Re: [PATCH v7 15/18] NTB: Add support for EPF PCI-Express Non-Transparent Bridge

Arnd Bergmann
2020-11-16T15:37:25Z

On Mon, Nov 16, 2020 at 6:19 AM Kishon Vijay Abraham I <kishon@ti.com> wrote:
> On 12/11/20 6:54 pm, Arnd Bergmann wrote:
> >
> > This looks very promising indeed, I need to read up on the whole
> > discussion there. I also see your slides at [1] that help do explain some
> > of it. I have one fundamental question that I can't figure out from
> > the description, maybe you can help me here:
> >
> > How is the configuration managed, taking the EP case as an
> > example? Your UseCase1 example sounds like the system that owns
> > the EP hardware is the one that turns the EP into a vhost device,
> > and creates a vhost-rpmsg device on top, while the RC side would
> > probe the pci-vhost and then detect a virtio-rpmsg device to talk to.
>
> That's correct. Slide no 9 in [1] should give the layering details.
>
> > Can it also do the opposite, so you end up with e.g. a virtio-net
> > device on the EP side and vhost-net on the RC?
>
> Unfortunately no. Again referring slide 9 in [1], we only have
> vhost-pci-epf on the EP side which only creates a "vhost_dev" to deal
> with vhost side of things. For doing the opposite, we'd need to create
> virtio-pci-epf for EP side that interacts with core virtio (and also the
> corresponding vhost back end on PCI host).

Ok, I see. So I think this is the opposite of drivers/misc/mic and
the bluefield driver were using, so we would probably end up
needing both.

Then again, I guess the NTB driver would give us the functionality
for free, if it shows a symmetric link?

Arnd