netdev - mii_bus->read return checking in phy

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Date:	Fri, 4 Mar 2011 18:25:48 +0100
From:	Florian Fainelli <florian@...nwrt.org>
To:	netdev@...r.kernel.org
Cc:	David Miller <davem@...emloft.net>,
	Andy Fleming <afleming@...escale.com>
Subject: mii_bus->read return checking in phy_device.c

Hello Andy,

While debugging a PHY probing issue with the au1000_eth, I stumbled upon this 
in drivers/net/phy/phy_device.c:

        phy_reg = bus->read(bus, addr, MII_PHYSID1);                                                  

        if (phy_reg < 0)                        
                return -EIO;

most drivers implement phylib's mdio_read callback by simply returning the 
contents of their MDIO register after a readl, ioread ... which is unsigned. 
Would not it rather make sense to check for phy_reg <= 0 instead?

This can lead for instance to believing that a PHY is present at a wrong 
address because the MDIO read function returns 0 for that particular register, 
which is logical because no PHY is present at that address.

I am asking in case I just miss something.

Thank you.
--
Florian
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