Re: [PATCH v4 1/4] backlight: introduce backlight_device_registered

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, October 08, 2013 02:39:58 PM Aaron Lu wrote:
> Introduce a new API for modules to query if a specific type of backlight
> device has been registered. This is useful for some backlight device
> provider module(e.g. ACPI video) to know if a native control
> interface(e.g. the interface created by i915) is available and then do
> things accordingly(e.g. avoid register its own on Win8 systems).
> 
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> Tested-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
> Tested-by: Yves-Alexis Perez <corsac@debian.org>
> Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/video/backlight/backlight.c | 31 +++++++++++++++++++++++++++++++
>  include/linux/backlight.h           |  4 ++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 94a403a..bf2d71d 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -21,6 +21,9 @@
>  #include <asm/backlight.h>
>  #endif
>  
> +static struct list_head bd_list_head;
> +static struct mutex bd_list_mutex;

I'd prefer these two things to be called backlight_dev_list and
backlight_dev_list_mutex, respectively.

> +
>  static const char *const backlight_types[] = {
>  	[BACKLIGHT_RAW] = "raw",
>  	[BACKLIGHT_PLATFORM] = "platform",
> @@ -349,10 +352,32 @@ struct backlight_device *backlight_device_register(const char *name,
>  	mutex_unlock(&pmac_backlight_mutex);
>  #endif
>  
> +	mutex_lock(&bd_list_mutex);
> +	list_add(&new_bd->entry, &bd_list_head);
> +	mutex_unlock(&bd_list_mutex);
> +
>  	return new_bd;
>  }
>  EXPORT_SYMBOL(backlight_device_register);
>  
> +bool backlight_device_registered(enum backlight_type type)
> +{
> +	bool found = false;
> +	struct backlight_device *bd;
> +
> +	mutex_lock(&bd_list_mutex);
> +	list_for_each_entry(bd, &bd_list_head, entry) {
> +		if (bd->props.type == type) {
> +			found = true;
> +			break;
> +		}
> +	}

Isn't it useful to be able to register more than one backlight device of the
same type sometimes?

> +	mutex_unlock(&bd_list_mutex);
> +
> +	return found;
> +}
> +EXPORT_SYMBOL(backlight_device_registered);
> +
>  /**
>   * backlight_device_unregister - unregisters a backlight device object.
>   * @bd: the backlight device object to be unregistered and freed.
> @@ -364,6 +389,10 @@ void backlight_device_unregister(struct backlight_device *bd)
>  	if (!bd)
>  		return;
>  
> +	mutex_lock(&bd_list_mutex);
> +	list_del(&bd->entry);
> +	mutex_unlock(&bd_list_mutex);
> +
>  #ifdef CONFIG_PMAC_BACKLIGHT
>  	mutex_lock(&pmac_backlight_mutex);
>  	if (pmac_backlight == bd)
> @@ -499,6 +528,8 @@ static int __init backlight_class_init(void)
>  
>  	backlight_class->dev_groups = bl_device_groups;
>  	backlight_class->pm = &backlight_class_dev_pm_ops;
> +	INIT_LIST_HEAD(&bd_list_head);
> +	mutex_init(&bd_list_mutex);
>  	return 0;
>  }
>  
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index 53b7794..5f9cd96 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -100,6 +100,9 @@ struct backlight_device {
>  	/* The framebuffer notifier block */
>  	struct notifier_block fb_notif;
>  
> +	/* list entry of all registered backlight devices */
> +	struct list_head entry;
> +
>  	struct device dev;
>  };
>  
> @@ -123,6 +126,7 @@ extern void devm_backlight_device_unregister(struct device *dev,
>  					struct backlight_device *bd);
>  extern void backlight_force_update(struct backlight_device *bd,
>  				   enum backlight_update_reason reason);
> +extern bool backlight_device_registered(enum backlight_type type);
>  
>  #define to_backlight_device(obj) container_of(obj, struct backlight_device, dev)

Thanks!

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