Re: PWM and backlight devices

[Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 12/06/2011 09:07 AM, Thierry Reding wrote:
> Hi,
> 
> I'm working on adding support for a device which is booted from a device tree
> only. Currently this gets me to a login prompt on a serial console and the
> device is basically functional. However, the device also has a display with a
> backlight that is controlled via a PWM (supplied by the SoC). If this was a
> regular board it would be simple to implement this via the pwm-backlight
> driver.
> 
> Unfortunately, the pwm-backlight driver doesn't have device tree support yet
> and I'm not sure how to best implement it. As far as I can see, I would first
> need to have some way of representing a PWM device in the DT that I could
> reference in the pwm-backlight device node and I would need to add actual DT
> support to pwm-backlight. Implementing support for the data passed in the
> platform data should be rather straightforward, but I don't see how the
> callback functions could be represented in the DT.
> 
> For some setups it would probably be enough to just specify the used PWM, but
> other boards fiddle with some GPIOs in the callbacks and I guess that could
> be represented by adding a "gpios" property with a list of pins that need to
> be toggled for example when the backlight power is enabled/disabled.
> 
> Has anyone done something similar yet? Am I even on the right track here?
> 

I haven't seen anything. Perhaps something similar to how the gpio-keys
binding is done would work here. This could have a phandle to the pwm
device similar to gpios.

Rob