REG_FRAME_FORMAT_W_DLC
ffw |= FIELD_PREP(REG_FRAME_FORMAT_W_DLC, can_fd_len2dlc(cf->len));
if (FIELD_GET(REG_FRAME_FORMAT_W_DLC, ffw) <= 8) {
len = FIELD_GET(REG_FRAME_FORMAT_W_DLC, ffw);