dma_map_sg
nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
nents = dma_map_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);