drm/amdgpu: serialize vblank counter reads against GPU reset

The vblank counter callback reads display registers and scanout
position without holding reset_domain->sem. During GPU recovery,
display commit work can call the callback while reset owns the
semaphore for writing. The hardware access then triggers the
lockdep_assert_held() in amdgpu_device_skip_hw_access() and sets
TAINT_WARN when lockdep is enabled.

Try to acquire the reset semaphore for reading before accessing the
hardware, and hold it across the counter and scanout-position reads.
If reset is already in progress, return DRM's cached software vblank
count instead. This avoids blocking behind reset and avoids accessing
display hardware while it is being reset.

The cached count is less accurate than the hardware count, but is
used only when reset prevents a safe hardware read. This addresses
the reset-time warning from this vblank path; it does not suppress or
fix unrelated lockdep warnings.

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Sunpeng Li <sunpeng.li@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Sunpeng Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

0 files changed, 0 insertions, 0 deletions