netdev - RE: ETHTOOL_GSET IOCTL on GigE links

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Date:	Fri, 1 Jun 2007 15:51:18 -0700
From:	"Jeff Haran" <jharan@...cade.COM>
To:	"Jeff Garzik" <jeff@...zik.org>
Cc:	<linux-net@...r.kernel.org>, "netdev" <netdev@...r.kernel.org>
Subject: RE: ETHTOOL_GSET IOCTL on GigE links

> -----Original Message-----
> From: Jeff Garzik [mailto:jeff@...zik.org] 
> Sent: Friday, June 01, 2007 3:40 PM
> To: Jeff Haran
> Cc: linux-net@...r.kernel.org; netdev
> Subject: Re: ETHTOOL_GSET IOCTL on GigE links
> 
> Jeff Haran wrote:
> > With 10/100 Mbps links it wasn't such an issue since the 
> devices tend to
> > support the same forced speeds and duplexities as they are 
> capable of
> > negotiating, but with GigE links that's not always the 
> case, at least
> > not according to what I've read. For instance, the 
> following doc from
> > Sun http://www.sun.com/blueprints/0704/817-7526.pdf says that IEEE
> > 802.3ab says you can't force 1000Base-T over copper media 
> (see page 4),
> > whereas some other physical media allow GigE to run without
> > autonegotiation (there's apparently this "serdes" interface 
> that allows
> > it, for instance).
> > 
> > Seems like there should be another field named something like
> > supported_forced to indicate what can be forced on the 
> interface. Either
> > that or some more SUPPORTED_* bits to indicate supported 
> forced modes.
> 
> 
> The 'supported' field has nothing at all to do with auto-negotiation.
> 
> The driver should list all possibilities in that field, even 
> if some are 
> ONLY supported via 'forced' selection.
> 
> 	Jeff
> 

OK, but my question remains. In the case where a device supports one set
of speeds via autonegotiation and another set via forcing, how does one
tell which speeds can be forced and which can be autonegotiated?

Thanks,

Jeff Haran
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