[SRU][J][PATCH 0/1] Black screen when booting 5.15.0-160 (on AMD Lucienne / Cezanne / Navi / Renoir / Rembrandt)

[Manuel Diewald]

BugLink: https://bugs.launchpad.net/bugs/2128729

SRU Justification:

[Impact]

The Ubuntu backport of e6a7df96facdc ("drm/amd/display: Fix MST Null Ptr
for RV") to fix CVE-2024-26700 does not consider that
compute_mst_dsc_configs_for_state() returns a boolean to
indicate success or failure in 5.15, while it returns an integer
in later kernel versions with 0 indicating success. This means
we need to flip the error condition when checking whether the
call succeeded when backporting this to 5.15 and older.
    
Currently, the error path is taken even though the call to
compute_mst_dsc_configs_for_state() succeeds which causes some systems
to have no video output or a black screen while the system is running.

This is causing loss of video output to screens on affected amdgpu
hardware.

[Fix]

Check the return value of compute_mst_dsc_configs_for_state() in
amdgpu_dm_atomic_check() correctly.

[Test Plan]

Without the fix, there will be no video output to the screen and the
following messages can be found in the kernel log if the kernel is
booted with drm.debug=0x2:

kernel: [drm:amdgpu_dm_atomic_check [amdgpu]] compute_mst_dsc_configs_for_state() failed
kernel: [drm:amdgpu_dm_atomic_check [amdgpu]] Atomic check failed with err: -22

With the fix applied, video output should return to normal and the
kernel warnings will disappear from the log.

[Where problems could occur]

Problems would be observed in odd behavior of the amdgpu driver,
particularly for hardware with DSC support.

Manuel Diewald (1):
  UBUNTU: SAUCE: drm/amd/display: Fix incorrect code path taken in
    amdgpu_dm_atomic_check()

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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2.34.1