[Intel-gfx] Regression: Backlight not coming on after resume.

[Jani Nikula]

Hi James -

On Fri, 01 Mar 2013, James Courtier-Dutton <james.dutton at gmail.com> wrote:
>> James, try to revert that commit.  Does it fix?
>>
>> If so, you should check the output of intel_reg_dumper at broken and
>> working states.
>>
> Can someone point me to a datasheet that relates to this bit of code, so i
> can understand what all the registers do.
> I would like to understand the code in order to suggest a better fix.

https://01.org/linuxgraphics/documentation/driver-documentation-prms

Vol 3 is the relevant volume in each generation. I don't think any of
the docs back up the comments in the bad commit saying "BLC_PWM_CPU_CTL
is cleared to zero automatically when BLC_PWM_CPU_CTL2 and
BLC_PWM_PCH_CTL1 are written" though. I guess it could be some bad
ACPI/BIOS interaction too.

I'd still urge you to file the bug, and attach the dmesgs and register
dumps first. And let us know if the revert fixes it.


BR,
Jani.