backlight: backlight: Add overview and update existing doc

#include <asm/backlight.h>

#endif

/**

 * DOC: overview

 *

 * The backlight core supports implementing backlight drivers.

 *

 * A backlight driver registers a driver using

 * devm_backlight_device_register(). The properties of the backlight

 * driver such as type and max_brightness must be specified.

 * When the core detect changes in for example brightness or power state

 * the update_status() operation is called. The backlight driver shall

 * implement this operation and use it to adjust backlight.

 *

 * Several sysfs attributes are provided by the backlight core::

 *

 * - brightness         R/W, set the requested brightness level

 * - actual_brightness  RO, the brightness level used by the HW

 * - max_brightness     RO, the maximum  brightness level supported

 *

 * See Documentation/ABI/stable/sysfs-class-backlight for the full list.

 *

 * The backlight can be adjusted using the sysfs interface, and

 * the backlight driver may also support adjusting backlight using

 * a hot-key or some other platform or firmware specific way.

 *

 * The driver must implement the get_brightness() operation if

 * the HW do not support all the levels that can be specified in

 * brightness, thus providing user-space access to the actual level

 * via the actual_brightness attribute.

 *

 * When the backlight changes this is reported to user-space using

 * an uevent connected to the actual_brightness attribute.

 * When brightness is set by platform specific means, for example

 * a hot-key to adjust backlight, the driver must notify the backlight

 * core that brightness has changed using backlight_force_update().

 *

 * The backlight driver core receives notifications from fbdev and

 * if the event is FB_EVENT_BLANK and if the value of blank, from the

 * FBIOBLANK ioctrl, results in a change in the backlight state the

 * update_status() operation is called.

 */

static struct list_head backlight_dev_list;

static struct mutex backlight_dev_list_mutex;

static struct blocking_notifier_head backlight_notifier;

#if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \

			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))

/* This callback gets called when something important happens inside a

 * framebuffer driver. We're looking if that important event is blanking,

 * and if it is and necessary, we're switching backlight power as well ...

/*

 * fb_notifier_callback

 *

 * This callback gets called when something important happens inside a

 * framebuffer driver. The backlight core only cares about FB_BLANK_UNBLANK

 * which is reported to the driver using backlight_update_status()

 * as a state change.

 *

 * There may be several fbdev's connected to the backlight device,

 * in which case they are kept track of. A state change is only reported

 * if there is a change in backlight for the specified fbdev.

 */

static int fb_notifier_callback(struct notifier_block *self,

				unsigned long event, void *data)

 * @reason: reason for update

 *

 * Updates the internal state of the backlight in response to a hardware event,

 * and generate a uevent to notify userspace

 * and generates an uevent to notify userspace. A backlight driver shall call

 * backlight_force_update() when the backlight is changed using, for example,

 * a hot-key. The updated brightness is read using get_brightness() and the

 * brightness value is reported using an uevent.

 */

void backlight_force_update(struct backlight_device *bd,

			    enum backlight_update_reason reason)

}

EXPORT_SYMBOL(backlight_force_update);

/**

 * backlight_device_register - create and register a new object of

 *   backlight_device class.

 * @name: the name of the new object(must be the same as the name of the

 *   respective framebuffer device).

 * @parent: a pointer to the parent device

 * @devdata: an optional pointer to be stored for private driver use. The

 *   methods may retrieve it by using bl_get_data(bd).

 * @ops: the backlight operations structure.

 * @props: pointer to backlight's properties structure.

 *

 * Creates and registers new backlight device. Returns either an

 * ERR_PTR() or a pointer to the newly allocated device.

 */

/* deprecated - use devm_backlight_device_register() */

struct backlight_device *backlight_device_register(const char *name,

	struct device *parent, void *devdata, const struct backlight_ops *ops,

	const struct backlight_properties *props)

}

EXPORT_SYMBOL(backlight_device_register);

/** backlight_device_get_by_type - find first backlight device of a type

 * @type: the type of backlight device

 *

 * Look up the first backlight device of the specified type

 *

 * RETURNS:

 *

 * Pointer to backlight device if any was found. Otherwise NULL.

