Re: [dpdk-dev] [RFC 00/14] mlx5: support SubFunction

[Parav Pandit <parav@nvidia.com>]

> From: Xia, Chenbo <chenbo.xia@intel.com>
> Sent: Tuesday, June 15, 2021 4:49 PM
> 
> >
> > > Just FYI:
> > >
> > > We are introducing a new mdev bus for DPDK:
> > > http://patchwork.dpdk.org/project/dpdk/cover/20210601030644.3318-1-
> > > chenbo.xia@intel.com/
> > >
> > I am yet to read about it. But I am not sure what value does it add.
> > A user can open a vfio device using vfio subsystem and operate on it.
> > A vfio device can be a create as a result of binding PCI VF/PF to
> > vfio-pci driver or a SF by binding SF to vfio_foo driver.
> 
> Yes, in general it is the way. For vfio-mdev, it works as binding the vfio-mdev
> to parent device and echo uuid to create a virtual device. VFIO APP like
> DPDK, as you said, should work similar with VFIO UAPI for vfio-pci devices or
> mdev-based devices. But currently DPDK only cares about vfio-pci devices
> and does not care things for other cases like mdev-based pci devices. For
> example, it does not scan /sys/bus/mdev and it always uses pci bdf as device
> address, which mdev-based pci devices do not have. Therefore I sent that
> patchset.
mdev device reside on mdev bus. So dpdk should identify the mdev object by specifying bus type = mdev, and device id = uuid.
There should not be any attachment to pci as Thomas said.

> 
> > There is kernel work in progress to use vfio core as library.
> 
> OK. Could you share me some link to it? Much appreciated.
> 
[1] https://lore.kernel.org/kvm/20210603160809.15845-1-mgurtovoy@nvidia.com/

> > So we do not anticipate to use add mdev layer and uuid to create a
> > vfio device for a SF.
> 
> OK. For now, we are following the vfio-mdev standard, using UUID to create
> vfio devices.
> 
If this layer is going to work on top of VFIO devices, does it really care that is it mdev?
Can it identify the vfio device by vfio device and its UAPI in uniform way?
such as open("/dev/vfio/98" ..);


> >
> > For Intel, ADI will never has any netdevs or rdma dev?
> 
> I think technically it could have. 
Unlikely. As I explained in previous email that creating netdev, rdma dev using mdev bus was already rejected in my previous patches.
And we step forward with auxiliary bus.

> But for some devices like our dma devices,
> it's just using mdev:
> 
> https://www.spinics.net/lists/kvm/msg244417.html
Possibly yes. Some devices might live on mdev bus.
You should wait for kernel patches to be merged as Jason said.

I still think that identifying vfio device by its /dev/vfio/<id> will go long way regardless of its bus type.