I'm getting some weird results when using vblank_count on my Ivybridge machine across suspend/resume.
With glxgears running, I suspend the machine. At resume, I see vblank_count temporarily jump back by a fairly large amount (usually between 10000 and 20000 frames). After a short while, it recovers and jumps back to something that looks like it's back on track with values From before the suspend.
I thought at first that the value was just getting set back and left there, but after working around that kind of bug, I discovered that it only stayed on the wrong sequence for a short while (looks like about 20ms) and then jumps back to the previous sequence. I hacked up the vblank code to show where the errors occurred, and here's what I got (the logged MSC values are bogus, but the sequence of events is correct):
Vblank goes haywire here:
[ 30348.438] expect msc near 4294871473 got msc 4294860521 [ 30348.441] (II) intel(0): EDID vendor "APP", prod id 40178 [ 30348.442] (II) intel(0): Printing DDC gathered Modelines: [ 30348.442] (II) intel(0): Modeline "1366x768"x0.0 72.00 1366 1380 1436 1500 768 769 772 800 -hsync -vsync (48.0 kHz eP)
Vblank recovers here:
[ 30348.458] expect msc near 4294849570 got msc 4294860522