Re: [PATCH v15 8/9] hw/arm/virt: Add the virtio-iommu device tree mappings

[Auger Eric <eric.auger@redhat.com>]

Hi Peter,

On 2/11/20 4:00 PM, Peter Maydell wrote:
> On Sat, 8 Feb 2020 at 12:01, Eric Auger <eric.auger@redhat.com> wrote:
>>
>> Adds the "virtio,pci-iommu" node in the host bridge node and
>> the RID mapping, excluding the IOMMU RID.
>>
>> This is done in the virtio-iommu-pci hotplug handler which
>> gets called only if no firmware is loaded or if -no-acpi is
>> passed on the command line. As non DT integration is
>> not yet supported by the kernel we must make sure we
>> are in DT mode. This limitation will be removed as soon
>> as the topology description feature gets supported.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> +static void create_virtio_iommu(VirtMachineState *vms, Error **errp)
>> +{
>> +    const char compat[] = "virtio,pci-iommu";
>> +    uint16_t bdf = vms->virtio_iommu_bdf;
>> +    char *node;
>> +
>> +    vms->iommu_phandle = qemu_fdt_alloc_phandle(vms->fdt);
>> +
>> +    node = g_strdup_printf("%s/virtio_iommu@%d", vms->pciehb_nodename, bdf);
>> +    qemu_fdt_add_subnode(vms->fdt, node);
>> +    qemu_fdt_setprop(vms->fdt, node, "compatible", compat, sizeof(compat));
>> +    qemu_fdt_setprop_sized_cells(vms->fdt, node, "reg",
>> +                                 1, bdf << 8, 1, 0, 1, 0,
>> +                                 1, 0, 1, 0);
>> +
>> +    qemu_fdt_setprop_cell(vms->fdt, node, "#iommu-cells", 1);
>> +    qemu_fdt_setprop_cell(vms->fdt, node, "phandle", vms->iommu_phandle);
>> +    g_free(node);
>> +
>> +    qemu_fdt_setprop_cells(vms->fdt, vms->pciehb_nodename, "iommu-map",
>> +                           0x0, vms->iommu_phandle, 0x0, bdf,
>> +                           bdf + 1, vms->iommu_phandle, bdf + 1, 0xffff - bdf);
>> +}
> 
> This function name implies that we're creating the IOMMU device
> here (which would be a weird thing to do in a hotplug callback
> for some other device), but it looks like we're only adding
> device tree nodes ?
yes the actual iommu device is created through the -device option. I can
rename into create_iommu_dt_bindings
> 
> Given that we write the FDT blob into the guest RAM on bootup,
> how does making changes to it here on hotplug (which I assume
> to be 'after boot, whenever the user hot-plugs something') work?

the virtio-iommu is not supposed to be hotplugged but rather
cold-plugged. I use this hotplug mechanism to detect its presence and
add the related dt mappings. Maybe I can add a check to detect if the
bootup is over?

Thoughts?

Eric
> 
> thanks
> -- PMM
>