drm/panel: add backlight support

Panels often support 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.

There is one caveat with the backlight support.
If drm_panel_(enable|disable) are called multiple times
in a row then backlight_(enable|disable) will be called multiple times.

The above will happen when a panel drivers unconditionally
calls drm_panel_disable() in their shutdown() function,
whan the panel is already disabled and then shutdown() is called.

Reading the backlight code it seems safe to call
the backlight_(enable|disable) several times.

v3:
- Improve comments, fix grammar (Laurent)
- Do not fail in drm_panel_of_backlight() if no DT support (Laurent)
- Log if backlight_(enable|disable) fails (Laurent)
- Improve drm_panel_of_backlight() docs
- Updated changelog with backlight analysis (triggered by Laurent)

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@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191207140353.23967-3-sam@ravnborg.org

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 4ab7229..a5e4084 100644 (file)
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -21,11 +21,13 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/backlight.h>
 #include <linux/err.h>
 #include <linux/module.h>
 
 #include <drm/drm_crtc.h>
 #include <drm/drm_panel.h>
+#include <drm/drm_print.h>
 
 static DEFINE_MUTEX(panel_lock);
 static LIST_HEAD(panel_list);
@@ -196,11 +198,21 @@ EXPORT_SYMBOL(drm_panel_unprepare);
  */
 int drm_panel_enable(struct drm_panel *panel)
 {
+       int ret;
+
        if (!panel)
                return -EINVAL;
 
-       if (panel->funcs && panel->funcs->enable)
-               return panel->funcs->enable(panel);
+       if (panel->funcs && panel->funcs->enable) {
+               ret = panel->funcs->enable(panel);
+               if (ret < 0)
+                       return ret;
+       }
+
+       ret = backlight_enable(panel->backlight);
+       if (ret < 0)
+               DRM_DEV_INFO(panel->dev, "failed to enable backlight: %d\n",
+                            ret);
 
        return 0;
 }
@@ -218,9 +230,16 @@ EXPORT_SYMBOL(drm_panel_enable);
  */
 int drm_panel_disable(struct drm_panel *panel)
 {
+       int ret;
+
        if (!panel)
                return -EINVAL;
 
+       ret = backlight_disable(panel->backlight);
+       if (ret < 0)
+               DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
+                            ret);
+
        if (panel->funcs && panel->funcs->disable)
                return panel->funcs->disable(panel);
 
@@ -289,6 +308,45 @@ 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 phandle.
+ *
+ * When the panel is enabled backlight will be enabled after a
+ * successful call to &drm_panel_funcs.enable()
+ *
+ * When the 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 at probe time. Backlight will then be handled
+ * transparently without requiring any intervention from the driver.
+ * drm_panel_of_backlight() must be called after the call to drm_panel_init().
+ *
+ * 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@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 2bd1d80..54b5576 100644 (file)
--- 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 does not need to implement the
+ * functionality to enable/disable backlight.
  */
 struct drm_panel_funcs {
        /**
@@ -144,6 +149,17 @@ 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 the call to
+        * disable().
+        * backlight is set by drm_panel_of_backlight() and drivers
+        * shall not assign it.
+        */
+       struct backlight_device *backlight;
+
        /**
         * @funcs:
         *
@@ -195,4 +211,13 @@ 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 0;
+}
+#endif
+
 #endif