[PATCH v1 02/26] drm/panel: add backlight support

[Sam Ravnborg]

Panels often supports backlight as specified in a device tree.
Update the drm_panel infrastructure to support this to
simplify the drivers.

With this the panel driver just needs to add the following to the
probe() function:

    err = drm_panel_of_backlight(panel);
    if (err)
            return err;

Then drm_panel will handle all the rest.

v2:
- Drop test of CONFIG_DRM_PANEL in header-file (Laurent)
- do not enable backlight if ->enable() returns an error

Signed-off-by: Sam Ravnborg <sam at ravnborg.org>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <maxime.ripard at bootlin.com>
Cc: Sean Paul <sean at poorly.run>
Cc: Thierry Reding <thierry.reding at gmail.com>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: David Airlie <airlied at linux.ie>
Cc: Daniel Vetter <daniel at ffwll.ch>
---
 drivers/gpu/drm/drm_panel.c | 49 +++++++++++++++++++++++++++++++++++--
 include/drm/drm_panel.h     | 23 +++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 2d59cdd05e50..35609c90e467 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/backlight.h>
 #include <linux/err.h>
 #include <linux/module.h>
 
@@ -196,13 +197,18 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  */
 int drm_panel_enable(struct drm_panel *panel)
 {
+	int ret = 0;
+
 	if (!panel)
 		return -EINVAL;
 
 	if (panel->funcs && panel->funcs->enable)
-		return panel->funcs->enable(panel);
+		ret = panel->funcs->enable(panel);
 
-	return 0;
+	if (ret >= 0)
+		backlight_enable(panel->backlight);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_panel_enable);
 
@@ -221,6 +227,8 @@ int drm_panel_disable(struct drm_panel *panel)
 	if (!panel)
 		return -EINVAL;
 
+	backlight_disable(panel->backlight);
+
 	if (panel->funcs && panel->funcs->disable)
 		return panel->funcs->disable(panel);
 
@@ -289,6 +297,43 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
 EXPORT_SYMBOL(of_drm_find_panel);
 #endif
 
+#ifdef CONFIG_BACKLIGHT_CLASS_DEVICE
+/**
+ * drm_panel_of_backlight - use backlight device node for backlight
+ * @panel: DRM panel
+ *
+ * Use this function to enable backlight handling if your panel
+ * uses device tree and has a backlight handle.
+ *
+ * When panel is enabled backlight will be enabled after a
+ * successfull call to &drm_panel_funcs.enable()
+ *
+ * When panel is disabled backlight will be disabled before the
+ * call to &drm_panel_funcs.disable().
+ *
+ * A typical implementation for a panel driver supporting device tree
+ * will call this function and then backlight just works.
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int drm_panel_of_backlight(struct drm_panel *panel)
+{
+	struct backlight_device *backlight;
+
+	if (!panel || !panel->dev)
+		return -EINVAL;
+
+	backlight = devm_of_find_backlight(panel->dev);
+
+	if (IS_ERR(backlight))
+                return PTR_ERR(backlight);
+
+	panel->backlight = backlight;
+	return 0;
+}
+EXPORT_SYMBOL(drm_panel_of_backlight);
+#endif
+
 MODULE_AUTHOR("Thierry Reding <treding at nvidia.com>");
 MODULE_DESCRIPTION("DRM panel infrastructure");
 MODULE_LICENSE("GPL and additional rights");
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index ce8da64022b4..d30c98567384 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -28,6 +28,7 @@
 #include <linux/errno.h>
 #include <linux/list.h>
 
+struct backlight_device;
 struct device_node;
 struct drm_connector;
 struct drm_device;
@@ -59,6 +60,10 @@ struct display_timing;
  *
  * To save power when no video data is transmitted, a driver can power down
  * the panel. This is the job of the .unprepare() function.
+ *
+ * Backlight can be handled automatically if configured using
+ * drm_panel_of_backlight(). Then the driver do not need to implement the
+ * functionality to enable/disable backlight.
  */
 struct drm_panel_funcs {
 	/**
@@ -132,6 +137,15 @@ struct drm_panel {
 	 */
 	struct device *dev;
 
+	/**
+	 * @backlight:
+	 *
+	 * Backlight device, used to turn on backlight after
+	 * the call to enable(), and to turn off
+	 * backlight before call to disable().
+	 */
+	struct backlight_device *backlight;
+
 	/**
 	 * @funcs:
 	 *
@@ -183,4 +197,13 @@ static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
+int drm_panel_of_backlight(struct drm_panel *panel);
+#else
+static inline int drm_panel_of_backlight(struct drm_panel *panel)
+{
+	return -EINVAL;
+}
+#endif
+
 #endif
-- 
2.20.1