on CI igt@kms_cursor_legacy@basic-flip-before-cursor-atomic failed on CI

https://intel-gfx-ci.01.org/CI/CI_DRM_2589/fi-skl-6770hq/igt@kms_cursor_legacy@basic-flip-before-cursor-atomic.html

dmesg:
https://intel-gfx-ci.01.org/CI/CI_DRM_2589/fi-skl-6770hq/dmesg-during.log

Out	
IGT-Version: 1.18-gb087257 (x86_64) (Linux: 4.11.0-CI-CI_DRM_2589+ x86_64)
Stack trace:
  #0 [__igt_fail_assert+0x101]
  #1 [basic_flip_cursor+0x695]
  #2 [<unknown>+0x695]
Subtest basic-flip-before-cursor-atomic: FAIL (0.386s)
Err	
(kms_cursor_legacy:9253) CRITICAL: Test assertion failure function basic_flip_cursor, file kms_cursor_legacy.c:669:
(kms_cursor_legacy:9253) CRITICAL: Failed assertion: get_vblank(display->drm_fd, pipe, 0) == vblank_start + 1
(kms_cursor_legacy:9253) CRITICAL: error: 20376 != 20375
Subtest basic-flip-before-cursor-atomic failed.
**** DEBUG ****
(kms_cursor_legacy:9253) DEBUG: Test requirement passed: found
(kms_cursor_legacy:9253) DEBUG: Test requirement passed: display->is_atomic
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: DP-1: set_pipe(A)
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: DP-1: Selecting pipe A
(kms_cursor_legacy:9253) igt-fb-DEBUG: igt_create_fb_with_bo_size(width=1920, height=1200, format=0x34325258, tiling=0x0, size=0)
(kms_cursor_legacy:9253) igt-fb-DEBUG: igt_create_fb_with_bo_size(handle=1, pitch=7680)
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: A.0: plane_set_fb(67)
(kms_cursor_legacy:9253) DEBUG: Test requirement passed: set_fb_on_crtc(display, pipe, &fb_info)
(kms_cursor_legacy:9253) igt-fb-DEBUG: igt_create_fb_with_bo_size(width=64, height=64, format=0x34325241, tiling=0x0, size=0)
(kms_cursor_legacy:9253) igt-fb-DEBUG: igt_create_fb_with_bo_size(handle=2, pitch=256)
(kms_cursor_legacy:9253) DEBUG: Test requirement passed: cursor
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: A.2: plane_set_fb(82)
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: commit {
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     A: Setting mode 1920x1200 from DP-1
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.0, fb 67
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     src = (0, 0) 1920 x 1200 dst = (0, 0) 1920 x 1200
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.2, fb 82
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     src = (0, 0) 64 x 64 dst = (0, 0) 64 x 64
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     B: Setting NULL mode
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.0, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.2, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     C: Setting NULL mode
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.0, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.2, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-1: preparing atomic, pipe: A
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-2: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     HDMI-A-1: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-3: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     HDMI-A-2: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: }
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: A.0: plane_set_fb(67)
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: commit {
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.0, fb 67
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     src = (0, 0) 1920 x 1200 dst = (0, 0) 1920 x 1200
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: A.2, fb 82
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.0, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: B.2, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.0, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.1, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     populating plane data: C.2, fb 0
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-1: preparing atomic, pipe: A
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-2: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     HDMI-A-1: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     DP-3: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display:     HDMI-A-2: preparing atomic, pipe: None
(kms_cursor_legacy:9253) igt-kms-DEBUG: display: }
(kms_cursor_legacy:9253) CRITICAL: Test assertion failure function basic_flip_cursor, file kms_cursor_legacy.c:669:
(kms_cursor_legacy:9253) CRITICAL: Failed assertion: get_vblank(display->drm_fd, pipe, 0) == vblank_start + 1
(kms_cursor_legacy:9253) CRITICAL: error: 20376 != 20375
****  END  ****