DP_MSTM_CAP
st = core_link_read_dpcd(link, DP_MSTM_CAP,
if (drm_dp_dpcd_read_byte(aux, DP_MSTM_CAP, &mstm_cap) < 0)
ret = drm_dp_dpcd_readb(&mtk_dp->aux, DP_MSTM_CAP, &val);