netdev - Re: [PATCH 1/6] net: hisilicon: add support for hisi

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Message-ID: <d3ac4638-d0bf-4c6c-bccd-519ad1f4dc5e@lunn.ch>
Date: Fri, 16 Feb 2024 14:23:17 +0100
From: Andrew Lunn <andrew@...n.ch>
To: forbidden405@...look.com
Cc: Yisen Zhuang <yisen.zhuang@...wei.com>,
	Salil Mehta <salil.mehta@...wei.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Yang Xiwen <forbidden405@...mail.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/6] net: hisilicon: add support for hisi_femac core on
 Hi3798MV200

> +	// 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?

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?

Also, do the MDIO pins go to SoC pins? Can the MDIO bus master be used
to control external PHYs?

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