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

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Date:	Tue, 4 Nov 2014 14:42:20 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Jingoo Han <jg1.han@...sung.com>
Cc:	'Heiko Stübner' <heiko@...ech.de>,
	'Bryan Wu' <cooloney@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: use of_find_backlight_by_node stub when
 backlight class disabled

On Tue, 04 Nov 2014, Jingoo Han wrote:

> On Tuesday, November 04, 2014 6:08 PM, Heiko Stübner wrote:
> > On Mon, 03 Nov 2014, Lee Jones wrote:
> > 
> > > On Wed, 29 Oct 2014, Heiko Stübner wrote:
> > >
> > > > Drivers may want to search for an optional backlight even when the backlight
> > > > class is disabled. In this case the linker would miss the function referenced
> > > > in the backlight header.
> > > >
> > > > Therefore use the stub function also when the backlight class is disabled.
> > > >
> > > > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > > > ---
> > > >  include/linux/backlight.h | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > Applied to Backlight -next with Jingoo's Ack.
> > 
> > I've removed this patch, as it causes unexpected:
> > 
> >   Redefinition of of_find_backlight_by_node()
> 
> I reproduced the same build error.
> 
> Then, how about folding the following two patches into
> one single patch? These two patches were already sent by Heiko Stübner.
> 
>   [PATCH] backlight: use of_find_backlight_by_node stub when backlight class disabled
>   [PATCH] backlight: extend of_find_backlight_by_node stub-check to modules
> 
> Then, the one single patch will do as follows.
> 
> -#ifdef CONFIG_OF
> +#if defined(CONFIG_OF) && (defined(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
> +			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
> 
> In this case, I cannot find any build errors.

That's a neat trick.  I didn't know you could do that.

However, it's bit messy consider different formatting, or a nested
#ifdef instead please.

> > ... error.
> > 
> > Bear in mind that defined(CONFIG_BACKLIGHT_CLASS_DEVICE) is false if
> > it's built in as a module.  Change to nested #ifdefs instead.
> > 
> > > > diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> > > > index adb14a8..d9cb644 100644
> > > > --- a/include/linux/backlight.h
> > > > +++ b/include/linux/backlight.h
> > > > @@ -157,7 +157,7 @@ struct generic_bl_info {
> > > >  	void (*kick_battery)(void);
> > > >  };
> > > >
> > > > -#ifdef CONFIG_OF
> > > > +#if defined(CONFIG_OF) && defined(CONFIG_BACKLIGHT_CLASS_DEVICE)
> > > >  struct backlight_device *of_find_backlight_by_node(struct device_node *node);
> > > >  #else
> > > >  static inline struct backlight_device *
> > >
> > 
> 

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