Re: [PATCH 1/6] net: hisilicon: add support for hisi_femac core on Hi3798MV200

[Yang Xiwen]

On 2/16/2024 9:23 PM, Andrew Lunn wrote:
> > +	// Register the optional MDIO bus
> > +	for_each_available_child_of_node(node, mdio_np) {
> > +		if (of_node_name_prefix(mdio_np, "mdio")) {
> > +			priv->mdio_pdev = of_platform_device_create(mdio_np, NULL, dev);
> > +			of_node_put(mdio_np);
> > +			if (!priv->mdio_pdev) {
> > +				dev_err(dev, "failed to register MDIO bus device\n");
> > +				goto out_free_netdev;
> > +			}
> > +			mdio_registered = true;
> > +			break;
> > +		}
> > +	}
> > +
> > +	if (!mdio_registered)
> > +		dev_warn(dev, "MDIO subnode notfound. This is usually a bug.\n");
> I don't understand the architecture of this device yet...
>
> It seems like you have an integrated PHY? In the example, you used a
> phy-handle to bind the MAC to the PHY. So why is the MDIO bus
> optional?
Because the MAC can also support external PHY according to the 
datasheet. Maybe some other SoCs didn't implement this internal PHY and 
used an external PHY instead.
> Do the MII signals from the MAC also go to SoC pins, so you could use
> an external PHY? Is there a SERDES so you could connect to an SFP
> cage?
No. MII signals is not accessible outside of the SoC. The SoC only 
exports FEPHY pins (i.e. RXN(P) and TXN(P)).
> Also, do the MDIO pins go to SoC pins? Can the MDIO bus master be used
> to control external PHYs?
It can, but not for Hi3798MV200. The datasheet said it can use both 
internal phy or external phy. But for Hi3798MV200, seems impossible.
> If everything is internal, fixed in silicon, no variation possible,
> you don't need to describe the MDIO bus in DT. The MAC driver can
> register it, and then get the PHY at the hard coded address it uses.
>
> 	 Andrew


--
Regards,
Yang Xiwen