Commit 152dbdea authored by Sam Ravnborg's avatar Sam Ravnborg
Browse files

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: default avatarSam Ravnborg <sam@ravnborg.org>
Reviewed-by: default avatarLaurent 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
parent 5dce87a9

drivers/gpu/drm/drm_panel.c

+60 −2
Original line number Diff line number Diff line
@@ -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");

include/drm/drm_panel.h

+25 −0
Original line number Diff line number Diff line
@@ -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

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