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

[Thomas Monjalon]

11/06/2021 07:14, Xia, Chenbo:
> From: Thomas Monjalon <thomas at monjalon.net>
> > 10/06/2021 12:33, Ferruh Yigit:
> > > On 5/27/2021 2:37 PM, Xueming Li wrote:
> > > > SubFunction [1] is a portion of the PCI device, a SF netdev has its
> > own
> > > > dedicated queues(txq, rxq). A SF shares PCI level resources with other
> > > > SFs and/or with its parent PCI function. Auxiliary bus is the
> > > > fundamental of SF.
> > > >
> > > > This patch set introduces SubFunction support for mlx5 PMD driver
> > > > including class net, regex, vdpa and compress.
> > > >
> > >
> > > There is already an mdev patch, originated from long ago. Aren't
> > subfunctions
> > > presented as mdev device? If so can't we use mdev for it?
> > 
> > No unfortunately that's different.
> > mlx5 SF is based on top of auxiliary bus in the kernel/sysfs.
> 
> Just out of curiosity:
> 
> Does SF use mdev before aux bus is introduced in kernel. I see some history
> of it but am not sure: [1] seems SF was base on mdev. [2] seems BlueField
> software v2.5 is using mdev for SF. I saw it yesterday and try to figure
> out the history. Since you are here, guess you know something 😊
> 
> [1] https://patchwork.ozlabs.org/project/netdev/cover/20191107160448.20962-1-parav@mellanox.com/
> [2] https://docs.mellanox.com/display/BlueFieldSWv25011176/Mediated+Devices

Kernel maintainers rejected the use of mdev for this purpose
and suggested to use a real bus.
You can follow the discussion here:
https://lore.kernel.org/netdev/20191108205204.GB1277001@kroah.com/

Does Intel plan to use mdev for SF?

For the sake of follow-up discussion, this is the official mdev doc:
https://www.kernel.org/doc/Documentation/vfio-mediated-device.txt