Pageflip failure on SNB devices running 3.13.3

[Simon Farnsworth <simon.farnsworth@onelan.co.uk>]

Hello,

I'm seeing pageflips give up on me on SNB hardware - Celeron 847, i5-2400S - 
where the CRTC becomes unexpectedly busy and never recovers.

When I'm failed, I can see interrupts coming in (Interrupts received in 
/sys/kernel/debug/dri/0/i915_gem_interrupt increments), but the queued flip 
never happens:

 # cat /sys/kernel/debug/dri/0/i915_gem_pageflip 
Flip queued on pipe A (plane A)
Stall check enabled, 1 prepares
Old framebuffer gtt_offset 0x01354000
New framebuffer gtt_offset 0x0093c000
No flip due on pipe B (plane B)

 # cat /sys/kernel/debug/dri/0/i915_gem_interrupt 
North Display Interrupt enable:         8eb48585
North Display Interrupt identity:       00000000
North Display Interrupt mask:           734bfa7a
South Display Interrupt enable:         ffffffff
South Display Interrupt identity:       00000000
South Display Interrupt mask:           f114ffff
Graphics Interrupt enable:              00401001
Graphics Interrupt identity:            00000000
Graphics Interrupt mask:                ffffffff
Interrupts received: 1006958
Graphics Interrupt mask (render ring):  ffffffff
Current sequence (render ring): 1472838
Graphics Interrupt mask (bsd ring):     ffffffff
Current sequence (bsd ring): 1271460
Graphics Interrupt mask (blitter ring): ffffffff
Current sequence (blitter ring): 1472839

I'm running packages from Fedora 20:

# rpm -q mesa-libGL kernel xorg-x11-server-Xorg xorg-x11-drv-intel libva-
intel-driver libdrm
mesa-libGL-9.2.5-1.20131220.fc20.x86_64
kernel-3.13.3-201.fc20.x86_64
xorg-x11-server-Xorg-1.14.4-90.fc20.x86_64
xorg-x11-drv-intel-2.21.15-5.fc20.x86_64
libva-intel-driver-1.2.1-1.fc20.x86_64
libdrm-2.4.50-1.fc20.x86_64

I've put a dmesg from a failed system at http://90.155.96.198/sfarnsworth/flip-fail.txt - it's 11.3MB, so can't be attached. I've spotted the MCH_SSKPD 
message, but I also get the failures on systems that don't output that 
message.

Any ideas? Or should I file a bug?
-- 
Simon Farnsworth
Software Engineer
ONELAN Ltd
http://www.onelan.com