edp backtrace spam on MacBookAir4,1

[Daniel Vetter]

On Thu, Jun 07, 2012 at 09:26:23AM +0200, Daniel Vetter wrote:
> 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

v3 is tested by our QA and hopefully works. I'll send it to Dave for
-fixes in a few days, attached below just in case. Please yell if this
doesn't fix your edp dmesg spam.

Thanks, Daniel
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