[Bug 72289] [GM45 backlight] LCD waterfall effect on HP 2230s laptop

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=72289

--- Comment #25 from Jani Nikula <jani.nikula at intel.com> ---
Joonas, ping for updates.

(In reply to comment #20)
> Well, that was an excellent discovery.
> 
> It seems that the latter one (0x61254 0x15cc07c6) simply fixes the problem
> completely.
> 
> I'm not sure if the former one plays any role of importance here.

It might make a crucial difference, since register 0x61250 bit 30 that's set in
your reg dump but not in Daniel's suggestion (presumably based on Windows) is
the "combination mode". Register 0x61254 has backlight modulation frequency and
duty cycle. So I'd very much like you to try:

# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61250 0x80000000

and see if that fixes the issue. If not, I'd like you to reboot, and try:

# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61254 0x15cc07c6 &&
intel_reg_write 0x61250 0xc0000000

(All on one command line just because one at a time you'll get a black screen
and it'll be hard to continue ;)

Finally it would be nice to retest on v3.14 or later because we changed the
backlight code considerably, and further debugging will be easier on the recent
code base.

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