Re: [Qemu-devel] [RFC v1 1/2] arm: Add the cortex-a9 CPU to the a9mpcore device

[Peter Maydell]

On 16 June 2014 11:58, Andreas Färber <address@hidden> wrote:
> Well, for Cortex-A9 that may work. But Cortex-A15 (and Cortex-A5x if
> existant by now) should also be refactored alongside, as proof of
> concept - can you really create num_cpu cortex-a15 CPUs on the MPCore
> for a big.LITTLE configuration? I'd be really surprised if there were
> separate MPCore devices per cluster. That would then indicate that the
> homogeneity assumption among CPUs within an MPCore is wrong and we need
> to let its parent create the CPUs rather than an MPCore property.

Not sure what the relevance of big.LITTLE is here -- QEMU
simply doesn't support heterogenous CPU configurations so
we can't model big.LITTLE at all. If we did, it would be
via having a SoC with one a15mpcore and one a7mpcore.
(This is how the hardware does it -- there are two
multicore clusters, plus some cache coherency interconnect
magic.)

> Besides, not all CPUs have an MPCore, Cortex-A8 and Cortex-A5 come to
> mind, so we should be aware that ARMCPU child<>s on the MPCore will lead
> to asymmetry between SoCs.

For the A8 and A5 the SoC object would just instantiate them
directly -- there's no equivalent in the hardware of the
"n CPUs and their private devices" layer. So I think
any asymmetry between SoCs in QEMU is just a reflection
of the differences in the hardware.

thanks
-- PMM