Peter,
On 01/30/15 05:31, Laszlo Ersek wrote:
> Signed-off-by: Laszlo Ersek <ler...@redhat.com>
> ---
> hw/arm/virt.c | 32 ++++++++++++++++++++++++++++----
> 1 file changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 2353440..091e5ee 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -441,10 +441,27 @@ static void create_virtio_devices(const VirtBoardInfo
> *vbi, qemu_irq *pic)
> int i;
> hwaddr size = vbi->memmap[VIRT_MMIO].size;
>
> - /* Note that we have to create the transports in forwards order
> - * so that command line devices are inserted lowest address first,
> - * and then add dtb nodes in reverse order so that they appear in
> - * the finished device tree lowest address first.
> + /* We create the transports in forwards order. Since qbus_realize()
> + * prepends (not appends) new child buses, the incrementing loop below
> will
> + * create a list of virtio-mmio buses with decreasing 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. The upshot is that -device options in increasing command line
> + * order are mapped to virtio-mmio buses with decreasing base addresses.
> + *
> + * When this code was originally written, that arrangement ensured that
> the
> + * guest Linux kernel would give the lowest "name" (/dev/vda, eth0, etc)
> to
> + * the first -device on the command line. (The end-to-end order is a
> + * function of this loop, qbus_realize(), qbus_find_recursive(), and the
> + * guest kernel's name-to-address assignment strategy.)
> + *
> + * Meanwhile, the kernel's traversal seems to have been reserved; see eg.
can you please s/reserved/reversed/?
Result of over-editing, sorry.
Thanks
> + * the message, if not necessarily the code, of commit 70161ff336.
> + * Therefore the loop now establishes the inverse of the original intent.
> + *
> + * Unfortunately, we can't counteract the kernel change by reversing the
> + * loop; it would break existing command lines.
> */
> for (i = 0; i < NUM_VIRTIO_TRANSPORTS; i++) {
> int irq = vbi->irqmap[VIRT_MMIO] + i;
> @@ -453,6 +470,13 @@ static void create_virtio_devices(const VirtBoardInfo
> *vbi, qemu_irq *pic)
> sysbus_create_simple("virtio-mmio", base, pic[irq]);
> }
>
> + /* We add dtb nodes in reverse order so that they appear in the finished
> + * device tree lowest address first.
> + *
> + * Note that this mapping is independent of the loop above. The previous
> + * loop influences virtio device to virtio transport assignment, whereas
> + * this loop controls how virtio transports are laid out in the dtb.
> + */
> for (i = NUM_VIRTIO_TRANSPORTS - 1; i >= 0; i--) {
> char *nodename;
> int irq = vbi->irqmap[VIRT_MMIO] + i;
>
