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

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Message-ID: <20121116205636.GA27469@avionic-0098.mockup.avionic-design.de>
Date:	Fri, 16 Nov 2012 21:56:37 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jingoo Han <jg1.han@...sung.com>,
	'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 Thu, Nov 15, 2012 at 05:58:35PM +0900, Jingoo Han wrote:
> On Thursday, November 15, 2012 3:52 PM Thierry Reding wrote
> > On Thu, Nov 15, 2012 at 10:30:11AM +0900, Jingoo Han wrote:
> > > On Friday, November 09, 2012 11:05 PM Thierry Reding 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>
> > >
> > > CC'ed Andrew Morton
> > 
> > Yes, the backlight subsystem isn't very well maintained, so I should
> > have added Andrew in the first place. Thanks.
> > 
> > >
> > > Hi Thierry Reding,
> > >
> > > The patch itself looks good.
> > > Could you explain when this API is used?
> > > Thank you.
> > 
> > I use this for the upcoming Tegra DRM driver in order to hook up the
> > backlight with the DRM driver via DT to allow switching off the
> > backlight when the corresponding DRM output is switched of using DPMS.
> > Basically what you have is something like this in the device tree:
> > 
> > 	display {
> > 		...
> > 
> > 		backlight = <&backlight>;
> > 
> > 		...
> > 	}
> > 
> > Then you call something along these lines:
> > 
> > 	np = of_parse_phandle(display, "backlight", 0);
> > 	if (np) {
> > 		backlight = of_find_backlight_by_node(np);
> > 		of_node_put(np);
> > 	}
> > 
> > And then use the standard backlight API on the returned pointer.
> 
> OK, I see how this API can be called.
> AS you mentioned, it will allow Tegra DRM driver to use
> the backlight driver.
> 
> Acked-by: Jingoo Han <jg1.han@...sung.com>

Andrew,

any chance we could still get this in for the 3.8 merge window?

Thierry

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