[Intel-gfx] eDP display control registers in Linux kernel

[Jani Nikula]

On Thu, 26 Feb 2015, Michael Leuchtenburg <michael at slashhome.org> wrote:
> Okay, here's the results:
> 0000: 12 0a 02 41 00 00 00 00 00 00 00 00 00 0b 00
> 0070: 01 00
> 0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 0100: 0a 02 00 09 09 00 00 00 01 00 00
> 0200: 01 00 77 00 01 01 55 00
> 0600: 01
> 0700: 02
> 0701: 88 40 00 00
> 0720: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 0732: 00 00
>
> If I read that right, it looks like it is dynamic backlight capable - 0x702
> | (1 << 6).

That's correct, your panel is dynamic backlight *capable*, but the
dynamic backlight *enable* (bit 4 in 0x721) is not set. The power-on
default value is also disabled, and the i915 driver does not touch it
for sure.

It is of course (I wish it wasn't "of course") possible the BIOS enables
that in some circumstances; please try the dump again when you've
observed the brightness swings for sure, and check for the DBC enable
bit.

Also, are you sure the swings are content adaptive, and not ambient
light adaptive? Have you tried locating the ambient light sensor on the
laptop (possibly somewhere in the bezel around the display or keyboard)
and covering or ensuring constant lighting of it?


BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center