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

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Message-ID: <20121115065140.GA21208@avionic-0098.mockup.avionic-design.de>
Date:	Thu, 15 Nov 2012 07:51:40 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Jingoo Han <jg1.han@...sung.com>
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'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 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.

Thierry

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