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backlight: backlight: Add overview and update existing doc

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Add overview chapter to backlight.c.

Update existing kernel-doc to follow a more consistent style and drop
kernel-doc for deprecated functions.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
This commit is contained in:
Sam Ravnborg 2020-07-19 10:07:34 +02:00 committed by Lee Jones
parent 9c4aa3118b
commit a1230eb2e3
1 changed files with 97 additions and 41 deletions
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138
drivers/video/backlight/backlight.c
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@ -22,6 +22,47 @@
#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;
@ -40,9 +81,17 @@ static const char *const backlight_scale_types[] = {
#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)
@ -324,7 +373,10 @@ ATTRIBUTE_GROUPS(bl_device);
* @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)
@ -337,20 +389,7 @@ void backlight_force_update(struct backlight_device *bd,
}
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)
@ -417,6 +456,15 @@ struct backlight_device *backlight_device_register(const char *name,
}
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;
@ -456,12 +504,7 @@ struct backlight_device *backlight_device_get_by_name(const char *name)
}
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)
@ -509,10 +552,12 @@ static int devm_backlight_device_match(struct device *dev, void *res,
* 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)
{
@ -524,10 +569,12 @@ EXPORT_SYMBOL(backlight_register_notifier);
* 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)
{
@ -536,19 +583,21 @@ 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.
*
* Managed backlight_device_register(). The backlight_device returned
* from this function are automatically freed on driver detach.
* See backlight_device_register() for more information.
* RETURNS:
*
* 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,
@ -576,13 +625,13 @@ struct backlight_device *devm_backlight_device_register(struct device *dev,
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)
@ -673,12 +722,19 @@ static void devm_backlight_release(void *data)
}
/**
* 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)
{