backlight: Add backlight device (un)registration notification

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>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index bd2172c..4280890 100644 (file)
--- 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);
@@ -437,6 +445,36 @@ static int devm_backlight_device_match(struct device *dev, void *res,
        return *r == data;
 }
 
+/**
+ * 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
@@ -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 (file)
--- 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)