PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression)

[Nick Bowler]

Hi,

Testing out 4.3-rc2, first thing I notice is that the VGA output is
not working.  Specifically, the display is continuously powering on
and off -- at no point is any image visible on the screen (I am expecting
to see the console output).  The display connected to the HDMI output is
working fine.

Linux 4.2 did not suffer from this problem.

In dmesg I see the following messages, which I do not see on a working
kernel.  Full dmesg from 4.3-rc2 is attached (gzipped).

  [    0.115339] [drm:drm_calc_timestamping_constants] *ERROR* crtc
21: Can't calculate constants, dotclock = 0!
  [    0.117582] [drm:intel_opregion_init] *ERROR* No ACPI video bus found

This is an older machine with Intel G45 graphics.

Unfortunately bisection is proving difficult, because the commits it
wants me to test have a different problem: neither display comes up at
all (both remain in standby).  Partial results follow.

Thanks,
  Nick

  git bisect start 'drivers/gpu/drm/i915'
  # bad: [1f93e4a96c9109378204c147b3eec0d0e8100fde] Linux 4.3-rc2
  git bisect bad 1f93e4a96c9109378204c147b3eec0d0e8100fde
  # good: [64291f7db5bd8150a74ad2036f1037e6a0428df2] Linux 4.2
  git bisect good 64291f7db5bd8150a74ad2036f1037e6a0428df2
  # skip: [a7a6c498927ea42c9a3b26e0caa5c854a980d58c] drm/i915:
POSTING_READ() in intel_set_memory_cxsr()
  git bisect skip a7a6c498927ea42c9a3b26e0caa5c854a980d58c
  # skip: [031b698a77a70a6c394568034437b5486a44e868] drm/i915:
Unconditionally do fb tracking invalidate in set_domain
  git bisect skip 031b698a77a70a6c394568034437b5486a44e868
  # skip: [adeca76d8e2b34b5c739a36f4191aed63080da40] drm/i915:
Simplify i915_gem_execbuffer_retire_commands() parameters
  git bisect skip adeca76d8e2b34b5c739a36f4191aed63080da40
  # good: [369712e89404089fa559235bb1ee8fc40d976e6b] drm/i915: reduce
duplicate conditions in i9xx_hpd_irq_handler
  git bisect good 369712e89404089fa559235bb1ee8fc40d976e6b
  # skip: [6eb1a6817246f1a67de4d6959a84d09efead5329] drm/i915: Read wm
values from hardware at init on CHV
  git bisect skip 6eb1a6817246f1a67de4d6959a84d09efead5329
  # bad: [d14e7b6d1d8747826cb900db852351c550e00fdd] drm/i915: Check DP
link status on long hpd too
  git bisect bad d14e7b6d1d8747826cb900db852351c550e00fdd
  # skip: [fe36f55d4d4447679923fc74564786ae423ca4bd] drm/i915/gtt:
Cleanup page directory encoding
  git bisect skip fe36f55d4d4447679923fc74564786ae423ca4bd
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