netdev - Re: [PATCH] Make possible speeds known to ethtool

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Date:	Thu, 08 Jan 2009 19:25:01 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Jeff Garzik <jgarzik@...ox.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] Make possible speeds known to ethtool

On Thu, 2009-01-08 at 11:11 -0800, Rick Jones wrote:
> Jeff Garzik wrote:
> > Ben Hutchings wrote:
> >> The vetting of speeds is kind of silly.  Given that speed is established
> >> as being a number of Mbit/s (hence the need for speed_hi), why not
> >> remove the warning and the checks for known values and report it as
> >> such?
> > 
> > 
> > I'm ok with that route.  Historically it made sense, but AFAICS the 
> > driver _must_ verify the speed anyway, so removing the limitation in the 
> > userspace tool seems reasonable.
> > 
> > The next release of ethtool is coming in about 4 weeks, and we can 
> > definitely get something like this in there.
> 
> I have a simple patch which does just that ready to post, but will 
> point-out that removing the checks entirely will result in the speed 
> being reported as 65535 (without Unknown) for an interface with its 
> cable disconnected.  This however is is based only on "testing" on a 
> 2.6.24-22-generic (hardy) kernel with 7.3.20-k2-NAPI of the e1000 driver 
> driving an Intel 82566MM (rev 03).

I think 0, (u32)(-1) and (u16)(-1) may have to be special-cased as
unknown, but everything else can be treated as a number of Mbit/s.  I
don't know what a driver should do about an interface that really runs
at 65.535 Gbit/s though...

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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