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    SubjectRe: [PATCH v4 1/4] backlight: introduce backlight_device_registered
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    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.


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