On Wednesday 23 January 2013 17:45:39 Alex Courbot wrote:
> > I'm confused. Why would you want to call into pwm_bl directly? If we're
> > going to split this up into separate platform devices, why not look up a
> > given backlight device and use the backlight API on that? The pieces of
> > the puzzle are all there: you can use of_find_backlight_by_node() to
> > obtain a backlight device from a device tree node, so I'd expect the DT
> > to look something like this:
> > backlight: backlight {
> >
> > compatible = "pwm-backlight";
> > ...
> >
> > };
>
> This would still prevent any power control from the backlight driver. I.e.
> if someone sets the brightness to 0 through sysfs, we cannot power the
> backlight off as pwm-backlight cannot control more than the PWM without
> platform callbacks. Backlight could only be powered off as a result of a fb
> blank event.
In order to solve this, how about adding a backlight notifier call chain to
broadcast backlight events in a fashion similar to what is done in
fbmem/fbcon? Then backlight_update_status() could send events like
BACKLIGHT_EARLY_EVENT_UPDATE and BACKLIGHT_EVENT_UPDATE to which panel drivers
could subscribe in order to power the backlight up and down as needed.
Then as the backlight is mentioned in the panel's DT node,
> panel: panel {
> compatible = "...";
> ...
> backlight = <&backlight>;
> ...
> };
the panel's driver could listen to backlight-related events and do its stuff
transparently, without changing anything to the backlight drivers. This would
be a good way to replace pwm-backlight's callbacks for platforms that use the
DT, and would also be applicable to any backlight class device.
Generally speaking, having a mean to monitor backlights state in the kernel
does not seem too crazy, especially since we already have a way to notify user
space through backlight_generate_event().
Richard, does that sound ok to you?
Alex.
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