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

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Message-ID: <505B0C00.5010003@arm.com>
Date:	Thu, 20 Sep 2012 13:28:48 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	Pawel Moll <Pawel.Moll@....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>
Subject: Re: [PATCH] arm: introduce a DTS for Xen unprivileged virtual machines

On 20/09/12 13:15, Stefano Stabellini wrote:
> 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.

I think the important thing here is that the memory map is RS1. As this
is a (very limited) subset of a vexpress A15, it seems to make some sense.

I still think it is useful at have an example of such a platform in the
tree, if only as a very minimal example.

	M.
-- 
Jazz is not dead. It just smells funny...

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