drm/amdgpu: return IH ring drain finished if ring is empty

Sometimes IH do not setup ring wptr overflow flag after wptr exceed
rptr. As a workaround, if IH rptr equals to wptr, ring is empty,
return true to indicate IH ring checkpoint is processed, IH ring drain
is finished.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -175,7 +175,9 @@ static bool amdgpu_ih_has_checkpoint_processed(struct amdgpu_device *adev,
 		cur_rptr += ih->ptr_mask + 1;
 	*prev_rptr = cur_rptr;
 
-	return cur_rptr >= checkpoint_wptr;
+	/* check ring is empty to workaround missing wptr overflow flag */
+	return cur_rptr >= checkpoint_wptr ||
+	       (cur_rptr & ih->ptr_mask) == amdgpu_ih_get_wptr(adev, ih);
 }
 
 /**