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 at 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)
--
1.9.0
