Re: [PATCH 07/11] hw/arm/virt: add plug handler for TPM on SysBus

[Joelle van Dyne]

On Thu, Jul 13, 2023 at 8:31 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Thu, 13 Jul 2023 at 04:52, Joelle van Dyne <j@getutm.app> wrote:
> >
> > TPM needs to know its own base address in order to generate its DSDT
> > device entry.
> >
> > Signed-off-by: Joelle van Dyne <j@getutm.app>
> > ---
> >  hw/arm/virt.c | 37 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 7d9dbc2663..432148ef47 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -2732,6 +2732,37 @@ static void virt_memory_plug(HotplugHandler 
> > *hotplug_dev,
> >                           dev, &error_abort);
> >  }
> >
> > +#ifdef CONFIG_TPM
> > +static void virt_tpm_plug(VirtMachineState *vms, TPMIf *tpmif)
> > +{
> > +    PlatformBusDevice *pbus = PLATFORM_BUS_DEVICE(vms->platform_bus_dev);
> > +    hwaddr pbus_base = vms->memmap[VIRT_PLATFORM_BUS].base;
> > +    SysBusDevice *sbdev = SYS_BUS_DEVICE(tpmif);
> > +    MemoryRegion *sbdev_mr;
> > +    hwaddr tpm_base;
> > +    uint64_t tpm_size;
> > +
> > +    if (!sbdev || !object_dynamic_cast(OBJECT(sbdev), 
> > TYPE_SYS_BUS_DEVICE)) {
> > +        return;
> > +    }
> > +
> > +    tpm_base = platform_bus_get_mmio_addr(pbus, sbdev, 0);
> > +    assert(tpm_base != -1);
> > +
> > +    tpm_base += pbus_base;
> > +
> > +    sbdev_mr = sysbus_mmio_get_region(sbdev, 0);
> > +    tpm_size = memory_region_size(sbdev_mr);
> > +
> > +    if (object_property_find(OBJECT(sbdev), "baseaddr")) {
> > +        object_property_set_uint(OBJECT(sbdev), "baseaddr", tpm_base, 
> > NULL);
> > +    }
> > +    if (object_property_find(OBJECT(sbdev), "size")) {
> > +        object_property_set_uint(OBJECT(sbdev), "size", tpm_size, NULL);
> > +    }
> > +}
> > +#endif
>
> I do not like the "platform bus" at all -- it is a nasty hack.
> If the virt board needs a memory mapped TPM device it should probably
> just create one, the same way we create our other memory mapped
> devices. But...
>
> How are TPM devices typically set up/visible to the guest on
> real Arm server hardware ? Should this be a sysbus device at all?

+Alexander Graf who may answer this better.

My understanding is that we need to do this for the device to know its
own address which it needs to return in a register. On ISA devices, it
is always mapped to the same physical address so there's no issues but
for Virt machines, device addresses are dynamically allocated by the
PlatformBusDevice so only at this late stage can we tell the device
what its own address is.

>
> thanks
> -- PMM

Also to Stefan's question on consolidating code: that is ideal but
currently, it seems like much platform setup code is duplicated
amongst the various architecture's Virt machines. There would have to
be a larger effort in de-duplicating a lot of that code. Indeed, we
try to do this already with some of the ACPI stuff in the other
patches. For this specifically, we would need to know the platform
bus' base address which is done differently in ARM64's Virt and in
Loongarch's Virt. All we did was delete some existing duplicated code
and replace it with a different duplicated code :)