linux-kernel - Re: [PATCH net-next 1/3] net: nixge: Add support for fixed-link subnodes

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Date:   Thu, 30 Aug 2018 19:54:19 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Moritz Fischer <moritz.fischer@...us.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org, Alex Williams <alex.williams@...com>
Subject: Re: [PATCH net-next 1/3] net: nixge: Add support for fixed-link
 subnodes

> > The hardware has MDIO, but you don't have a PHY connected on it, and
> > use fixed link.
> 
> Since it's an FPGA design in that case we'd probably build the hardware without
> MDIO to save resources.

You can save resources, but is it worth the complexity else where,
like in the software?

> > It is important you have the mdio subnode, with PHYs and switches as
> > children. The driver currently gets this wrong, it uses
> > pdev->dev.of_node.
> 
> Oh, whoops.

Yes, and i also missed it. I generally review all new network drivers
and look at their MDIO and PHY code.

> Any good examples of drivers doing it right? Is the one going with
> the DT snippet above a good example?

That comes from the Freescale fec_main.c. It only supports DT, and
always uses of_mdiobus_register. You need to be a bit more flexible
for when you don't have DT. I'm not sure there are good example of
this, since they either don't need this flexibility, or they get it
wrong :-(

      Andrew