Questions on adding backlight support for the i915 driver

[Elizabeth Myers]

On 01/30/15 19:31, Adrian Chadd wrote:
> So, this is one of the discussions that popped up in the linux side of
> things, that we will end up eventually pulling into freebsd when the
> i915 code is updated.
> 
> The raw value is (a) different per setup, and (b) may be inverted to
> work correctly.
> 
> I also don't know if linear values along that spectrum map to linear
> brightness levels.
> 
> So yeah, my suggestion we expose an ACPI/acpi_video like list of valid
> percentages, and let the user set them from 0-100%. That way the
> details of how the actual backlight values get derived are hidden from
> userland.
> 
> 
> 
> -adrian


I have a sort of "rough draft" of this. I've tested all the percentages
(Ivy Bridge) and they do seem to correlate linearly (and to the
intel_backlight userland program used by a lot of people). I haven't
been able to test on any other hardware as I don't have it, and I don't
know what chipsets require the value to be inverted, so I've not
implemented that.

If anyone else would like to help test, it'd be nice.

--
Cheers,
Elizabeth
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