eDP display control registers in Linux kernel

[Michael Leuchtenburg]

On Mon, Feb 23, 2015 at 2:59 AM, Jani Nikula <jani.nikula at intel.com> wrote:

>
> Hi Michael -
>
> Please always cc: the relevant mailing lists; done now.
>

Sorry, will do; thanks.


>
> On Sun, 22 Feb 2015, Michael Leuchtenburg <michael at slashhome.org> wrote:
> > Hi Jani,
> >
> > I've been trying to figure out how to control the dynamic backlight
> control
> > on my new Dell XPS 13 since the defaults are atrocious - huge swings in
> > brightness from a black background to a white one, over a few seconds
> > period so it's very obvious. I eventually tracked down a patch from the
> > Chromium folks that adds a sysfs interface (
> >
> https://chromium.googlesource.com/chromiumos/third_party/kernel/+/db5eacd6ac7a0cbda4ea1010fabbd3ff6b30e0bc%5E%21/
> ),
> > but it seems to depend on your patch that adds eDP display control
> > registers (
> >
> http://lists.freedesktop.org/archives/dri-devel/2013-November/049098.html
> ),
> > which was never merged into mainline as far as I can tell.
> >
> > Do you know what the status of that is? Is it still wending its way
> through
> > the process (now, over a year later) or did it die somewhere along the
> way?
> > The patch doesn't apply to mainline today, though it's simple enough
> that I
> > suspect it'd be easy to adapt. I'd rather see where it went, though.
> >
> > I'd appreciate any help you can offer.
>
> The Chrome OS patches wouldn't be acceptable upstream, and indeed
> they've never been posted upstream. A more driver agnostic approach
> would be required.
>
> My patches were simple, adding some macros etc. They were reviewed but
> apparently forgotten, also by me. I'll repost them, but they won't do
> you much good in this case.
>
> I'm also not convinced yet that your problem would be solved by the
> patches; are you sure Dell XPS 13 does have dynamic backlight control in
> the panel, adjustable via DPCD?
>

I'm certain that it has dynamic backlight control of some sort, as the
brightness varies based on content. I'm also sure it has an eDP panel, and
an Intel graphics adapter. I'm not certain that DPCD will let me adjust it,
or how to check, though the ChromeOS patch seems to assume that intel + edp
-> DBC adjustable via DPCD.

Michael
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