Is this that known? Afaik we only see it when enabing atomic modesetting for byt/bsw.

Hi, Yes, known when that will be enables. Was discussing with Ville that we could make bug and then enable so that no flickering on results. 

Always those tests fail on our CI BYT

So this is making but that we know to fail and we have not been able to changes that help on that spesific BYT device under CI.

Passes now on CI:
https://patchwork.freedesktop.org/series/20634/ but still 2 tests fails:
Test kms_cursor_legacy:
        Subgroup basic-flip-after-cursor-varying-size:
                pass       -> FAIL       (fi-byt-n2820) fdo#100415
        Subgroup basic-flip-before-cursor-varying-size:
                pass       -> FAIL       (fi-byt-n2820) fdo#100415

Assigning to Ville to make suggestions here.

See error:
Out	
IGT-Version: 1.18-gc774395 (x86_64) (Linux: 4.11.0-rc5-CI-Patchwork_4398+ x86_64)
Test requirement not met in function __real_main1388, file kms_cursor_legacy.c:1409:
Test requirement: !(n >= display.n_pipes)
Stack trace:
  #0 [__igt_fail_assert+0x101]
  #1 [basic_flip_cursor+0x608]
  #2 [<unknown>+0x608]
Subtest basic-flip-after-cursor-varying-size: FAIL (0.223s)
Err	
(kms_cursor_legacy:9923) CRITICAL: Test assertion failure function basic_flip_cursor, file kms_cursor_legacy.c:611:
(kms_cursor_legacy:9923) CRITICAL: Failed assertion: get_vblank(display->drm_fd, pipe, 0) == vblank_start
(kms_cursor_legacy:9923) CRITICAL: error: 24534 != 24533
Subtest basic-flip-after-cursor-varying-size failed.
**** DEBUG ****
(kms_cursor_legacy:9923) DEBUG: Test requirement passed: found
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: HDMI-A-1: set_pipe(A)
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: HDMI-A-1: Selecting pipe A
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(width=1600, height=900, format=0x34325258, tiling=0x0, size=0)
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(handle=1, pitch=6400)
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: A.0: plane_set_fb(70)
(kms_cursor_legacy:9923) DEBUG: Test requirement passed: set_fb_on_crtc(display, pipe, &fb_info)
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(width=64, height=64, format=0x34325241, tiling=0x0, size=0)
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(handle=2, pitch=256)
(kms_cursor_legacy:9923) DEBUG: Test requirement passed: cursor
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: A.3: plane_set_fb(71)
(kms_cursor_legacy:9923) DEBUG: Test requirement passed: !(width <= 64 && height <= 64)
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(width=256, height=256, format=0x34325241, tiling=0x0, size=0)
(kms_cursor_legacy:9923) igt-fb-DEBUG: igt_create_fb_with_bo_size(handle=3, pitch=1024)
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: commit {
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     A: Setting mode 1600x900 from HDMI-A-1
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: A.0, fb 70
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     src = (0, 0) 1600 x 900 dst = (0, 0) 1600 x 900
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: A.1, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: A.2, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: A.3, fb 71
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     src = (0, 0) 64 x 64 dst = (0, 0) 64 x 64
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     B: Setting NULL mode
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: B.0, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: B.1, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: B.2, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     populating plane data: B.3, fb 0
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     DP-1: preparing atomic, pipe: None
(kms_cursor_legacy:9923) igt-kms-DEBUG: display:     HDMI-A-1: preparing atomic, pipe: A
(kms_cursor_legacy:9923) igt-kms-DEBUG: display: }
(kms_cursor_legacy:9923) CRITICAL: Test assertion failure function basic_flip_cursor, file kms_cursor_legacy.c:611:
(kms_cursor_legacy:9923) CRITICAL: Failed assertion: get_vblank(display->drm_fd, pipe, 0) == vblank_start
(kms_cursor_legacy:9923) CRITICAL: error: 24534 != 24533
****  END  ****

With decisions made that cpumax=2 helps fixing 2 last issues.
And plane optimizations done by Ville.

Just to be clear, you are not suggesting that maxcpu=2 is a fix for this?

Well at least those two last cases 
est kms_cursor_legacy:
        Subgroup basic-flip-after-cursor-varying-size:
        Subgroup basic-flip-before-cursor-varying-size:

that was left after Ville's fix was fixed by that change. Ofcourse eventually we need to fix somehow on driver side I guess.