Bug 103355

APL-shards CI_DRM_3277 igt@kms_cursor_legacy@cursor-vs-flip-atomic

(kms_cursor_legacy:5583) CRITICAL: Test assertion failure function cursor_vs_flip, file kms_cursor_legacy.c:1066:
(kms_cursor_legacy:5583) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:5583) CRITICAL: Last errno: 25, Inappropriate ioctl for device
(kms_cursor_legacy:5583) CRITICAL: completed 836 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-atomic failed.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3277/shard-apl6/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html

new subtest:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3324/shard-glkb1/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html

(kms_cursor_legacy:7212) CRITICAL: Test assertion failure function cursor_vs_flip, file kms_cursor_legacy.c:1066:
(kms_cursor_legacy:7212) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:7212) CRITICAL: Last errno: 25, Inappropriate ioctl for device
(kms_cursor_legacy:7212) CRITICAL: completed 2836 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-atomic-transitions failed.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3356/shard-glkb4/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html

(kms_cursor_legacy:13431) CRITICAL: Test assertion failure function cursor_vs_flip, file kms_cursor_legacy.c:1066:
(kms_cursor_legacy:13431) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:13431) CRITICAL: completed 1456 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-varying-size failed.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3356/shard-apl6/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html

(kms_cursor_legacy:4401) CRITICAL: Test assertion failure function cursor_vs_flip, file kms_cursor_legacy.c:1066:
(kms_cursor_legacy:4401) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:4401) CRITICAL: completed 819 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-varying-size failed.

https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_502/shard-apl4/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html

(kms_cursor_legacy:1786) CRITICAL: Test assertion failure function cursor_vs_flip, file kms_cursor_legacy.c:1066:
(kms_cursor_legacy:1786) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1786) CRITICAL: completed 880 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-legacy failed.

Since some of the links are dead above here are some more recent ones exposing the same issue:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3698/shard-apl2/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
https://intel-gfx-ci.01.org/tree/drm-tip/IGT_4177/shard-glkb2/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3705/shard-apl2/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3705/shard-glkb6/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html

Last seen:  CI_DRM_3754: 2018-02-12 / 280 runs ago

Now also on HSW: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3977/shard-hsw3/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html

(kms_cursor_legacy:1416) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1100:
(kms_cursor_legacy:1416) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1416) CRITICAL: completed 7404 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-varying-size failed.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_4025/shard-hsw3/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

(kms_cursor_legacy:2541) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1100:
(kms_cursor_legacy:2541) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:2541) CRITICAL: completed 7542 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-toggle failed.

https://intel-gfx-ci.01.org/tree/drm-tip/IGT_4417_full/shard-kbl4/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

(kms_cursor_legacy:1384) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1100:
(kms_cursor_legacy:1384) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1384) CRITICAL: completed 7581 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-toggle failed.

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_30/fi-kbl-7560u/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

(kms_cursor_legacy:1727) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1100:
(kms_cursor_legacy:1727) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1727) CRITICAL: completed 7105 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-toggle failed.

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_89/fi-bdw-5557u/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

(kms_cursor_legacy:1338) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1101:
(kms_cursor_legacy:1338) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1338) CRITICAL: completed 7240 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-toggle failed.

Also seen on ICL: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_5324/shard-iclb3/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html

Starting subtest: cursor-vs-flip-atomic-transitions-varying-size
(kms_cursor_legacy:5035) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1101:
(kms_cursor_legacy:5035) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:5035) CRITICAL: Last errno: 25, Inappropriate ioctl for device
(kms_cursor_legacy:5035) CRITICAL: completed 1222 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-atomic-transitions-varying-size failed.

More issues on ICL: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_5317/shard-iclb3/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html

Starting subtest: cursor-vs-flip-atomic-transitions-varying-size
(kms_cursor_legacy:4834) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1101:
(kms_cursor_legacy:4834) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:4834) CRITICAL: Last errno: 25, Inappropriate ioctl for device
(kms_cursor_legacy:4834) CRITICAL: completed 1260 cursor updated in a period of 30 flips, we expect to complete approximately 7680 updates, with the threshold set at 3840
Subtest cursor-vs-flip-atomic-transitions-varying-size failed.

Also seen on WHL and SKL:

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_172/fi-skl-6770hq/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_172/fi-skl-6770hq/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_171/fi-whl-u/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html

https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_171/fi-whl-u/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html

Starting subtest: cursor-vs-flip-atomic-transitions
(kms_cursor_legacy:1344) CRITICAL: Test assertion failure function cursor_vs_flip, file ../tests/kms_cursor_legacy.c:1101:
(kms_cursor_legacy:1344) CRITICAL: Failed assertion: shared[0] > vrefresh*target / 2
(kms_cursor_legacy:1344) CRITICAL: Last errno: 25, Inappropriate ioctl for device
(kms_cursor_legacy:1344) CRITICAL: completed 1784 cursor updated in a period of 30 flips, we expect to complete approximately 15360 updates, with the threshold set at 7680
Subtest cursor-vs-flip-atomic-transitions failed.

