Subject: Re: [PATCH] [v8] net: emac: emac gigabit ethernet controller driver

From: Andrew Lunn <[email-masked]>
Date: Wed, 17 Aug 2016 22:05:51 +0200

> Something is odd about of_mdiobus_register().
> 
> This function scans child nodes to look for PHYs:
> 
> /* Loop over the child nodes and register a phy_device for each phy */
> for_each_available_child_of_node(np, child) {
> 	addr = of_mdio_parse_addr(&mdio->dev, child);
> 
> And in my driver, this works.  However, later when I try to call
> of_phy_find_device(), it fails.  That's because of_phy_find_device()
> wants the np of the child node.  But the only way to get that is
> with a phy-phandle property which I need to manually parse.

You do need the phy-handle, because you can have multiple PHYs, and
ethernet switches on the MDIO bus. You need to indicate which of those
PHYs is connected to this MAC.

> So what's the point of having of_mdiobus_register() parse child
> nodes, if you need a phy-phandle pointer anyway?

So we know about the other phys and switches on the MDIO bus, can load
the driver for them, etc. This is standard policy for a bus
driver. When you instantiate the bus, you enumerate it to see what is
connected to it. You do that either with of_mdiobus_register() or
mdiobus_register().

However, i do agree about having a helper do the phy-handle parsing
would be nice, and it should also handle fixed phys as well.

      Andrew
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