Re: [PATCH v1 07/10] hw/arm: xenpvh: Reverse virtio-mmio creation order

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 12 Aug 2024, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>
> 
> We've been creating the virtio-mmio devices in forwards order
> but since the qbus lists prepend (rather than append) entries,
> the virtio busses end up with decreasing base address order.
> 
> Xen enables virtio-mmio nodes in forwards order so there's been
> a missmatch. So far, we've been working around this with an
> out-of-tree patch to Xen.
> 
> This reverses the order making sure the virtio busses end up
> ordered with increasing base addresses avoiding the need to
> patch Xen.
> 
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  hw/xen/xen-pvh-common.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/xen/xen-pvh-common.c b/hw/xen/xen-pvh-common.c
> index 0d368398d0..69a2dbdb6d 100644
> --- a/hw/xen/xen-pvh-common.c
> +++ b/hw/xen/xen-pvh-common.c
> @@ -73,7 +73,18 @@ static void 
> xen_create_virtio_mmio_devices(XenPVHCommonState *s)
>  {
>      int i;
>  
> -    for (i = 0; i < s->cfg.virtio_mmio_num; i++) {
> +    /*
> +     * We create the transports in reverse order. Since qbus_realize()
> +     * prepends (not appends) new child buses, the decrementing loop below 
> will
> +     * create a list of virtio-mmio buses with increasing base addresses.
> +     *
> +     * When a -device option is processed from the command line,
> +     * qbus_find_recursive() picks the next free virtio-mmio bus in forwards
> +     * order.
> +     *
> +     * This is what the Xen tools expect.
> +     */
> +    for (i = s->cfg.virtio_mmio_num - 1; i >= 0; i--) {
>          hwaddr base = s->cfg.virtio_mmio.base + i * s->cfg.virtio_mmio.size;
>          qemu_irq irq = qemu_allocate_irq(xen_set_irq, NULL,
>                                           s->cfg.virtio_mmio_irq_base + i);
> -- 
> 2.43.0
>