linux-kernel - Re: [PATCH] backlight: Add of_find_backlight_by

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Message-Id: <20121116131645.c979837c.akpm@linux-foundation.org>
Date:	Fri, 16 Nov 2012 13:16:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	Richard Purdie <rpurdie@...ys.net>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: Add of_find_backlight_by_node() function

On Fri,  9 Nov 2012 15:04:38 +0100
Thierry Reding <thierry.reding@...onic-design.de> wrote:

> This function finds the struct backlight_device for a given device tree
> node. A dummy function is provided so that it safely compiles out if OF
> support is disabled.
> 
> Signed-off-by: Thierry Reding <thierry.reding@...onic-design.de>
> ---
>  drivers/video/backlight/backlight.c | 17 +++++++++++++++++
>  include/linux/backlight.h           | 10 ++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 297db2f..0d1ed4f 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -370,6 +370,23 @@ void backlight_device_unregister(struct backlight_device *bd)
>  }
>  EXPORT_SYMBOL(backlight_device_unregister);
>  
> +#if IS_ENABLED(CONFIG_OF)

Using IS_ENABLED() was odd.  We'll never support CONFIG_OF=m, so can't
we use plain old "#ifdef CONFIG_OF" here?

--- a/drivers/video/backlight/backlight.c~backlight-add-of_find_backlight_by_node-function-fix
+++ a/drivers/video/backlight/backlight.c
@@ -370,7 +370,7 @@ void backlight_device_unregister(struct 
 }
 EXPORT_SYMBOL(backlight_device_unregister);
 
-#if IS_ENABLED(CONFIG_OF)
+#ifdef CONFIG_OF
 static int of_parent_match(struct device *dev, void *data)
 {
 	return dev->parent && dev->parent->of_node == data;
--- a/include/linux/backlight.h~backlight-add-of_find_backlight_by_node-function-fix
+++ a/include/linux/backlight.h
@@ -134,7 +134,7 @@ struct generic_bl_info {
 	void (*kick_battery)(void);
 };
 
-#if IS_ENABLED(CONFIG_OF)
+#ifdef CONFIG_OF
 struct backlight_device *of_find_backlight_by_node(struct device_node *node);
 #else
 static inline struct backlight_device *
_


> +static int of_parent_match(struct device *dev, void *data)
> +{
> +	return dev->parent && dev->parent->of_node == data;
> +}
> +
> +struct backlight_device *of_find_backlight_by_node(struct device_node *node)
> +{
> +	struct device *dev;
> +
> +	dev = class_find_device(backlight_class, NULL, node, of_parent_match);
> +
> +	return dev ? to_backlight_device(dev) : NULL;
> +}
> +EXPORT_SYMBOL(of_find_backlight_by_node);

It's a global, exported-to-modules function.  We should document such
major interfaces.  Unless they are dead trivial, but I don't think this
one is that simple.  The semantics of the return value could be
explained, and callers should be told that of_find_backlight_by_node()
took a ref on the returned device, and that they need to run
put_device(retval->dev), if retval was not NULL.

And anything else which might be useful.


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