Devicetree node to turn off LCD when backlight is 'disabled'

[Thierry Reding]

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
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