Re: Status of ARM Cortex-A55 CPU support

[Patrice Blin]

Hi,

Thanks for your answer,

> Depends on what you're trying to do. Usually for booting
> guest OSes like Linux -cpu max (or one of the other supported
> CPU models) is fine, because Linux will look at the ID registers
> to see what features are available and adjust accordingly.

Yes, I'm emulating Linux (Android), I can check if I'm missing CPU features looking as the kernel logs.

For me, mostly the missing CPU models (and possibly related features) would be Cortex-A55 and Cortex-X1.

If I compare the logs (real/emulated), I'm missing,

 - CPU features: detected: ARM errata 1165522, 1319367, or 1530923

I'm guessing qemu doesn't implement erratas

On Mon, Jun 20, 2022 at 12:41 PM Peter Maydell <peter.maydell@linaro.org> wrote:

On Mon, 13 Jun 2022 at 16:18, Patrice Blin <patrice.blin@eshard.com> wrote:
>
> Hi,
>
> As of version 7.0.50 (v7.0.0-1647-g028f2361d0), cortex-a55 is not part of the available CPUs.
> I would like to know if support is on the horizon or should I rely on -cpu max ?
>
> While googling, I found this question was asked last year
> https://www.mail-archive.com/qemu-discuss@nongnu.org/msg06242.html
>
> Since then I see neoverse-n1 was added.
>
> How close is qemu to support cortex-a55 ?

Generally we don't add new CPU model types unless there's
a specific reason to (eg we want to add a board model that
uses that specific CPU, or the CPU represents an interesting
combination of features that's helpful for people doing
firmware development with QEMU). So nobody is particularly
looking at adding Cortex-A55 support as far as I know.

You could look at the Cortex-A55 TRM and at the list of
supported emulated architectural features in
https://www.qemu.org/docs/master/system/arm/emulation.html
to see whether the A55 has anything we're missing. If there
are no missing features then adding A55 support is fairly
easy (but we're still not likely to do it unless there's
a good reason to...)

> Is -cpu max enough ?

Depends on what you're trying to do. Usually for booting
guest OSes like Linux -cpu max (or one of the other supported
CPU models) is fine, because Linux will look at the ID registers
to see what features are available and adjust accordingly.

thanks
-- PMM