[PATCH resend 2/4] backlight: Add backlight device (un)registration notification

[Rafael J. Wysocki]

On Wednesday, May 21, 2014 03:39:54 PM Hans de Goede wrote:
> 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>

Backlight maintainer's ACK is requisite here.

> ---
>  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)
>  
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.