nouveau: failed to initialise sync

[Corentin Labbe]

Hello

Since some days on next, nouveau fail to load:
[    2.754087] nouveau 0000:02:00.0: vgaarb: deactivate vga console
[    2.761260] Console: switching to colour dummy device 80x25
[    2.766888] nouveau 0000:02:00.0: NVIDIA MCP77/MCP78 (0aa480a2)
[    2.783954] nouveau 0000:02:00.0: bios: version 62.77.2a.00.04
[    2.810122] nouveau 0000:02:00.0: fb: 256 MiB stolen system memory
[    3.484031] nouveau 0000:02:00.0: DRM: VRAM: 256 MiB
[    3.488993] nouveau 0000:02:00.0: DRM: GART: 1048576 MiB
[    3.494308] nouveau 0000:02:00.0: DRM: TMDS table version 2.0
[    3.500052] nouveau 0000:02:00.0: DRM: DCB version 4.0
[    3.505192] nouveau 0000:02:00.0: DRM: DCB outp 00: 01000300 0000001e
[    3.511632] nouveau 0000:02:00.0: DRM: DCB outp 01: 01011332 00020010
[    3.518074] nouveau 0000:02:00.0: DRM: DCB conn 00: 00000100
[    3.523728] nouveau 0000:02:00.0: DRM: DCB conn 01: 00001261
[    3.529455] nouveau 0000:02:00.0: DRM: failed to initialise sync subsystem, -28
[    3.545946] nouveau: probe of 0000:02:00.0 failed with error -28

I bisected it to:
git bisect start
# good: [62fb9874f5da54fdb243003b386128037319b219] Linux 5.13
git bisect good 62fb9874f5da54fdb243003b386128037319b219
# bad: [fb0ca446157a86b75502c1636b0d81e642fe6bf1] Add linux-next specific files for 20210701
git bisect bad fb0ca446157a86b75502c1636b0d81e642fe6bf1
# good: [f63c4fda987a19b1194cc45cb72fd5bf968d9d90] Merge remote-tracking branch 'rdma/for-next'
git bisect good f63c4fda987a19b1194cc45cb72fd5bf968d9d90
# bad: [49c8769be0b910d4134eba07cae5d9c71b861c4a] Merge remote-tracking branch 'drm/drm-next'
git bisect bad 49c8769be0b910d4134eba07cae5d9c71b861c4a
# good: [4e3db44a242a4e2afe33b59793898ecbb61d478e] Merge tag 'wireless-drivers-next-2021-06-25' of git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/wireless-drivers-next
git bisect good 4e3db44a242a4e2afe33b59793898ecbb61d478e
# bad: [5745d647d5563d3e9d32013ad4e5c629acff04d7] Merge tag 'amd-drm-next-5.14-2021-06-02' of https://gitlab.freedesktop.org/agd5f/linux into drm-next
git bisect bad 5745d647d5563d3e9d32013ad4e5c629acff04d7
# bad: [c99c4d0ca57c978dcc2a2f41ab8449684ea154cc] Merge tag 'amd-drm-next-5.14-2021-05-19' of https://gitlab.freedesktop.org/agd5f/linux into drm-next
git bisect bad c99c4d0ca57c978dcc2a2f41ab8449684ea154cc
# bad: [ae25ec2fc6c5a9e5767bf1922cd648501d0f914c] Merge tag 'drm-misc-next-2021-05-17' of git://anongit.freedesktop.org/drm/drm-misc into drm-next
git bisect bad ae25ec2fc6c5a9e5767bf1922cd648501d0f914c
# bad: [cac80e71cfb0b00202d743c6e90333c45ba77cc5] drm/vkms: rename cursor to plane on ops of planes composition
git bisect bad cac80e71cfb0b00202d743c6e90333c45ba77cc5
# good: [178bdba84c5f0ad14de384fc7f15fba0e272919d] drm/ttm/ttm_device: Demote kernel-doc abuses
git bisect good 178bdba84c5f0ad14de384fc7f15fba0e272919d
# bad: [3f3a6524f6065fd3d130515e012f63eac74d96da] drm/dp: Clarify DP AUX registration time
git bisect bad 3f3a6524f6065fd3d130515e012f63eac74d96da
# bad: [6dd7efc437611db16d432e0030f72d0c7e890127] drm/gud: cleanup coding style a bit
git bisect bad 6dd7efc437611db16d432e0030f72d0c7e890127
# bad: [13b29cc3a722c2c0bc9ab9f72f9047d55d08a2f9] drm/mxsfb: Don't select DRM_KMS_FB_HELPER
git bisect bad 13b29cc3a722c2c0bc9ab9f72f9047d55d08a2f9
# bad: [d02117f8efaa5fbc37437df1ae955a147a2a424a] drm/ttm: remove special handling for non GEM drivers
git bisect bad d02117f8efaa5fbc37437df1ae955a147a2a424a
# good: [13ea9aa1e7d891e950230e82f1dd2c84e5debcff] drm/ttm: fix error handling if no BO can be swapped out v4
git bisect good 13ea9aa1e7d891e950230e82f1dd2c84e5debcff
# first bad commit: [d02117f8efaa5fbc37437df1ae955a147a2a424a] drm/ttm: remove special handling for non GEM drivers

Reverting the patch permit to have nouveau works again.

Regards