Add overview chapter to backlight.c. Update existing kernel-doc to follow a more consistent style and drop kernel-doc for deprecated functions.
v4: - Include updated devm_of_find_backlight doc (was accidently included in a later patch)
v3: - Updated a few editorial details (Daniel)
v2: - Sevaral editorial corrections that makes reading much easier (Daniel) - Spelling fixes (Daniel) - updated intro chapter with a little more info
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 Cc: Lee Jones lee.jones@linaro.org Cc: Daniel Thompson daniel.thompson@linaro.org Cc: Jingoo Han jingoohan1@gmail.com --- drivers/video/backlight/backlight.c | 143 +++++++++++++++++++--------- 1 file changed, 100 insertions(+), 43 deletions(-)
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c index 7e249aa90b0e..db8717581ec5 100644 --- a/drivers/video/backlight/backlight.c +++ b/drivers/video/backlight/backlight.c @@ -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_brighness 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 platfrom 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 ioclt, 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) @@ -318,12 +367,15 @@ static struct attribute *bl_device_attrs[] = { ATTRIBUTE_GROUPS(bl_device);
/** - * backlight_force_update - tell the backlight subsystem that hardware state - * has changed + * backlight_force_update - force an update due to a hardware change * @bd: the backlight device to update + * @reason: the method used for the backlight 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) @@ -336,19 +388,7 @@ 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. - * - * 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) @@ -415,6 +455,15 @@ 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; @@ -454,12 +503,7 @@ 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) @@ -507,10 +551,12 @@ 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) { @@ -522,10 +568,12 @@ 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) { @@ -534,20 +582,22 @@ 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, const struct backlight_ops *ops, @@ -574,13 +624,13 @@ 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) @@ -671,12 +721,19 @@ 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) {