[UPSTREAM] Move backlight handling out of pcf50633 driver

Balaji Rao balajirrao at openmoko.org
Tue Oct 21 05:11:55 CEST 2008

On Mon, Oct 20, 2008 at 02:00:46PM +0100, Andy Green wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> | Andy Green wrote:
> |> Balaji, if you have some interest and time, please implement this 0-255
> |> in a patch and give it some small tries down /sys and see what the facts
> |> are.
> |
> | How does that help determine the impact to existing user code?
> Code that jut has the literal "64" in it for something that is variable
> can take this opportunity to get fixed.  Also note we are working up at
> *-tracking on this, so it is not going to be on peoples' devices
> overnight randomly.
> Werner's saying incrementing things will break with non 1:1 hardware
> step and logical backlight level.  Is it true, or just more "plausible
> bullshit"?  That is something that can be determined / fixed.

The voltage change effected by changing the brigtness value in /sys is
exponential, not linear.. So, the code that assumes that it's going to
reduce the brightness level by half by making it 30 or so, is actually
reducing it by 1/6 th.

I don't know if it's really important to have a linear brightness
scaling. If it is, the value 63 is arbitrary and is as good as any
other and there should be no reason against changing it in *-tracking.

	- Balaji

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