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

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Message-ID: <20121116213420.GA27563@avionic-0098.mockup.avionic-design.de>
Date:	Fri, 16 Nov 2012 22:34:21 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Nov 16, 2012 at 01:16:45PM -0800, Andrew Morton wrote:
> 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 *
> _

Yes, that should work.

> > +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.

Yes, I should have thought about that. I'll add some proper kerneldoc
and repost.

Thanks for reviewing,
Thierry

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