netdev - Re: [PATCH 4/4] asix: Add a new driver for the AX88172A

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Date:	Sun, 08 Jul 2012 17:39:35 +0200
From:	Michael Riesch <michael@...sch.at>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Christian Riesch <christian.riesch@...cron.at>,
	netdev@...r.kernel.org, Oliver Neukum <oneukum@...e.de>,
	Eric Dumazet <edumazet@...gle.com>,
	Allan Chou <allan@...x.com.tw>,
	Mark Lord <kernel@...savvy.com>,
	Grant Grundler <grundler@...omium.org>,
	Ming Lei <tom.leiming@...il.com>
Subject: Re: [PATCH 4/4] asix: Add a new driver for the AX88172A

On Fri, 2012-07-06 at 18:37 +0100, Ben Hutchings wrote:
> > +	priv->mdio->priv = (void *)dev;
> > +	priv->mdio->read = &asix_mdio_bus_read;
> > +	priv->mdio->write = &asix_mdio_bus_write;
> > +	priv->mdio->name = "Asix MDIO Bus";
> > +	snprintf(priv->mdio->id, MII_BUS_ID_SIZE, "asix-%s",
> > +		 dev_name(dev->net->dev.parent));
> [...]
> 
> I think you need to ensure that the bus identifier is unique throughout
> its lifetime, but net devices can be renamed and that could lead to a
> collision.  Perhaps you could use the ifindex or the USB device path

Ben,

the dev_name function in the code above returns the sysfs filename of
the USB device (e.g. 1-0:1.0).

> (though that might be too long).

This may be a problem. The bus identifier may be 17 characters long, so
if we leave the endpoint/configuration part (:1.0) and the prefix away
it should be fine in any "normal" system. However, on a system with a
more-than-9-root-hubs 5-tier 127-devices-each USB infrastructure it
results in collisions. So is this approach acceptable?

Using the ifindex sounds good to me,

snprintf(priv->mdio->id, MII_BUS_ID_SIZE, "asix-%d",
	dev->net->ifindex);

works on any system with less than 10^12 network interfaces.

Regards,
Michael



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