[Intel-gfx] 3.18.0-rc3: i915: eDP connected Display stays blank

[Arnd Hannemann]

Hi,

Am 06.11.2014 um 13:53 schrieb Jani Nikula:

>> root at kallisto:~# cat /sys/class/backlight/intel_backlight/bl_power
>> 1
>>
>>> you echo 0 there?
>>
>> :-) Works my display comes back, when I echo 0 there.
>>
>> Is user-space doing something wrong here?
> 
> If the userspace wishes to switch off backlight, then it's doing nothing
> wrong at all! ;)
> 
> Here's the story as I know it.
> 
> Once upon a time someone added the bl_power attribute to the sysfs class
> backlight interface. Even though the name implies a boolean backlight
> power, the values are in fact FB_BLANK_* from fb.h, and power on is
> FB_BLANK_UNBLANK, or 0. All the other values are various levels of
> blanking which make little sense to backlight, and thus any non-zero
> values mean power off. [1]
> 
> Until recently, intel_backlight of drm/i915 did not support bl_power at
> all. We ignored the attribute altogether. However changing bl_power from
> its default 0 did cause a backlight update hook to be called. In some
> edge cases doing this fixed some backlight issues by reprogramming the
> backlight intensity, and probably lead to the false assumption that
> bl_power needed to be set to 1 to enable power.
> 
> Now that we've enabled support for bl_power attribute (on eDP at least),
> the previously harmless, or sometimes even helpful, bl_power=1 actually
> does what it means. That is, switch off the backlight.
> 

Thanks for your elaborated answer.

> Please try this patch (untested) to find out the culprit.

Thanks, its the intel xorg driver:
[  255.777798] bl_power 1 by Xorg

I seems it was already corrected upstream, by Chris Wilson two days ago:
http://cgit.freedesktop.org/xorg/driver/xf86-video-intel/commit/?id=7ecc778691c452285f754743a93a46fa1d3da52f


Best regards
Arnd