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

[Peter Maydell]

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?

thanks
-- PMM