[0/3] drm/amd/display: fixes for kernel crashes since cursor overlay mode

Message

Melissa Wen Dec. 17, 2024, 8:45 p.m. UTC

Hi,

Some issues have been found by Cosmic users of AMD display since the
introduction of cursor overlay mode: page fault and divide errors
causing interface freezes. Both are 100% reproducible and affects
multiple HW versions.

Patch 1 addresses the page fault error by resolving the definition
mismatch around the number of surfaces supported by the hw, where two
different values (MAX_SURFACES and MAX_SURFACE_NUM) would be taken
through the DC surface updates flow. The regular flow take MAX_SURFACES
== 3 into account and commit_minimal_transition_state uses
MAX_SURFACE_NUM == 6. I noticed that Leo Li has proposed this change in
a previous discussion [1], so I added a Suggested-by tag.

Patch 2 expands the maximum number of surfaces to four, since it's
supported by the hw. Also, this amount accomodates current needs,
avoiding `dc_state_add_plane` complaints of not enough resource. Note
that it somehow reverts the change proposed by [2].

Related AMD issues:
- https://gitlab.freedesktop.org/drm/amd/-/issues/3693
- https://gitlab.freedesktop.org/drm/amd/-/issues/3594

Patch 3 fixes a kernel oops due to division by zero error by checking if
the destination scale size is zero, avoiding calculation and just
setting the out-scale size to zero, similar to what is  done by
drm_calc_scale(). Even though the missing check in dm_get_plane_scale()
wasn't introduced by cursor overlay mode, AFAIU the cursor mode
assessment happens before plane state checks, so
amdgpu_dm_plane_helper_check_state() can't prevent
dm_crtc_get_cursor_mode() taking an invisible plane into account.

Related AMD issue:
- https://gitlab.freedesktop.org/drm/amd/-/issues/3729

Other previous discussions can be found at:
- https://lore.kernel.org/amd-gfx/[e-mail]/
- https://lore.kernel.org/amd-gfx/[e-mail]/

Thanks in advance for any feedback.

Melissa

[1] https://lore.kernel.org/amd-gfx/[e-mail]/
[2] https://gitlab.freedesktop.org/agd5f/linux/-/commit/3cfd03b79425c

Melissa Wen (3):
  drm/amd/display: fix page fault due to max surface definition mismatch
  drm/amd/display: increase MAX_SURFACES to the value supported by hw
  drm/amd/display: fix divide error in DM plane scale calcs

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c       | 4 ++--
 drivers/gpu/drm/amd/display/dc/core/dc.c                | 2 +-
 drivers/gpu/drm/amd/display/dc/core/dc_state.c          | 8 ++++----
 drivers/gpu/drm/amd/display/dc/dc.h                     | 4 ++--
 drivers/gpu/drm/amd/display/dc/dc_stream.h              | 2 +-
 drivers/gpu/drm/amd/display/dc/dc_types.h               | 1 -
 drivers/gpu/drm/amd/display/dc/dml2/dml2_mall_phantom.c | 2 +-
 7 files changed, 11 insertions(+), 12 deletions(-)