Re: [RFC PATCH v2 10/11] hw/arm/smmuv3: Populate OAS based on CPU PARANGE

[Peter Maydell]

On Tue, 21 Mar 2023 at 13:55, Mostafa Saleh <smostafa@google.com> wrote:
>
> Hi Peter,
>
> On Tue, Mar 21, 2023 at 01:34:55PM +0000, Peter Maydell wrote:
> > > >>> +     */
> > > >>> +    ARMCPU *armcpu = ARM_CPU(qemu_get_cpu(0));
> > > >>> +    uint8_t oas = FIELD_EX64(armcpu->isar.id_aa64mmfr0, 
> > > >>> ID_AA64MMFR0, PARANGE);
> > > >> is this working in accelerated mode?
> > > > I didn't try with accel, I will give it a try, but from what I see, that
> > > > ARM_CPU() is used to get the CPU in traget/arm/kvm.c which is used from
> > > > accel/kvm-all.c, so it seems this would work for accelerated mode.
> > >
> > > yeah I ma not familiar enough with that code but it is worth to be 
> > > checked.
> >
> > I'm a bit unsure about fishing around in the CPU ID registers for this.
> > That's not what you would do in real hardware, you'd just say "the
> > system is supposed to configure the CPU and the SMMU correctly".
> >
> > Also, there is no guarantee that CPU 0 is related to this SMMU in
> > particular.
> Sorry, missed this point in last email.
>
> So, we leave it this way, or there is a better way to discover PARANGE?

If you really need to know it, put a QOM property on the SMMU device
and have the board code set it. (This is analogous to how it works
in hardware: there are tie-off signals on the SMMU for the OAS value.)

-- PMM