Hi,
Am 06.11.2014 um 13:53 schrieb Jani Nikula:
root@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=7ecc7786...
Best regards Arnd