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

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Date:	Mon, 9 Jul 2012 12:30:24 +0200
From:	Christian Riesch <christian.riesch@...cron.at>
To:	michael@...sch.at
Cc:	Ben Hutchings <bhutchings@...arflare.com>, 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

Hi Ben and Michael,

On Sun, Jul 8, 2012 at 5:39 PM, Michael Riesch <michael@...sch.at> wrote:
> 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.

Ok, I'll change that to use ifindex. I didn't like the mdio bus name
with lots of colons, dashes, and periods anyway...
Thank you!

Regards, Christian
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