Re: [PATCH 1/4] drm/i915: save/restore the legacy backlight control

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Aug 28, 2012 at 04:49:15PM +0200, Indan Zupancic wrote:
> On Tue, August 28, 2012 16:14, Daniel Vetter wrote:
> > On Tue, Aug 28, 2012 at 03:56:31PM +0200, Indan Zupancic wrote:
> >> Hello,
> >>
> >> On Tue, August 28, 2012 08:53, Jani Nikula wrote:
> >> > From: Daniel Vetter <daniel.vetter@ffwll.ch>
> >> >
> >> > This is a prep patch to stop drm/i915 from changing the LBPC registers
> >> > itself - but we still need to properly save/restore it on
> >> > suspend/resume.
> >> >
> >> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> >> > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> > ---
> [...]
> >> It seems weird that LBPC wouldn't be restored during resume by some BIOSes,
> >> is this really necessary?
> >
> > ba3820ade317ee36e496b9b40d2ec3987dd4aef0 claims so. But that commit
> > managed to put too many things into the same thing unfortunately.
> 
> Is that the right SHA? Because that just reverts my combination mode
> removal patch. Assuming it is the right commit, then I think it's
> incorrect in saying that it caused backlight dimming problems after
> resume. That particular problem was caused by a bogus shift. The
> problems caused by removing the mode was a lower max brightness
> and/or less brightness levels.

Yeah, right commit but imo with sub-par commit message. Your other mail
clarified things, thanks.

> By the way, saving LBPC only makes sense if it's done before it was
> set to 0 to disable the panel. I don't know if the current code does
> the right thing, I haven't looked at it for a while.

I think we can coax it into doing the right thing, see my other mail. If
your completely sure that lbpc /should/ be handled by the bios across s/r
I think we can drop this. But tbh I have no idea how this really is
supposed to work, and unfortunately we're not allowed to cross-check with
the windows driver codebase :(

Thanks, Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48