Revert "drm/amd/display: Allocate DCN32/1 dmub memory to GTT"

After commit a637a140ab860310 ("drm/amd/display: Allocate DCN32/1 dmub
memory to GTT"), a machine with a Radeon RX 7900 shows random garbage on
the screen. It reproduces sporadically, but at times it is so bad the
machine is more or less unusable.

The garbage is always horizontal bars extending across the entire
screen, always approximately 200 pixels tall on a 3840x2160 screen,
for what looks like a single frame. The bars are mostly black, but will
sometimes exhibit striping and periodic artifacts which smell like
non-framebuffer data is being rendered to the screen.

It took some patience on the "good" side, but I was able to nail it down
to commit a637a140ab860310818a14fb4d37e39e51a06be4 with this bisect:

  bad: [cee9395acd8043be0644b25c34bfa86623f2b935] Linux 7.3-rc1
  good: [8d3ae59288f1e7d58d76558a6ee96d533bc5019f] Linux 7.2
  good: [55ab7e14222e5f0b0fd9f7711ca391d2924b35e3] Merge tag 'for-7.3/block-20260819' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux
  bad: [df51bdc5e80dae43cab81f6cc641e98638303c88] Merge tag 'mtd/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux
  bad: [29daacacf4cd84e6917f09de6a99fb170071c14c] Merge tag 'drm-rust-next-2026-08-08' of https://gitlab.freedesktop.org/drm/rust/kernel into drm-next
  good: [fff648aec5e2790d117a0ec5c849a284d9d33d70] drm/amdgpu: include amdgpu_video_codecs.h only where needed
  bad: [336e0cd576817ac64a4b394ca2b3680029f3e37f] Revert "drm/amdgpu: fix aperture mapping leak"
  bad: [789f7486a384ca58b9d7a76abba5efa0e80e8dab] drm/amd/display: Test plane colorop helper walkers
  good: [e0e426f10ad653c5e9dd33fb4a76d55f06101992] drm/amd/display: Test helper_check_state rejects
  bad: [982b2a43682b55e7d9800000f2592832ff2865ba] drm/amdgpu: Fix IP block NULL check during soft reset
  bad: [9102b39fa924dcc3dc75a3137bfa9633c40b88c0] drm/amdgpu/userq: fix indefinite fence wait during GPU reset
  bad: [b23470a026afe64de5c1df4ad181587b49c22923] drm/amd/display: Exit LS for ISHARP before coefficient write
  bad: [f02b2e47355e9d381a7f34acc997e1c47879ca21] drm/amd/display: Add KUnit test for wb jobs
  bad: [c6a13d145cc811b19c8a0620f25868cf7d5700c0] drm/amd/display: remove unused dcn42 socbb values
  good: [1d8327353de6f1f34063840f362c208c84064f54] drm/amd/display: Fix VABC Init and OLED Support
  bad: [a637a140ab860310818a14fb4d37e39e51a06be4] drm/amd/display: Allocate DCN32/1 dmub memory to GTT
  first 'bad' commit: [a637a140ab860310818a14fb4d37e39e51a06be4] drm/amd/display: Allocate DCN32/1 dmub memory to GTT

Sure enough, reverting a637a140ab860310818a14fb4d37e39e51a06be4 on top
of v7.3 completely and totally eliminates the problem for me.

Mikhail has separately reported this regression:

  https://lore.kernel.org/all/20260829010525.29935-1-mikhail.v.gavrilov@gmail.com/

...but it seems to be much more consistent for me than for Mikhail, it's
never taken more than 30 minutes even when the machine is completely
idle. I've also never been able to reproduce any artifact one single
time without commit a637a140, despite a lot of effort.

I'm not sure reverting this is the right way forward, since presumably
this would re-regress the timing issue Fangzhi alluded to in the
original commit. But nobody has proposed anything concrete yet... so
let's start the discussion here.

I'm happy to help test other better ideas as well :)

Fixes: a637a140ab86 ("drm/amd/display: Allocate DCN32/1 dmub memory to GTT")
Closes: https://lore.kernel.org/all/20260829010525.29935-1-mikhail.v.gavrilov@gmail.com/
Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5714
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 899489d2e2aa854cf5e933677d6561dfcbb94529)
Cc: stable@vger.kernel.org

0 files changed, 0 insertions, 0 deletions