linux-kernel - Re: [PATCH] arm: introduce a DTS for Xen unprivileged virtual machines

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Message-ID: <alpine.DEB.2.02.1209201308490.29232@kaball.uk.xensource.com>
Date:	Thu, 20 Sep 2012 13:15:07 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Pawel Moll <pawel.moll@....com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnd Bergmann <arnd@...db.de>, <marc.zyngier@....com>
Subject: Re: [PATCH] arm: introduce a DTS for Xen unprivileged virtual
 machines

On Thu, 20 Sep 2012, Pawel Moll wrote:
> On Thu, 2012-09-20 at 12:39 +0100, Stefano Stabellini wrote:
> > There are no peripherals apart from the ones that are already described
> > here (timer, gic). All the peripherals that the guest sees are virtual
> > devices that show up on xenbus (a virtual bus). In order to initialize
> > xenbus, the guest only needs the hypervisor node.  So I'll remove the
> > ranges and interrupt-map.
> 
> So all the peripherals are actually discoverable - awesome!
> 
> But the fact is that the only "vexpressness" of this tree is
> memory@...00000 and gic@...01000. The rest (not much of it ;-) is a
> "generic A15 platform". 
> 
> I understand that you had to use some "compatible" value to get
> initialization code and I'm flattered ;-) by your choice of
> "arm,vexpress", but maybe - as suggested by others - you would be better
> off with generating this stuff in runtime, by whatever tool is used to
> instantiate the guest?

Yes, it is certainly going to be generated at run time. Does it make
sense to keep an example under arch/arm/boot/dts? I think so. There must
be other platforms that actually pass the device tree to the kernel from
the firmware and still have a dts in the kernel tree, right?
If actually there are none, it is probably best to forget about this
patch :)

Regarding the choice of "arm,vexpress", there was a discussion at kernel
summit about vexpress being the right choice as a base platform for
virtual machines on ARM, even though in the Xen case it means having a
vexpress with no peripherals.
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