On Tue, 12 Feb 2013 16:35:56 +0900, Alex Courbot <[email protected]> wrote: > On 02/11/2013 03:25 PM, 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"; > > }; > > }; > > This would work... for the most common case of a FB blank event (as > gpio-leds will be notified of it and switch your GPIO on/off according > to the kind of event). There are a few drawbacks however: > > 1) You will have no control over the order of your power sequence. > pwm-backlight also uses FB notifications to switch the PWM on/off. Which > one will happen first will depend on the registration order. > > 2) This will only work on FB blank events. For instance, if someone > writes "0" into the "brightness" property of your backlight's sysfs > node, no FB blank event will be emitted and your GPIO will remain on. > > Also this solution works for the simple case where you control the > backlight using only a GPIO. It would be good to support more complex > cases as well (I have to handle a GPIO and a regulator, for instance). > > The "correct" way of doing this would be to let the pwm-backlight driver > (or even the backlight framework) control the power status of the > backlight itself. You can do this using the platform callbacks of > pwm-backlight, but this will require a custom panel. Another possibility > would be to use the power sequence framework within the backlight > drivers, but I need to rewrite it first.
That really does sound like the right approach, and wiring it up to a GPIO sounds reasonable. I don't think there is a need to use platform callbacks for this. g. _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
