Re: [Qemu-devel] [PATCH v2 2/2] hw/arm: Add Arm Enterprise machine type

[Peter Maydell]

On 25 July 2018 at 12:44, Andrew Jones <address@hidden> wrote:
> On Wed, Jul 25, 2018 at 06:46:59PM +0800, Hongbo Zhang wrote:
>> For Armv7, there is one typical platform 'vexpress', but for Armv8, no
>
> Wasn't the vexpress model designed for a specific machine?

Yes.

> Namely for
> Arm's simulator?

No.

> Is the vexpress model really something typical among
> all the Armv7 platforms?

No.

"Vexpress" is a model specifically of a development board
produced by Arm (the versatile express). It's useful if you
want to run code that runs on that devboard, but (as with
most of the devboards we model), it's not necessarily ideal,
because it has all the limitations of the real hardware it's
modelling (in this case the big ones are limited memory, no PCI).
The hardware it models is also quite old now (maybe 7 or 8 years)
and it's not really "typical" of anything. (In the primarily
embedded space where most v7 CPUs are there's not really anything
that could be described as "typical" anyway: everything is
different.)

For most people who just want to run Linux on an emulated v7 CPU,
I would recommend the "virt" board, for the same reasons I
recommend it for v8 cores.

>> such typical one, the 'virt' is typically for running workloads, one
>> example is using it under OpenStack.
>> So a 'typical' one for Armv8 is needed for firmware and OS
>> development, similar like 'vexpress' for Armv7.
>
> What is a "typical" Armv8 machine? What will a typical Armv8 machine be in
> two years?
>
> Note, I'm not actually opposed to the current definition (because I don't
> really have one myself). I'm just opposed to hard coding one.

AIUI the aim here is to provide an emulated platform that is
set up in the way that server-style armv8 machines are
recommended to be set up, so it can be used as a testbed and
demonstration for the firmware/OS software stack. The hope
is that following "best practices" results in a "typical"
machine :-)  But the word "typical" is probably not really
very helpful here...

I would expect that in the future we'd want this machine type
to evolve with the recommendations for how to build server
platform hardware, which might indeed be different in two years,
since it would be the development platform for writing/testing
the firmware/OS stack for that two-years-time hardware.

thanks
-- PMM