Some firmware drivers, ie acpi-video want to get themselves out of the way (in some cases) when their also is a raw backlight device available.
Due to module loading ordering being unknown, acpi-video cannot be certain that the backlight_device_registered(BACKLIGHT_RAW) it does for this is the final verdict wrt there being a BACKLIGHT_RAW device.
By adding notification acpi-video can listen for backlight devices showing up after it has loaded, and unregister its backlight device if desired.
Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/video/backlight/backlight.c | 40 +++++++++++++++++++++++++++++++++++++ include/linux/backlight.h | 7 +++++++ 2 files changed, 47 insertions(+)
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c index bd2172c..4280890 100644 --- a/drivers/video/backlight/backlight.c +++ b/drivers/video/backlight/backlight.c @@ -23,6 +23,7 @@
static struct list_head backlight_dev_list; static struct mutex backlight_dev_list_mutex; +static struct blocking_notifier_head backlight_notifier;
static const char *const backlight_types[] = { [BACKLIGHT_RAW] = "raw", @@ -370,6 +371,9 @@ struct backlight_device *backlight_device_register(const char *name, list_add(&new_bd->entry, &backlight_dev_list); mutex_unlock(&backlight_dev_list_mutex);
+ blocking_notifier_call_chain(&backlight_notifier, + BACKLIGHT_REGISTERED, new_bd); + return new_bd; } EXPORT_SYMBOL(backlight_device_register); @@ -413,6 +417,10 @@ void backlight_device_unregister(struct backlight_device *bd) pmac_backlight = NULL; mutex_unlock(&pmac_backlight_mutex); #endif + + blocking_notifier_call_chain(&backlight_notifier, + BACKLIGHT_UNREGISTERED, bd); + mutex_lock(&bd->ops_lock); bd->ops = NULL; mutex_unlock(&bd->ops_lock); @@ -438,6 +446,36 @@ 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. + */ +int backlight_register_notifier(struct notifier_block *nb) +{ + return blocking_notifier_chain_register(&backlight_notifier, nb); +} +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. + */ +int backlight_unregister_notifier(struct notifier_block *nb) +{ + return blocking_notifier_chain_unregister(&backlight_notifier, nb); +} +EXPORT_SYMBOL(backlight_unregister_notifier); + +/** * devm_backlight_device_register - resource managed backlight_device_register() * @dev: the device to register * @name: the name of the device @@ -544,6 +582,8 @@ static int __init backlight_class_init(void) backlight_class->pm = &backlight_class_dev_pm_ops; INIT_LIST_HEAD(&backlight_dev_list); mutex_init(&backlight_dev_list_mutex); + BLOCKING_INIT_NOTIFIER_HEAD(&backlight_notifier); + return 0; }
diff --git a/include/linux/backlight.h b/include/linux/backlight.h index 7264742..adb14a8 100644 --- a/include/linux/backlight.h +++ b/include/linux/backlight.h @@ -40,6 +40,11 @@ enum backlight_type { BACKLIGHT_TYPE_MAX, };
+enum backlight_notification { + BACKLIGHT_REGISTERED, + BACKLIGHT_UNREGISTERED, +}; + struct backlight_device; struct fb_info;
@@ -133,6 +138,8 @@ extern void devm_backlight_device_unregister(struct device *dev, extern void backlight_force_update(struct backlight_device *bd, enum backlight_update_reason reason); extern bool backlight_device_registered(enum backlight_type type); +extern int backlight_register_notifier(struct notifier_block *nb); +extern int backlight_unregister_notifier(struct notifier_block *nb);
#define to_backlight_device(obj) container_of(obj, struct backlight_device, dev)