[Intel-gfx] i915 and vbetool

[Holger Schurig]

Hi all,

I have various devices where I can control the backlight via "vbetool dpms
off" and "vbetool dpms on" (basically terminals with industrial
motherboards from Congatec or Advantech).

The context is some hardware test after manufacturing, so I'm running in
the text console. No X11 is (or has been) started.

So far this worked. But I have one device based on I5/Haswell (8086:0a16),
where vbetool doesn't work. I can turn backlight/dpms off, but not on
again. The backlight itself goes on again, but the screen is totally dark.
I also get dmesg output.

root:/sys# dmesg >/dev/null
root:/sys# vbetool dpms off
root:/sys# dmesg -c
[  325.704229] [drm:intel_uncore_check_errors [i915]] *ERROR* Unclaimed
register before interrupt
[  326.290205] [drm:intel_uncore_check_errors [i915]] *ERROR* Unclaimed
register before interrupt
root:/sys# vbetool dpms on
root:/sys# dmesg -c
[  340.408883] [drm:intel_uncore_check_errors [i915]] *ERROR* Unclaimed
register before interrupt
[  340.682288] [drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR*
uncleared fifo underrun on pipe A
[  340.682348] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU
pipe A FIFO underrun

At this point the backlight is on, but the screen still dark.

So, after a reboot I tried to save the state, using "vbetool vbestate save
>a". Then DPMS off, on again, and "vbetool vbestate restore <a". Despite
getting even more dmesg output from the two additional vbetool calls, I now
see a little but of the text. But it's greatly enlarged, probably the upper
left quarter of the former display now magnified over the whole screen.



vbetool is 1.1-3 from Debian Jessie.



Device (lspci -nn):

00:02.0 VGA compatible controller [0300]: Intel Corporation Haswell-ULT
Integrated Graphics Controller [8086:0a16] (rev 0b)

The other industrial board where vbetool worked correct for setting DPMS
state has this hardware:

00:02.0 VGA compatible controller [0300]: Intel Corporation N10 Family
Integrated Graphics Controller [8086:a011]



Some dmesg output from the non-working device that might be relevant:

[    0.221025] vgaarb: setting as boot device: PCI:0000:00:02.0
[    0.221099] vgaarb: device added:
PCI:0000:00:02.0,decodes=io+mem,owns=io+mem,locks=none
[    0.221168] vgaarb: loaded
[    0.221225] vgaarb: bridge control possible 0000:00:02.0
...
[    2.969865] [drm] Memory usable by graphics device = 2048M
[    2.969930] [drm] Replacing VGA console driver
[    2.970595] Console: switching to colour dummy device 80x25
[    2.976807] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[    2.976814] [drm] Driver supports precise vblank timestamp query.
[    2.976895] vgaarb: device changed decodes:
PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[    3.003257] fbcon: inteldrmfb (fb0) is primary device
[    3.005096] ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post:
no)
[    3.005312] input: Video Bus as
/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input17
[    3.005362] [drm] Initialized i915 1.6.0 20150731 for 0000:00:02.0 on
minor 0
[    4.092573] Console: switching to colour frame buffer device 128x48
[    4.096012] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device
...



I think I have to use vbetools for the backlight. All of those devices I
have /sys/class/backlight/intel_backlight/ as well, but that is a no-op, I
cannot turn off the backlight via it, neither by setting the pwm to 0 nor
by setting the bl_power.
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