[UPSTREAM] Move backlight handling out of pcf50633 driver

Mark Brown broonie at opensource.wolfsonmicro.com
Tue Oct 21 11:04:15 CEST 2008

On Tue, Oct 21, 2008 at 08:41:55AM +0530, Balaji Rao wrote:

> 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.

The human eye doesn't detect brightness linearly so hardware intended
for use in controlling brightness often implements controls with
non-linear values like this - check what the actual effect is for the

> 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.

User interfaces for adjusting brightness should be assuming linear
brightness as experienced by users so things like sliders to set the
level would end up appearing to not work well.

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