drm/amdgpu: add AMDGPU_BO_INVALID_OFFSET

An invalid offset to be used by custom VRAM/GGT manager when we
don't have an offset for an BO.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_object.c

@@ -956,6 +956,7 @@ u64 amdgpu_bo_gpu_offset(struct amdgpu_bo *bo)
 		     !amdgpu_ttm_is_bound(bo->tbo.ttm));
 	WARN_ON_ONCE(!ww_mutex_is_locked(&bo->tbo.resv->lock) &&
 		     !bo->pin_count);
+	WARN_ON_ONCE(bo->tbo.mem.start == AMDGPU_BO_INVALID_OFFSET);
 
 	return bo->tbo.offset;
 }

drivers/gpu/drm/amd/amdgpu/amdgpu_object.h

@@ -31,6 +31,8 @@
 #include <drm/amdgpu_drm.h>
 #include "amdgpu.h"
 
+#define AMDGPU_BO_INVALID_OFFSET	LONG_MAX
+
 /**
  * amdgpu_mem_type_to_domain - return domain corresponding to mem_type
  * @mem_type:	ttm memory type