[PATCH] arm: introduce a DTS for Xen unprivileged virtual machines

On Thu, 2012-09-20 at 12:56 +0100, Stefano Stabellini wrote:

On Thu, 20 Sep 2012, Ian Campbell wrote:

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On Wed, 2012-09-19 at 18:44 +0100, Stefano Stabellini wrote:

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+/include/ "skeleton.dtsi"
+
+/ {
+	model = "XENVM-4.2";

Why the shouty caps?

It looks like that model names are always capital, at least in the
vexpress family.

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Did you mean 4.3 here and throughout?

Nope, after all this is the fruit of the work we did on Xen 4.2, mostly
already upstream. By the time of the 4.3 release we might have a
different dts.

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+	compatible = "xen,xenvm-4.2", "arm,vexpress";

Is this second compatible thing actually true? We don't actually emulate
much (anything?) of what would be on a real vexpress motherboard.

"arm,vexpress" is used only in v2m.c and I don't think we want the
majority of that -- we don't provide any of the peripherals which it
registers.

I think the only things we might want out of that lot are the arch timer
and perhaps the uart0 (as a debug port).

I suspect we should have our own xen machine .c.

[...]

It is true that we are "arm,vexpress" compatible at the moment.

But we aren't, we don't emulate 90%+ of the actual hardware which
vexpress compatibility would actually imply.

Look in arch/arm/mach-vexpress/v2m.c, which is the only thing keyed off
this compat value -- it's full of stuff which we don't (and aren't going
to) implement.

Also we need to be unless we want to introduce our own arch/arm/mach-xen
that I think is overkill.

Probably.

Versatile Express is flexible enough to be a good base for our own
virtual machine platform, especially if the maintainers keep an eye on
getting everything through DT and not expecting devices just to be there
;-)

Perhaps what we want is a stricter subset of the stuff in mach-vexpress
then. But if so then this should be expressed both in the DT and in the
code, not just papered over by declaring things compatible when they are
not.

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+	gic: interrupt-controller at 2c001000 {
+		compatible = "arm,cortex-a9-gic";

Don't we mean "arm,cortex-a15-gic" here? That's what we actually
provide. I'm not sure how the a9 and a15 differ.

The GIC that comes with vexpress is a9 compatible.

The GIC which Xen emulates is the one which matters here though, and
that is an a15.

Ian.