From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Prisk Subject: Re: Devicetree node to turn off LCD when backlight is 'disabled' Date: Tue, 12 Feb 2013 21:26:34 +1300 Message-ID: <1360657594.3878.4.camel@gitbox> References: <1360563905.4130.6.camel@gitbox> <20130212070418.GC28850@avionic-0098.mockup.avionic-design.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130212070418.GC28850-RM9K5IK7kjIQXX3q8xo1gnVAuStQJXxyR5q1nwbD4aMs9pC9oP6+/A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Thierry Reding Cc: Devicetree Mailing List , Alexandre Courbot , Arm Kernel Mailing List List-Id: devicetree@vger.kernel.org On Tue, 2013-02-12 at 08:04 +0100, Thierry Reding wrote: > On Mon, Feb 11, 2013 at 07:25:05PM +1300, Tony Prisk wrote: > > I was just wondering if the following would be an acceptable way to turn > > off an lcd backlight when the pwm-backlight driver is set to level 0. > > The LCD backlight is 'powered' by the gpio. > > > > leds { > > compatible = "gpio-leds"; > > backlight { > > label = "lcd-power"; > > gpios = <&gpio 0 0 0>; /* bank pin active_low */ > > linux,default-trigger = "backlight"; > > default-state = "on"; > > }; > > }; > > > > The method has been tested by an end-user and confirmed as working - I > > just wanted to check whether it is the 'accepted' way of doing it. > > I don't quite see how this is related to pwm-backlight. Maybe you can > post a more complete example? Representing the backlight power as a GPIO > controlled LED seems somewhat kludgy. > > That said, there is currently no "accepted" way to use a GPIO to control > the power to the backlight in pwm-backlight. There was some work by Alex > (Cc'ed) to integrate this using generic power-sequences, but there was > some pushback on that. Your best bet currently would seem to integrate > this with the CDF (Common Display Framework). Unfortunately that'd mean > you'd need to write a whole new driver to abstract the panel. Even in > CDF there are ongoing discussions about how to hook it up with the > backlight framework. I know this doesn't give you a solution right away > but I think it's the best way to represent the actual hardware and it > takes into account a number of other aspect about displays as well. > > Thierry Just to clarify - I'm not looking for a way to do it immediately. The small snippet was sent as a patch to me by an end-user and although it worked, it just didn't 'feel' right so I thought I'd get a bit of feedback on it. Thanks for your thoughts. Regards Tony P