netdev - Re: [PATCH net-next 4/7] tg3: Determine PCI function number in one place

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Date:	Wed, 13 Jul 2011 21:13:27 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Matt Carlson <mcarlson@...adcom.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 4/7] tg3: Determine PCI function number in one
 place

On Wed, 2011-07-13 at 12:27 -0700, Matt Carlson wrote:
> tg3 devices will need to know exactly what function number they are so
> that they can communicate their status to the other functions.  In a KVM
> environment, the function number of a device presented by the kernel
> might not be the true function number, so an alternative method to
> determine the function number is needed.
> 
> This patch used to contain an implementation for the alternative method,
> but recently we discovered a hardware bug that renders it incorrect.
> While new method is not yet known, it is still useful to consolidate the
> code that determines the PCI function to one location and use the
> results throughout the code.
[...]

Having run into (and thankfully fixed) a similar problem in sfc, I
wonder whether it would always be worthwhile to ask the hypervisor
maintainers to keep function numbers stable when passing-through
physical functions.  Any driver using PCI_FUNC() is likely to be broken
by function number changes, and 'git grep' shows there are quite a few
of them.

Ben.

-- 
Ben Hutchings, Senior Software 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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