Created attachment 110381 [details]
dmesg

==System Environment==
--------------------------
Regression: not sure

Non-working platforms: BDW

Libdrm:		(master)libdrm-2.4.58-19-gf99522e678dbbaffeca9462a8edcbe900574dc12
Mesa:		(master)7b0067d23a6f64cf83c42e7f11b2cd4100c569fe
Xserver:	(master)xorg-server-1.16.99.901-21-g4b0d0df34f10a88c10cb23dd50087b59f5c4fece
Xf86_video_intel:(master)2.99.916-165-g9c2c485df9fd39ae36779f765a892e36835a8001
Libva:		(master)c095cc6cf08523cd0dffcfe5ac4bce9122527f22
Libva_intel_driver:(master)edbb8cdada09cd116103e68f942b0889fd767391

==kernel==
--------------------------
drm-intel-nightly/691817ae2a8f37cb1df33f21a6dd1c15a8832693
drm-intel-next-queued/5c8437fa462d45f5a6ae1020d340f6c8e6763df6
drm-intel-fixes/009d0431c3914de64666bec0d350e54fdd59df6a

==Bug detailed description==
-----------------------------
It causes "WARNING: CPU: 0 PID: 4925 at drivers/gpu/drm/i915/intel_uncore.c:726 hsw_unclaimed_reg_debug.isra.12+0x62/0x72 [i915]()".

Test on latest drm-intel-nightly, drm-intel-next-queued and drm-intel-fixes kernel, they all have this issue. Test on earlier kernel(2014_10_23/drm-intel-next-queued/1577c3c641970550bf9c4038f152e33c58428045), it also has this issue.

output:
root@x-bdw05:/GFX/Test/Piglit/piglit# bin/glx-oml-sync-control-timing -divisor 1
libGL: OpenDriver: trying /opt/X11R7/lib/dri/tls/i965_dri.so
libGL: OpenDriver: trying /opt/X11R7/lib/dri/i965_dri.so
libGL: Error in /etc/drirc line 1, column 0: no element found.
libGL: Error in /root/.drirc line 1, column 0: no element found.
libGL: Error in /etc/drirc line 1, column 0: no element found.
libGL: Error in /root/.drirc line 1, column 0: no element found.
PIGLIT: {"result": "pass" }
root@x-bdw05:/GFX/Test/Piglit/piglit# bin/glx-oml-sync-control-timing -divisor 1
libGL: OpenDriver: trying /opt/X11R7/lib/dri/tls/i965_dri.so
libGL: OpenDriver: trying /opt/X11R7/lib/dri/i965_dri.so
libGL: Error in /etc/drirc line 1, column 0: no element found.
libGL: Error in /root/.drirc line 1, column 0: no element found.
libGL: Error in /etc/drirc line 1, column 0: no element found.
libGL: Error in /root/.drirc line 1, column 0: no element found.
iteration 0 woke up 1 MSCs later than expected
PIGLIT: {"result": "warn" }

[   85.973496] ------------[ cut here ]------------
[   85.973516] WARNING: CPU: 0 PID: 4925 at drivers/gpu/drm/i915/intel_uncore.c:726 hsw_unclaimed_reg_debug.isra.12+0x62/0x72 [i915]()
[   85.973519] Unclaimed register detected before writing to register 0x44404
[   85.973519] Modules linked in: dm_mod iTCO_wdt iTCO_vendor_support ppdev snd_hda_codec_hdmi pcspkr snd_hda_intel snd_hda_controller i2c_i801 snd_hda_codec snd_hwdep lpc_ich snd_pcm mfd_core snd_timer snd soundcore battery parport_pc parport ac acpi_cpufreq i915 button video drm_kms_helper drm cfbfillrect cfbimgblt cfbcopyarea
[   85.973536] CPU: 0 PID: 4925 Comm: X Not tainted 3.18.0-rc7_drm-intel-nightly_691817_20141202+ #2170
[   85.973537]  0000000000000000 0000000000000009 ffffffff8178d622 ffff8800022efbe8
[   85.973540]  ffffffff8103a8cc ffff880002cd3bc0 ffffffffa00c0974 000000000000003f
[   85.973542]  ffff880002cd0060 0000000000044404 0000000000044404 000000006ffff8ee
[   85.973544] Call Trace:
[   85.973550]  [<ffffffff8178d622>] ? dump_stack+0x41/0x51
[   85.973554]  [<ffffffff8103a8cc>] ? warn_slowpath_common+0x78/0x90
[   85.973565]  [<ffffffffa00c0974>] ? hsw_unclaimed_reg_debug.isra.12+0x62/0x72 [i915]
[   85.973568]  [<ffffffff8103a97c>] ? warn_slowpath_fmt+0x45/0x4a
[   85.973578]  [<ffffffffa00c0974>] ? hsw_unclaimed_reg_debug.isra.12+0x62/0x72 [i915]
[   85.973587]  [<ffffffffa00c135d>] ? gen8_write32+0x8e/0x11a [i915]
[   85.973597]  [<ffffffffa00ab338>] ? gen8_enable_vblank+0x5a/0x85 [i915]
[   85.973603]  [<ffffffffa0010ecc>] ? drm_vblank_enable+0x51/0xa7 [drm]
[   85.973609]  [<ffffffffa001124b>] ? drm_vblank_get+0x46/0xa6 [drm]
[   85.973615]  [<ffffffffa00123b1>] ? drm_wait_vblank+0x8f/0x4c6 [drm]
[   85.973620]  [<ffffffffa0010738>] ? drm_ioctl+0x279/0x3bc [drm]
[   85.973626]  [<ffffffffa0012322>] ? drm_modeset_ctl+0x49/0x49 [drm]
[   85.973629]  [<ffffffff8107b426>] ? enqueue_hrtimer+0x36/0x6d
[   85.973631]  [<ffffffff8107bb1f>] ? __hrtimer_start_range_ns+0x276/0x29f
[   85.973634]  [<ffffffff8111e6e3>] ? do_vfs_ioctl+0x3ec/0x435
[   85.973637]  [<ffffffff8111e775>] ? SyS_ioctl+0x49/0x78
[   85.973640]  [<ffffffff81792cd2>] ? system_call_fastpath+0x12/0x17
[   85.973641] ---[ end trace 8075263230200184 ]---
[   85.975191] ------------[ cut here ]------------

Reproduce steps:
-------------------------
1. xinit&
2. ./bin/glx-oml-sync-control-timing -divisor 1 -auto