unable to bind to vfio-pci

[Bruce Richardson]

On Tue, Feb 21, 2023 at 08:05:20PM +0530, Nagendra Prabhu A T wrote:
>    Hi All,
>    I am trying to bind vfio-pci using dpdk-devbind.py, But i am seeing teh
>    following error :
>    root at nat-kvm:/usr/src/dpdk-22.11/usertools# dpdk-devbind.py
>    --bind=vfio-pci 0000:51:00.0 Error: bind failed for 0000:51:00.0 -
>    Cannot bind to driver vfio-pci: [Errno 22] Invalid argument
>    root at nat-kvm:/usr/src/dpdk-22.11/usertools#
>    I see that Sarosh has faced the same issue earlier. I saw the mail
>    thread and followed all the steps mentioned there. But it dint help.
>    Can you please help.

An error like that I would attribute to one of two possible likely causes.
[There may be other causes, but these two come to mind immediately].

1. No IOMMU available for use. In this case you need to enable no-iommu
   mode for VFIO and see if that works.
2. You have other ports on the same card bound to a kernel driver. You
   cannot use one port bound to the kernel (and therefore using IOMMU
   mappings for the kernel), while another port on the same card is bound
   to userspace vfio (and therefore looking for userspace IOMMU mappings).
   If this is the case, you need to unbind the other port from the kernel,
   and leave it unbound or else also bound to vfio. It's possible that
   no-iommu mode may help here too, but I have never tested that.

Regards,
/Bruce