Incomplete stable drm/ast backport - screen freeze on boot

[Keno Fischer]

When connected to a remote machine via the BMC KVM functionality,
I am experiencing screen freezes when attempting to install mantic
(lunar is fine). Upstream master is also fine. Bisecting the ubuntu
kernel branch, I found:

```
git bisect start
# status: waiting for both good and bad commits
# bad: [0eec6d2a63d86ac94dc8fa7c56820a0972ccbe1f] UBUNTU: Ubuntu-6.5.0-12.12
git bisect bad 0eec6d2a63d86ac94dc8fa7c56820a0972ccbe1f
# status: waiting for good commit(s), bad commit known
# good: [9ee3c53fe0c7d824a1de962e177da4336f5bea26] UBUNTU: Ubuntu-6.5.0-2.2
git bisect good 9ee3c53fe0c7d824a1de962e177da4336f5bea26
# good: [c344403b4a5fd6a41b4961079a7e68f5542c8fcb] UBUNTU: SAUCE: allows to enable Rust with modversions
git bisect good c344403b4a5fd6a41b4961079a7e68f5542c8fcb
# good: [890166a2bf6fde55c2e3b83baabed282391b5ece] watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check()
git bisect good 890166a2bf6fde55c2e3b83baabed282391b5ece
# bad: [80b1a5a85758d1140c74b84b0a24643fe20d756b] scsi: ufs: Fix residual handling
git bisect bad 80b1a5a85758d1140c74b84b0a24643fe20d756b
# bad: [33252ba0195ad945b9defd96ee177751e913f1aa] smackfs: Prevent underflow in smk_set_cipso()
git bisect bad 33252ba0195ad945b9defd96ee177751e913f1aa
# good: [81ab44acfe794705fe68c6b3256043c6a0a95749] arm64: dts: qcom: pm8350b: fix thermal zone name
git bisect good 81ab44acfe794705fe68c6b3256043c6a0a95749
# good: [119b834594e5151beaf06bdc80a98c61c87cda9a] arm64: dts: qcom: msm8996-gemini: fix touchscreen VIO supply
git bisect good 119b834594e5151beaf06bdc80a98c61c87cda9a
# good: [f46694216f1d5edcd9b9572cbf29b46661409789] arm64: dts: qcom: sm8150: Fix the I2C7 interrupt
git bisect good f46694216f1d5edcd9b9572cbf29b46661409789
# bad: [f30e95bc205987fe034babc2057790c273f360be] drm/msm/dpu: fix DSC 1.2 block lengths
git bisect bad f30e95bc205987fe034babc2057790c273f360be
# bad: [88895f3d6635ebfd7a9803211eaa0e40f7d9d163] drm/panel: simple: Add missing connector type and pixel format for AUO T215HVN01
git bisect bad 88895f3d6635ebfd7a9803211eaa0e40f7d9d163
# bad: [4b85b2ba439fc85d561775e98bdb218afc1b73cc] ARM: dts: BCM53573: Fix Tenda AC9 switch CPU port
git bisect bad 4b85b2ba439fc85d561775e98bdb218afc1b73cc
# bad: [916ae609a033cbb55661905d310ba2358b7621ea] drm/ast: report connection status on Display Port.
git bisect bad 916ae609a033cbb55661905d310ba2358b7621ea
# first bad commit: [916ae609a033cbb55661905d310ba2358b7621ea] drm/ast: report connection status on Display Port.
```

Which led to test the upstream 6.5 stable branch and found the issue
present there as well. I have submitted a report upstream, copied below,
but I was hoping to get a quick resolution in Ubuntu as well, since
it appears that the BMC KVM is currently unusable on any machines that
have mantic installed, which is a bit of a precarious situation, since
the BMC KVM is intended as recovery tool.

Upstream report (https://lists.freedesktop.org/archives/dri-devel/2023-November/430527.html):
```
The BMC on the machine in question is an ASpeed AST2600.
A quick bisect shows the problematic commit to be 2fb9667
("drm/ast: report connection status on Display Port.").
This is commit f81bb0ac upstream.

I believe the problem is that the previous commit in the series
e329cb5 ("drm/ast: Add BMC virtual connector")
was not backported to the stable branch.
As a consequence, it appears that the more accurate DP state detection
is causing the kernel to believe that no display is connected,
even when the BMC's virtual display is in fact in use.
A cherry-pick of e329cb5 onto the stable branch resolves the issue.
```

[Keno Fischer (keno-o)]

Just in case anybody else runs into this, an effective workaround is to set `modprobe.blacklist=ast` on the kernel command line.

[Brian Murray (brian-murray)]

Ubuntu 23.10 (Mantic Minotaur) has reached end of life, so this bug will not be fixed for that specific release.