# Re: \[PATCH\] vdpa/mlx5: set\_features should allow reset to zero

- From: Michael S. Tsirkin \<mst@redhat.com\>
- Date: 2021-02-24 08:48:19 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/02/6277493
- Thread: https://ratatoskr.run/netdev/2021/02/6277493/t.md

```text
On Wed, Feb 24, 2021 at 04:26:43PM +0800, Jason Wang wrote:
>     Basically on first guest access QEMU would tell kernel whether
>     guest is using the legacy or the modern interface.
>     E.g. virtio_pci_config_read/virtio_pci_config_write will call ioctl(ENABLE_LEGACY, 1)
>     while virtio_pci_common_read will call ioctl(ENABLE_LEGACY, 0)
> 
> 
> But this trick work only for PCI I think?
> 
> Thanks

ccw has a revision it can check. mmio does not have transitional devices
at all.

-- 
MST

```