edp backtrace spam on MacBookAir4,1

[Daniel Vetter]

On Thu, Jun 07, 2012 at 09:21:20AM +0200, Daniel Vetter wrote:
> On Wed, May 30, 2012 at 08:39:13AM -0700, Linus Torvalds wrote:
> > 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.
> 
> Meh, I've been totally blind. Note to self: Next time around actually look
> at the backtrace. And I dunno how that escaped our dear QA that long ...

Even more meh, this patch might actually work a bit better.

/me doesn't have an edp panel to test this

-Daniel
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