A CI Bug Log filter associated to this bug has been updated:

{- HSW APL SKL KBL GLK WHL ICL: kms_cursor_legacy@cursor-vs-flip.* - Failed assertion: shared[0] > vrefresh*target / 2 -}
{+ GDG HSW APL SKL KBL GLK WHL ICL: kms_cursor_legacy@cursor-vs-flip.* - Failed assertion: shared[0] > vrefresh*target / 2 +}

New failures caught by the filter:

* https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_176/fi-gdg-551/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

Updating the platforms, and assigning Anusha since she started investigating this. Please update this bug with your progress :)

The test is checking how many cursor updates we can fit between vblanks, and treating that as a baseline. Then it does 30 flips and checks whether we fit expected (num_of_flips * baseline / 8) amount of cursor updates. The check is done 50 times.

We fails this check but yet the cursor refresh rate for each failure is well above 1k (per 30 flips) and there are really no sense in having mouses with refresh rates higher than 1kHz.

The customer impact is low.

The test needs some rethinking and possibly updated pass criteria.

(In reply to Arek Hiler from comment #18)
> The test is checking how many cursor updates we can fit between vblanks, and
> treating that as a baseline. Then it does 30 flips and checks whether we fit
> expected (num_of_flips * baseline / 8) amount of cursor updates. The check
> is done 50 times.
> 
> We fails this check but yet the cursor refresh rate for each failure is well
> above 1k (per 30 flips) and there are really no sense in having mouses with
> refresh rates higher than 1kHz.
> 
> The customer impact is low.
> 
> The test needs some rethinking and possibly updated pass criteria.

Anusha, please update the test to clip the wanted refresh rate to 1kHz, anything above above is useless and just adds noise.

(In reply to Martin Peres from comment #19)
> (In reply to Arek Hiler from comment #18)
> > The test is checking how many cursor updates we can fit between vblanks, and
> > treating that as a baseline. Then it does 30 flips and checks whether we fit
> > expected (num_of_flips * baseline / 8) amount of cursor updates. The check
> > is done 50 times.
> > 
> > We fails this check but yet the cursor refresh rate for each failure is well
> > above 1k (per 30 flips) and there are really no sense in having mouses with
> > refresh rates higher than 1kHz.
> > 
> > The customer impact is low.
> > 
> > The test needs some rethinking and possibly updated pass criteria.
> 
> Anusha, please update the test to clip the wanted refresh rate to 1kHz,
> anything above above is useless and just adds noise.

I dont think that will work. The test checks that a certain amount (targeteted amount) of cursor updates happens between vblanks and that flip do not affect vblank counter. The subtest already sets the targetted cursor updates to a pretty low value, despite that the test fails.  We need to understand -
1. how the flips are affecting the vblanks
2. why particularly in ICL we are not able to do that many number of cursor updates. (that is assuming this test was passing on non ICL systems). I plan on seeing the behaviour on my KBL system.

Also, just out of curiosity I did change the target value to see if at any point the test passes. it doesnt. Regardless of how less we set the cursor update, we fail to achieve that in the given interval.

(In reply to anusha from comment #20)
> I dont think that will work. The test checks that a certain amount
> (targeteted amount) of cursor updates happens between vblanks and that flip
> do not affect vblank counter. The subtest already sets the targetted cursor
> updates to a pretty low value, despite that the test fails.  We need to
> understand -
> 1. how the flips are affecting the vblanks
> 2. why particularly in ICL we are not able to do that many number of cursor
> updates. (that is assuming this test was passing on non ICL systems). I plan
> on seeing the behaviour on my KBL system.
> 
> Also, just out of curiosity I did change the target value to see if at any
> point the test passes. it doesnt. Regardless of how less we set the cursor
> update, we fail to achieve that in the given interval.

Hey,

Just to be sure that I understand the test correctly:
1. we fork and do DRM_IOCTL_MODE_CURSOR in a "busy" loop
2. we wait for 30 flips (vrefresh/2, vrefresh=60)
3. we check how many MODE_CURSOR have succeeded
4. we compare the number of times we managed to call the IOCTL vs our target*30

Currently the "target" comes from get_cursor_updates_per_vblank() which from the number of MODE_CURSOR ioctl we manage to squeeze in between two vblanks divided by 8.

