[PATCH 1/2] backlight: add devm_backlight_device_{register,unregister}()

[PATCH 1/2] backlight: add devm_backlight_device_{register,unregister}()

[Jingoo Han]

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These functions allow the driver core to automatically clean up any
allocation made by backlight drivers. Thus it simplifies the error
paths.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
---
 drivers/video/backlight/backlight.c |   75 +++++++++++++++++++++++++++++++++++
 include/linux/backlight.h           |    6 +++
 2 files changed, 81 insertions(+)

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index c74e7aa..feb68af 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -370,6 +370,81 @@ void backlight_device_unregister(struct backlight_device *bd)
 }
 EXPORT_SYMBOL(backlight_device_unregister);
 
+static void devm_backlight_device_release(struct device *dev, void *res)
+{
+	struct backlight_device *backlight = *(struct backlight_device **)res;
+
+	backlight_device_unregister(backlight);
+}
+
+static int devm_backlight_device_match(struct device *dev, void *res,
+					void *data)
+{
+	struct backlight_device **r = res;
+
+	return *r == data;
+}
+
+/**
+ * devm_backlight_device_register - resource managed backlight_device_register()
+ * @dev: the device to register
+ * @name: the name of the device
+ * @parent: a pointer to the parent device
+ * @devdata: an optional pointer to be stored for private driver use
+ * @ops: the backlight operations structure
+ * @props: the backlight properties
+ *
+ * @return a struct backlight on success, or an ERR_PTR on error
+ *
+ * Managed backlight_device_register(). The backlight_device returned
+ * from this function are automatically freed on driver detach.
+ * See backlight_device_register() for more information.
+ */
+struct backlight_device *devm_backlight_device_register(struct device *dev,
+	const char *name, struct device *parent, void *devdata,
+	const struct backlight_ops *ops,
+	const struct backlight_properties *props)
+{
+	struct backlight_device **ptr, *backlight;
+
+	ptr = devres_alloc(devm_backlight_device_release, sizeof(*ptr),
+			GFP_KERNEL);
+	if (!ptr)
+		return ERR_PTR(-ENOMEM);
+
+	backlight = backlight_device_register(name, parent, devdata, ops,
+						props);
+	if (!IS_ERR(backlight)) {
+		*ptr = backlight;
+		devres_add(dev, ptr);
+	} else {
+		devres_free(ptr);
+	}
+
+	return backlight;
+}
+EXPORT_SYMBOL(devm_backlight_device_register);
+
+/**
+ * devm_backlight_device_unregister - resource managed backlight_device_unregister()
+ * @dev: the device to unregister
+ * @bd: the backlight device to unregister
+ *
+ * Deallocated a backlight allocated with devm_backlight_device_register().
+ * Normally this function will not need to be called and the resource management
+ * code will ensure that the resource is freed.
+ */
+void devm_backlight_device_unregister(struct device *dev,
+				struct backlight_device *bd)
+{
+	int rc;
+
+	rc = devres_release(dev, devm_backlight_device_release,
+				devm_backlight_device_match, bd);
+	WARN_ON(rc);
+}
+EXPORT_SYMBOL(devm_backlight_device_unregister);
+
 #ifdef CONFIG_OF
 static int of_parent_match(struct device *dev, const void *data)
 {
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index da9a082..53b7794 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -114,7 +114,13 @@ static inline void backlight_update_status(struct backlight_device *bd)
 extern struct backlight_device *backlight_device_register(const char *name,
 	struct device *dev, void *devdata, const struct backlight_ops *ops,
 	const struct backlight_properties *props);
+extern struct backlight_device *devm_backlight_device_register(
+	struct device *dev, const char *name, struct device *parent,
+	void *devdata, const struct backlight_ops *ops,
+	const struct backlight_properties *props);
 extern void backlight_device_unregister(struct backlight_device *bd);
+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);
 
-- 
1.7.10.4

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Re: [PATCH 1/2] backlight: add devm_backlight_device_{register,unregister}()

[Andrew Morton]

On Thu, 16 May 2013 05:28:26 +0000 (GMT) Jingoo Han <jg1.han@samsung.com> wrote:

> These functions allow the driver core to automatically clean up any
> allocation made by backlight drivers. Thus it simplifies the error
> paths.
> 
> ...
>
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -370,6 +370,81 @@ void backlight_device_unregister(struct backlight_device *bd)
>  }
>  EXPORT_SYMBOL(backlight_device_unregister);
>  
> +static void devm_backlight_device_release(struct device *dev, void *res)
> +{
> +	struct backlight_device *backlight = *(struct backlight_device **)res;
> +
> +	backlight_device_unregister(backlight);
> +}
>
> ...
>
> +struct backlight_device *devm_backlight_device_register(struct device *dev,
> +	const char *name, struct device *parent, void *devdata,
> +	const struct backlight_ops *ops,
> +	const struct backlight_properties *props)
> +{
> +	struct backlight_device **ptr, *backlight;
> +
> +	ptr = devres_alloc(devm_backlight_device_release, sizeof(*ptr),
> +			GFP_KERNEL);

Well this is an awkward-looking thing.  We allocate a silly little 4-
or 8-byte object just to track the backlight_device* via the devres
system.

I assume this was done so that devres could be used as a wrapper around
the existing code?  

Really it would be better if things like backlight_device_register()
were themselves directly converted to use devm_foo(), yes?