[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 #81 from Patrik Jakobsson <patrik.r.jakobsson at gmail.com> ---
(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.

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