We have seen a lot of failures where the target was not hit, but still all of them managed to do about 1.5k cursor updates in that time, which means about 3kHz cursor update rate, which is plenty.

That would mean if we have over 500 updates in that 30 frame window (0.5s) we would hit the 1kHz requirement.

What am I missing in this reasoning?

(In reply to Arek Hiler from comment #21)
> (In reply to anusha from comment #20)
> > I dont think that will work. The test checks that a certain amount
> > (targeteted amount) of cursor updates happens between vblanks and that flip
> > do not affect vblank counter. The subtest already sets the targetted cursor
> > updates to a pretty low value, despite that the test fails.  We need to
> > understand -
> > 1. how the flips are affecting the vblanks
> > 2. why particularly in ICL we are not able to do that many number of cursor
> > updates. (that is assuming this test was passing on non ICL systems). I plan
> > on seeing the behaviour on my KBL system.
> > 
> > Also, just out of curiosity I did change the target value to see if at any
> > point the test passes. it doesnt. Regardless of how less we set the cursor
> > update, we fail to achieve that in the given interval.
> 
> Hey,
> 
> Just to be sure that I understand the test correctly:
> 1. we fork and do DRM_IOCTL_MODE_CURSOR in a "busy" loop
> 2. we wait for 30 flips (vrefresh/2, vrefresh=60)
> 3. we check how many MODE_CURSOR have succeeded
> 4. we compare the number of times we managed to call the IOCTL vs our
> target*30
> 
> Currently the "target" comes from get_cursor_updates_per_vblank() which from
> the number of MODE_CURSOR ioctl we manage to squeeze in between two vblanks
> divided by 8.
> 
> We have seen a lot of failures where the target was not hit, but still all
> of them managed to do about 1.5k cursor updates in that time, which means
> about 3kHz cursor update rate, which is plenty.
> 
> That would mean if we have over 500 updates in that 30 frame window (0.5s)
> we would hit the 1kHz requirement.
> 
> What am I missing in this reasoning?

Yes. that is how I have understood it too. In the D stepping that I am using, we are  doing only about 1350 updates max. I tried to play around with reducing the threshold just to see at what point the test passes and the lesser we reduce the  threshold value to, the lesser updates we are doing. Which is very weird....

(In reply to anusha from comment #22)
> I tried to play around with reducing the threshold just to see at
> what point the test passes and the lesser we reduce the threshold
> value to, the lesser updates we are doing. Which is very weird....

Interesting. 'target' does not play any role in the test other than
serving as the baseline for comparison at the very end of an iteration.

The only thing that comes to my mind is that cursor gets progressively
slower. Can you check that, as I don't have ICL at hands?

We do nloops=50 of iterations for cursor-vs-flip. You can turn the
igt_assert_f() to an igt_debug() and see how the shared[0], which
has the number of performed updates, changes over the course
of execution.

Thanks!

https://patchwork.freedesktop.org/series/59577/

to get some more data on passes and fails

The CI Bug Log issue associated to this bug has been updated.

### New filters associated

* GDG HSW APL SKL KBL GLK WHL ICL: kms_cursor_legacy@cursor-vs-flip.* - Failed to meet cursor update expectations in \d+ out of \d+ iterations
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl1/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl3/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl4/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl6/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl7/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-apl8/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk2/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk2/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk3/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk3/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk4/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-glk6/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw5/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw5/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw5/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw7/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw7/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-hsw8/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb1/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb1/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb3/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb4/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb6/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-iclb7/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl1/igt@kms_cursor_legacy@cursor-vs-flip-atomic.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl2/igt@kms_cursor_legacy@cursor-vs-flip-legacy.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl3/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl4/igt@kms_cursor_legacy@cursor-vs-flip-varying-size.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl6/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions.html
  - https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_2865/shard-kbl7/igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size.html

I have just pushed the patch and updated all the filters. In a week or two we should have enough data to make a decision on the test's fate.

A CI Bug Log filter associated to this bug has been updated:

{- GDG HSW APL SKL KBL GLK WHL ICL: kms_cursor_legacy@cursor-vs-flip.* - Failed to meet cursor update expectations in \d+ out of \d+ iterations -}
{+ GDG BYT HSW APL SKL KBL GLK WHL ICL: kms_cursor_legacy@cursor-vs-flip.* - Failed to meet cursor update expectations in \d+ out of \d+ iterations +}

New failures caught by the filter:

  * https://intel-gfx-ci.01.org/tree/drm-tip/drmtip_292/fi-byt-n2820/igt@kms_cursor_legacy@cursor-vs-flip-toggle.html

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

You can subscribe and participate further through the new bug through this link to our GitLab instance: https://gitlab.freedesktop.org/drm/intel/issues/57.