[PATCH 0/2] drm/amd/display: increase MAX_SURFACES in line with planes and streams

[Melissa Wen]

Hi!

AFAIU, the driver is defining two different max number of surfaces:
MAX_SURFACES (dc.h) and MAX_SURFACE_NUM (dc_types.h) Many years ago,
MAX_SURFACES was set 3 just to prevent a stack size warning as in
091a97e542cf ("drm/amd/display: Fix warning. Set MAX_SURFACES to 3")[1].
But according to commit 3cfd03b79425 ("update max streams per
surface")[2], from 2023, six is the real max number of surfaces
supported by any asics and the warning that motivated [1] seems not
valid anymore.

This mismatch looks a bit problematic per se, and I wonder if we should
start using only one definition (MAX_SURFACES or MAX_SURFACE_NUM) in the
whole driver.

Also, with MAX_PLANES and MAX_STREAMS both set as 6, there are some
driver with `max_slave_planes = 2` and so the maximum of 3 surfaces can
cause an array-index-out-of-bonds, as reported by [3] and pointed out in
the second patch of this series (MAX_SURFACES < plane_count).

I suppose that this blew up after 1d0c9ded4519 ("Introduce overlay
cursor mode") [4], since it uses one more DCN plane for cursor overlay
mode.

So, the first patch just update MAX_SURFACES to 6 and the second add
some debug prints to warn when changes on these values might cause
array-index-out-of-bounds.

Let me know your thoughts.

Thanks,

Melissa

[1] https://gitlab.freedesktop.org/agd5f/linux/-/commit/091a97e542cf
[2] https://gitlab.freedesktop.org/agd5f/linux/-/commit/3cfd03b79425
[3] https://gitlab.freedesktop.org/drm/amd/-/issues/3594
[4] https://lore.kernel.org/amd-gfx/20240315170959.165505-2-sunpeng.li@amd.com/

Melissa Wen (2):
  drm/amd/display: increase max surfaces in line with planes and streams
  drm/amd/display: add warnings for MAX_SURFACES mismatch

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 20 +++++++++++++++++++
 drivers/gpu/drm/amd/display/dc/dc.h           |  2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)

-- 
2.45.2