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

[Lee Jones]

> >> 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.
> 
> Agreed, which is why I send this set to all 3 the backlight maintainers
> directly on both postings.
> 
> What may be helpful for them is to hear from you if you're ok with the
> acpi-video bits which are actually going to use this, since those will
> be the only user of the new backlight api (for now).

I'm happy to apply any Backlight patches which have either Bryan or
Jingoo's Ack, as they are the reviewers for the BL subsystem.

> >> ---
> >>  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)
> >>  
> >>
> > 

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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