netdev - Re: PHC device sharing between PCI functions

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Message-ID: <1372961945.1853.9.camel@bwh-desktop.uk.level5networks.com>
Date:	Thu, 4 Jul 2013 19:19:05 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	linux-net-drivers <linux-net-drivers@...arflare.com>,
	netdev <netdev@...r.kernel.org>,
	Laurence Evans <levans@...arflare.com>
Subject: Re: PHC device sharing between PCI functions

On Thu, 2013-07-04 at 19:39 +0200, Richard Cochran wrote:
> On Thu, Jul 04, 2013 at 05:21:18PM +0100, Ben Hutchings wrote:
> > 
> > But that is the opposite of what we're talking about.  Say the card has,
> > 16 functions resulting in net devices eth0-eth15, each of which can
> > access the same physical clock.  You said it's OK to have read-only
> > aliases for a clock, so then there might be a writable /dev/ptp0 and
> > read-only /dev/ptp1-ptp15.  What is the proper association between net
> > devices and clock devices?
> 
> But the card doesn't have 16 plugs, or does it?

No, but there can be multiple ports, and multiple functions per port.
All sharing the same clock.

> I understood you to have meant that the card has one physical plug,
> shared between one host and fifteen guests. Or maybe I am total
> confused. No, I am surely confused.
> 
> Anyhow, if a host is multihomed, then ideally all of the interfaces
> share one and the same clock. But, if the only purpose of the multiple
> interfaces in the VM host is to assign them to VM guests, then I guess
> it doesn't matter very much how they appear in the VM host.

The functions that are intended to be assigned to guests will still
appear and may have a driver bound to them in the host before they are
assigned to guests.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
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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