edp backtrace spam on MacBookAir4,1

[Linus Torvalds]

On Wed, May 30, 2012 at 1:27 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>
> Ok, Chris couldn't reproduce this on his mba. Can you please boot with
> drm.debug=0xe, reproduce the noise and then attach the full dmesg?

Hmm. Now *I* can't reproduce it either.

I have updated my system in the meantime, so maybe this is related to
that. However, I suspect it's more likely that it's some race
condition, because when I got it, I got a *lot* of it, but they were
all very tightly bunched together:

 [ 1588.996413] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1588.996650] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.000983] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.001225] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.005975] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.006218] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.010980] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.011224] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.015976] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.016211] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.020986] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()
 [ 1589.021232] WARNING: at drivers/gpu/drm/i915/intel_dp.c:350
intel_dp_check_edp+0x5d/0xb0()

ie that's 12 of those warnings (each of them with that huge backtrace
etc), but they are all within 0.03 seconds of each other. So I suspect
it needs to hit some particular timing window, and I was just
(un)lucky.

Because when I try it now with DRM debugging, I can't hit it. And just
to make sure, I re-did the test without debugging too (in case the
debugging would have changed timing), but can't reproduce it that way
either.

                             Linus