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
--- 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");
