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

[Peter Maydell]

On Sat, 8 Feb 2020 at 12:01, Eric Auger <address@hidden> 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 <address@hidden>
>
> +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 ?

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?

thanks
-- PMM