USE_REAL_VBLANKSTART  574 drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h #define USE_REAL_VBLANKSTART		(1 << 30)
USE_REAL_VBLANKSTART  691 drivers/gpu/drm/radeon/radeon_mode.h #define USE_REAL_VBLANKSTART 		(1 << 30)