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

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Message-id: <001201cdc30f$65a17be0$30e473a0$%han@samsung.com>
Date:	Thu, 15 Nov 2012 17:58:35 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Thierry Reding' <thierry.reding@...onic-design.de>
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 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>


Best regards,
Jingoo Han

> 
> Thierry

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