[Intel-gfx] [REGRESSION] i915: No HDMI output with 4.4

[Oleksandr Natalenko]

Hi.

With Linux 4.4 external HDMI-attached monitor in not discovered by i915 
driver. Here is boot log related to drm and i915 for Linux 4.4/4.4.1 
kernel:

===
kernel: [drm] Initialized drm 1.1.0 20060810
kernel: [drm] Memory usable by graphics device = 2048M
kernel: [drm] Replacing VGA console driver
kernel: [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
kernel: [drm] Driver supports precise vblank timestamp query.
kernel: [drm] Initialized i915 1.6.0 20151010 for 0000:00:02.0 on minor 
0
kernel: i915 0000:00:02.0: No connectors reported connected with modes
kernel: [drm] Cannot find any crtc or sizes - going 1024x768
kernel: i915 0000:00:02.0: fb0: inteldrmfb frame buffer device
===

i915 is unable to find any connectors. Reattaching HDMI cable does not 
help. Note, we are talking about in-kernel i915 drm with no X involved 
(launching X does not change anything, though).

Linux 4.3 worked OK. Here is boot log for 4.3 kernel:

===
kernel: [drm] Initialized drm 1.1.0 20060810
kernel: [drm] Memory usable by graphics device = 2048M
kernel: [drm] Replacing VGA console driver
kernel: [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
kernel: [drm] Driver supports precise vblank timestamp query.
kernel: [drm] Initialized i915 1.6.0 20150731 for 0000:00:02.0 on minor 
0
kernel: [drm:intel_set_pch_fifo_underrun_reporting [i915]] *ERROR* 
uncleared pch fifo underrun on pch transcoder A
kernel: [drm:intel_pch_fifo_underrun_irq_handler [i915]] *ERROR* PCH 
transcoder A FIFO underrun
kernel: i915 0000:00:02.0: fb0: inteldrmfb frame buffer device
===

Hardware:

===
[~]$ lscpu | grep "Model name"
Model name:            Intel(R) Pentium(R) CPU G2020 @ 2.90GHz

[~]$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v2/3rd 
Gen Core processor Graphics Controller (rev 09)
===

and xrandr output (with 4.3 kernel):

===
[~]$ xrandr --listproviders
Providers: number : 1
Provider 0: id: 0x47 cap: 0xb, Source Output, Sink Output, Sink Offload 
crtcs: 4 outputs: 4 associated providers: 0 name:Intel

[~]$ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected primary 1920x1080+0+0 (normal left inverted right x axis 
y axis) 510mm x 290mm
    1920x1080     60.00*+  50.00    59.94
    1920x1080i    60.00    50.00    59.94
    1680x1050     59.88
    1400x1050     59.95
    1600x900      60.00
    1280x1024     60.02
    1440x900      59.90
    1280x800      59.91
    1152x864      59.97
    1280x720      60.00    50.00    59.94
    1024x768      60.00
    800x600       60.32
    720x576       50.00
    720x480       60.00    59.94
    640x480       60.00    59.94
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
===

Ideas?