[UPSTREAM] Move backlight handling out of pcf50633 driver

[Balaji Rao]

On Sun, Oct 19, 2008 at 10:24:22AM +0100, Andy Green wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Somebody in the thread at some point said:
>
> Nice work Balaji.
>
Andy,

Thank you.
> | Can you make the max brightness a #define where it can be an arbitrary
> | value such as 100 or 255? I'm also curious about suspend/resume ordering
>
> This will be more important than it sounds.  How about we ourselves
> change to 255 as the logical max brightness.  Existing code can find our
> actual max brightness down /sys and scale accordingly.

Hmmm.. Are we sure we need to do this ? I'm mildly interested in it
because the max_brightness is exported as well and any good userspace code
that tries to control the backlight must read the max_brightness value.

> | and turning on the lcd backlight. You need to make sure the lcds are on
> | before the backlight to prevent white screen flashes and should turn off
> | backlight before the lcds.
>
> Ah Balaji has taken care about it I see, he has added a probe completion
> callback into mach_gta02.c that creates the backlight device and forces
> its parent to the jbt6k74.  So if I have it right the full device
> subtree there is like this
>
> i2c bus ->
> ~  pcf50633 ->
> ~    Glamo ->
> ~      Glamo fb ->
> ~        Glamo SPI bb bus ->
> ~          jbt6k74 ->
> ~             backlight
>
> That looks great for not only killing races but also avoiding white flash.

Yes, it helps a great deal. I've found the same patch to break on
stable-tracking but works perfectly on andy-tracking.

One more thing, I think I noticed  a LEDPWRFAIL interrupt generated
when the brightness is changed. I think this happens because
of the led ramp. The output value stays lower than 90% of the target
value for longer than the debounce time which is 100ms by default.(Table
42) So, as I understand, when the led_dimstep has a value of 5, it takes
about 2.5 ms for the voltage to reach the target. I'm wondering how can
this happen ? Can anyone shed some light on this ?

	- Balaji