SWITCHTEC_INVALID_HFID
if (src_fid != SWITCHTEC_INVALID_HFID &&
dst_fid != SWITCHTEC_INVALID_HFID)
return switchtec_dma_prep_desc(c, SWITCHTEC_INVALID_HFID, dma_dst,
SWITCHTEC_INVALID_HFID, dma_src, 0, len,