I've also see some dt that use {tx,rx}_internal_delay_ps inside the PHY,
and compared to doing it in the MAC, which one is the better choice?

As pointed out in another email, we prefer the PHY does the
delay. That preference is to try to make all Linux systems the same.

And since the required delay is so close to the standard 2ns, you
should just say rgmii-id, and let the PHY add the RGMII standard
required 2ns, and it should just work, no need for any other DT
properties.

       Andrew