 */

struct backlight_device *backlight_device_get_by_type(enum backlight_type type)

{

	bool found = false;

}

EXPORT_SYMBOL(backlight_device_get_by_name);

/**

 * backlight_device_unregister - unregisters a backlight device object.

 * @bd: the backlight device object to be unregistered and freed.

 *

 * Unregisters a previously registered via backlight_device_register object.

 */

/* deprecated - use devm_backlight_device_unregister() */

void backlight_device_unregister(struct backlight_device *bd)

{

	if (!bd)

 * backlight_register_notifier - get notified of backlight (un)registration

 * @nb: notifier block with the notifier to call on backlight (un)registration

 *

 * @return 0 on success, otherwise a negative error code

 *

 * Register a notifier to get notified when backlight devices get registered

 * or unregistered.

 *

 * RETURNS:

 *

 * 0 on success, otherwise a negative error code

 */

int backlight_register_notifier(struct notifier_block *nb)

{

 * backlight_unregister_notifier - unregister a backlight notifier

 * @nb: notifier block to unregister

 *

 * @return 0 on success, otherwise a negative error code

 *

 * Register a notifier to get notified when backlight devices get registered

 * or unregistered.

 *

 * RETURNS:

 *

 * 0 on success, otherwise a negative error code

 */

int backlight_unregister_notifier(struct notifier_block *nb)

{

EXPORT_SYMBOL(backlight_unregister_notifier);

/**

 * devm_backlight_device_register - resource managed backlight_device_register()

 * devm_backlight_device_register - register a new backlight device

 * @dev: the device to register

 * @name: the name of the device

 * @parent: a pointer to the parent device

 * @parent: a pointer to the parent device (often the same as @dev)

 * @devdata: an optional pointer to be stored for private driver use

 * @ops: the backlight operations structure

 * @props: the backlight properties

 *

 * @return a struct backlight on success, or an ERR_PTR on error

 * Creates and registers new backlight device. When a backlight device

 * is registered the configuration must be specified in the @props

 * parameter. See description of &backlight_properties.

 *

 * RETURNS:

 *

 * Managed backlight_device_register(). The backlight_device returned

 * from this function are automatically freed on driver detach.

 * See backlight_device_register() for more information.

 * struct backlight on success, or an ERR_PTR on error

 */

struct backlight_device *devm_backlight_device_register(struct device *dev,

	const char *name, struct device *parent, void *devdata,

EXPORT_SYMBOL(devm_backlight_device_register);

/**

 * devm_backlight_device_unregister - resource managed backlight_device_unregister()

 * devm_backlight_device_unregister - unregister backlight device

 * @dev: the device to unregister

 * @bd: the backlight device to unregister

 *

 * Deallocated a backlight allocated with devm_backlight_device_register().

 * Deallocates a backlight allocated with devm_backlight_device_register().

 * Normally this function will not need to be called and the resource management

 * code will ensure that the resource is freed.

 * code will ensure that the resources are freed.

 */

void devm_backlight_device_unregister(struct device *dev,

				struct backlight_device *bd)

}

/**

 * devm_of_find_backlight - Resource-managed of_find_backlight()

 * @dev: Device

 * devm_of_find_backlight - find backlight for a device

 * @dev: the device

 *

 * Device managed version of of_find_backlight().

 * The reference on the backlight device is automatically

 * This function looks for a property named 'backlight' on the DT node

 * connected to @dev and looks up the backlight device. The lookup is

 * device managed so the reference to the backlight device is automatically

 * dropped on driver detach.

 *

 * RETURNS:

 *

 * A pointer to the backlight device if found.

 * Error pointer -EPROBE_DEFER if the DT property is set, but no backlight

 * device is found. NULL if there's no backlight property.

 */

struct backlight_device *devm_of_find_backlight(struct device *dev)

{