Date: Thu, 28 Apr 2016 18:32:07 +0200
From: Andrew Lunn <andrew@lunn.ch>
To: Nathan Sullivan <nathan.sullivan@ni.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Florian Fainelli <f.fainelli@gmail.com>,
        Alexandre Belloni <alexandre.belloni@free-electrons.com>
Subject: Re: [PATCH v2] net: macb: do not scan PHYs manually
Message-ID: <20160428163207.GP29024@lunn.ch>
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 <20160428155556.GA8333@nathan3500-linux-VM>
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> Hmm, are AT91 platforms special in this regard? As far as I can tell, this
> driver (macb) and Marvell PXA are the only ethernet drivers that call
> mdiobus_scan directly, and PXA does it on a known address. I do see that there
> are trees that use macb and don't have a phy listed, which is unfortunate.

How it is supposed to work is that you do one of two things:

1) Your device tree does not have an mdio node. In this case, you call
mdiobus_register() and it will perform a scan of the bus, and find the
phys.

2) Your device tree does have an MDIO node, and you list your PHYs.

Having an MDIO node and not listing the PHYs is broken...

There are however, a few broken device trees around, and a few drivers
have workarounds. e.g. davinci_mdio.c

       /* register the mii bus
         * Create PHYs from DT only in case if PHY child nodes are explicitly
         * defined to support backward compatibility with DTs which assume that
         * Davinci MDIO will always scan the bus for PHYs detection.
         */
        if (dev->of_node && of_get_child_count(dev->of_node)) {
                data->skip_scan = true;
                ret = of_mdiobus_register(data->bus, dev->of_node);
        } else {
                ret = mdiobus_register(data->bus);
        }

You probably need to do the same for AT91, count the number of
children, and it if it zero, fall back to the non-DT way. It would
also be good to print a warning to get people to fix their device
tree.

    Andrew