On Thu, Sep 24, 2015 at 05:22:09PM -0400, Nick Bowler wrote:
> 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