linux-kernel - Re: [RFC v2] virtio: add virtio-over-PCI driver

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Message-Id: <200902270044.53683.arnd@arndb.de>
Date:	Fri, 27 Feb 2009 00:44:52 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Ira Snyder <iws@...o.caltech.edu>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan-Bernd Themann <THEMANN@...ibm.com>,
	linuxppc-dev@...abs.org, netdev@...r.kernel.org
Subject: Re: [RFC v2] virtio: add virtio-over-PCI driver

On Friday 27 February 2009, Ira Snyder wrote:
> On Thu, Feb 26, 2009 at 11:34:33PM +0100, Arnd Bergmann wrote:
> > I guess the best option for doing it in Linux then would be to have
> > a board control driver (not sure if this already exists) that exports
> > high-level functions to set up the inbound and outbound windows.
> > 
> 
> Nothing like it exists. The OF device tree doesn't even describe these
> registers. The code in arch/powerpc/sysdev/fsl_pci.c uses some registers
> near these, but it gets their address by masking the low bits off the
> addresses from the device tree and adding the offsets of the new
> registers. Nasty.
> 
> I'll do this for now:
> 1) Get the message unit registers from my device tree
> 2) Encapsulate all use of get_immrbase() to a single function
> 
> That way it could be easily replaced in the future when something more
> suitable comes along.

Ok. However, I don't expect this to get fixed magically. Ideally,
you would start a new file for the board control in arch/powerpc/sysdev
and export the function from there, otherwise you do it the way you
suggested.
Then we can tell the fsl_pci and other people to use the same
method and source file to access the board control.
> 
> I didn't think about this at all. This driver could be used to boot a
> (guest) system over NFS, so in that case there isn't a userspace running
> yet, to allow configuration. This is essentially my use case, though I
> haven't implemented it yet.
> 
> Also, I hate designing user interfaces :) Any concrete suggestions on
> design would be most welcome.

Don't worry about it for now, just put all the hardcoded virtio_net
specific stuff into a file separate from the hardware specific
files so that we have a nice kernel level abstraction to build a
user abstraction on top of.

	Arnd <><
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