[Bug 67454] After suspend/resume, screen is black for all but the highest levels with i915 driver on MacBook Air 6,2

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=67454

--- Comment #85 from sam.attwell at gmail.com <sam.attwell at gmail.com> ---
(In reply to comment #81)
> (In reply to comment #79)
> > Thank you Patrick! Good work -  your module works great on my Macbook Air
> > 6.2 in EFI-Mode. (Kernel 3.13-rc3). I'd love to understand the actual
> > problem, did you figure out, why the standard backlight mechanism in i915
> > doesn't work?
> 
> I still don't understand what the actual problem is but the backlight driver
> (LP8550) that my module is controlling doesn't change any of it's settings
> after suspend. It takes a PWM signal on one of the input pins and that
> signal must be getting screwed up. How that pin is wired might be harder to
> figure out.
> 
> What my module does is to ignore that input pin and instead write the
> brightness value to an on-chip register and set it up so it becomes the
> source for the LP8550. I access the LP8550 over SMBUS through ACPI methods.
> It might be better to access the SMBUS directly but this was the fastest way
> to get something working.
> 
> If you find any bugs/issues with mba6x_bl please report it on github.

Hi Patrick,

Trying to make install from the git repository fails for me with:

"Can't read private key
  DEPMOD  3.11.0-15-generic
make[1]: Leaving directory `/usr/src/linux-headers-3.11.0-15-generic'"

Anything obvious i'm doing wrong?

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