[Bug 80773] [hsw backlight bisected] backlight is off after resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80773

--- Comment #20 from Ortwin Glück <odi at odi.ch> ---
Created attachment 108913
  --> https://bugs.freedesktop.org/attachment.cgi?id=108913&action=edit
debug output

This is the debug output of a complete cycle: power-on/suspend/resume/power-off
that demos the backlight problem.
Excerpt:

after resume backlight comes on quickly:
[   90.150434] [drm:intel_dp_complete_link_train] Channel EQ done. DP Training
successful
[   90.150584] [drm:intel_edp_backlight_on] 
[   90.150586] [drm:intel_panel_enable_backlight] pipe A
[   90.150591] [drm:intel_panel_actually_set_backlight] set backlight PWM =
2789

this is pm-utils writing 0, then 2789 to
/sys/class/backlight/intel_backlight/brightness:
[   90.235459] [drm:intel_backlight_device_update_status] updating
intel_backlight, brightness=2789/4648, bl_power=1, by pm-suspend
[   90.235468] [drm:intel_panel_actually_set_backlight] set backlight PWM =
2789

then something turns it off again:
[   90.235510] [drm:intel_edp_backlight_power] panel power control backlight
disable

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