change is that a number of panel drivers
(including panel-simple) all do this to protect their regulator
refcounts. The atomic framework ensures the calls are balanced, and
there  aren't any panel drivers being used by legacy drivers. As such,
these checks are useless, but let's add a WARNING just in case something
crazy happens (like a legacy driver using a panel).

Less code == better.

Changes in v2:
 - Reduced enabled/prepared bools to one enum (Andrzej)
 - Don't update state if the operation fails (Andrzej)
 - Issue warning even if operation is not implemented

Changes in v3:
 - Functions no longer static inline (Daniel)
 - Added a helper function to share state change code (Andrzej)
 - Only warn when a panel is present (Daniel)
 - Update state if function is not implemented (Andrzej)

Cc: Andrzej Hajda <a.hajda at samsung.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Sean Paul <seanpaul at chromium.org>
---
 drivers/gpu/drm/drm_panel.c | 63 ++++++++++++++++++++++++++++++++++++---------
 include/drm/drm_panel.h     | 15 +++++++++++
 2 files changed, 66 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 6f28598a5d0e..6547850b5e80 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -21,6 +21,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/bug.h>
 #include <linux/err.h>
 #include <linux/module.h>
 
@@ -48,6 +49,7 @@ static LIST_HEAD(panel_list);
 void drm_panel_init(struct drm_panel *panel)
 {
 	INIT_LIST_HEAD(&panel->list);
+	panel->state = DRM_PANEL_POWER_OFF;
 }
 EXPORT_SYMBOL(drm_panel_init);
 
@@ -126,6 +128,23 @@ int drm_panel_detach(struct drm_panel *panel)
 }
 EXPORT_SYMBOL(drm_panel_detach);
 
+static int drm_panel_change_state(struct drm_panel *panel,
+				  enum drm_panel_state cur_state,
+				  enum drm_panel_state new_state,
+				  int (*hook)(struct drm_panel *panel))
+{
+	int ret;
+
+	WARN_ON(panel->state != cur_state);
+	if (hook)
+		ret = hook(panel);
+	else
+		ret = -ENOSYS;
+
+	panel->state = new_state;
+	return ret;
+}
+
 /**
  * drm_panel_unprepare - power off a panel
  * @panel: DRM panel
@@ -135,14 +154,19 @@ EXPORT_SYMBOL(drm_panel_detach);
  * is usually no longer possible to communicate with the panel until another
  * call to drm_panel_prepare().
  *
+ * Atomic framework will ensure that prepare/unprepare are properly balanced.
+ * If this is not the case, a WARNING will be issued.
+ *
  * Return: 0 on success or a negative error code on failure.
  */
 int drm_panel_unprepare(struct drm_panel *panel)
 {
-	if (panel && panel->funcs && panel->funcs->unprepare)
-		return panel->funcs->unprepare(panel);
+	if (!panel)
+		return -EINVAL;
 
-	return panel ? -ENOSYS : -EINVAL;
+	return drm_panel_change_state(panel, DRM_PANEL_POWER_PREPARED,
+		      DRM_PANEL_POWER_OFF,
+		      panel->funcs ? panel->funcs->unprepare : NULL);
 }
 EXPORT_SYMBOL(drm_panel_unprepare);
 
@@ -154,14 +178,19 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  * drivers. For smart panels it should still be possible to communicate with
  * the integrated circuitry via any command bus after this call.
  *
+ * Atomic framework will ensure that enable/disable are properly balanced.
+ * If this is not the case, a WARNING will be issued.
+ *
  * Return: 0 on success or a negative error code on failure.
  */
 int drm_panel_disable(struct drm_panel *panel)
 {
-	if (panel && panel->funcs && panel->funcs->disable)
-		return panel->funcs->disable(panel);
+	if (!panel)
+		return -EINVAL;
 
-	return panel ? -ENOSYS : -EINVAL;
+	return drm_panel_change_state(panel, DRM_PANEL_POWER_ENABLED,
+		      DRM_PANEL_POWER_PREPARED,
+		      panel->funcs ? panel->funcs->disable : NULL);
 }
 EXPORT_SYMBOL(drm_panel_disable);
 
@@ -173,14 +202,19 @@ EXPORT_SYMBOL(drm_panel_disable);
  * the panel. After this has completed it is possible to communicate with any
  * integrated circuitry via a command bus.
  *
+ * Atomic framework will ensure that prepare/unprepare are properly balanced.
+ * If this is not the case, a WARNING will be issued.
+ *
  * Return: 0 on success or a negative error code on failure.
  */
 int drm_panel_prepare(struct drm_panel *panel)
 {
-	if (panel && panel->funcs && panel->funcs->prepare)
-		return panel->funcs->prepare(panel);
+	if (!panel)
+		return -EINVAL;
 
-	return panel ? -ENOSYS : -EINVAL;
+	return drm_panel_change_state(panel, DRM_PANEL_POWER_OFF,
+		      DRM_PANEL_POWER_PREPARED,
+		      panel->funcs ? panel->funcs->prepare: NULL);
 }
 EXPORT_SYMBOL(drm_panel_prepare);
 
@@ -192,14 +226,19 @@ EXPORT_SYMBOL(drm_panel_prepare);
  * and the backlight to be enabled. Content will be visible on screen after
  * this call completes.
  *
+ * Atomic framework will ensure that enable/disable are properly balanced.
+ * If this is not the case, a WARNING will be issued.
+ *
  * Return: 0 on success or a negative error code on failure.
  */
 int drm_panel_enable(struct drm_panel *panel)
 {
-	if (panel && panel->funcs && panel->funcs->enable)
-		return panel->funcs->enable(panel);
+	if (!panel)
+		return -EINVAL;
 
-	return panel ? -ENOSYS : -EINVAL;
+	return drm_panel_change_state(panel, DRM_PANEL_POWER_PREPARED,
+		      DRM_PANEL_POWER_ENABLED,
+		      panel->funcs ? panel->funcs->enable: NULL);
 }
 EXPORT_SYMBOL(drm_panel_enable);
 
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 0a9442069d3c..7e6a552005d7 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -77,6 +77,18 @@ struct drm_panel_funcs {
 			   struct display_timing *timings);
 };
 
+/**
+ * enum drm_panel_state - describes the state of a panel
+ * @DRM_PANEL_POWER_OFF: panel is currently off (accessible from PREPARED)
+ * @DRM_PANEL_POWER_PREPARED: panel is prepared (accessible from OFF || ENABLED)
+ * @DRM_PANEL_POWER_ENABLED: panel is enabled  (accessible from PREPARED)
+ */
+enum drm_panel_state {
+	DRM_PANEL_POWER_OFF,
+	DRM_PANEL_POWER_PREPARED,
+	DRM_PANEL_POWER_ENABLED
+};
+
 /**
  * struct drm_panel - DRM panel object
  * @drm: DRM device owning the panel
@@ -84,6 +96,7 @@ struct drm_panel_funcs {
  * @dev: parent device of the panel
  * @funcs: operations that can be performed on the panel
  * @list: panel entry in registry
+ * @state: keeps track of the panel power status
  */
 struct drm_panel {
 	struct drm_device *drm;
@@ -93,6 +106,8 @@ struct drm_panel {
 	const struct drm_panel_funcs *funcs;
 
 	struct list_head list;
+
+	enum drm_panel_state state;
 };
 
 /**
-- 
2.15.0.rc1.287.g2b38de12cc-goog