[EXT] Re: [RFC PATCH 4/4] PCI: endpoint: function: Add EP function driver to provide virtio net device

Shunsuke Mie
Tue, 07 Feb 2023 10:56:02 -0000

2023?2?4?(?) 7:15 Frank Li <frank.li at nxp.com>:
>
> >
> > Caution: EXT Email
> >
> > On Fri, Feb 03, 2023 at 07:04:18PM +0900, Shunsuke Mie wrote:
> > > Add a new endpoint(EP) function driver to provide virtio-net
device. This
> > > function not only shows virtio-net device for PCIe host system,
but also
> > > provides virtio-net device to EP side(local) system. Virtualy
those network
> > > devices are connected, so we can use to communicate over IP like
a simple
> > > NIC.
> > >
> > > Architecture overview is following:
> > >
> > > to Host       |                       to Endpoint
> > > network stack |                 network stack
> > >       |       |                       |
> > > +-----------+ |       +-----------+   +-----------+
> > > |virtio-net | |       |virtio-net |   |virtio-net |
> > > |driver     | |       |EP function|---|driver     |
> > > +-----------+ |       +-----------+   +-----------+
> > >       |       |             |
> > > +-----------+ | +-----------+
> > > |PCIeC      | | |PCIeC      |
> > > |Rootcomplex|-|-|Endpoint   |
> > > +-----------+ | +-----------+
> > >   Host side   |          Endpoint side
> > >
> > > This driver uses PCIe EP framework to show virtio-net (pci)
device Host
> > > side, and generate virtual virtio-net device and register to EP
side.
> > > A communication date
> >
> > data?
> >
> > > is diractly
> >
> > directly?
> >
> > > transported between virtqueue level
> > > with each other using PCIe embedded DMA controller.
> > >
> > > by a limitation of the hardware and Linux EP framework, this
function
> > > follows a virtio legacy specification.
> >
> > what exactly is the limitation and why does it force legacy?
> >
> > > This function driver has beed tested on S4 Rcar (r8a779fa-spider)
board but
> > > just use the PCIe EP framework and depends on the PCIe EDMA.
> > >
> > > Signed-off-by: Shunsuke Mie <mie at igel.co.jp>
> > > Signed-off-by: Takanari Hayama <taki at igel.co.jp>
> > > ---
> > >  drivers/pci/endpoint/functions/Kconfig        |  12 +
> > >  drivers/pci/endpoint/functions/Makefile       |   1 +
> > >  .../pci/endpoint/functions/pci-epf-vnet-ep.c  | 343 ++++++++++
>
> It is actually that not related vnet. Just virtio.
> I think pci-epf-virtio.c is better.
Yes, it have to be.
> > >  .../pci/endpoint/functions/pci-epf-vnet-rc.c  | 635
++++++++++++++++++
>
> It is epf driver. rc is quite confused.
> Maybe you can combine pci-epf-vnet-ep.c and pci-epf-vnet-rc.c to one file.
I agree. Try to combine them
> > >  drivers/pci/endpoint/functions/pci-epf-vnet.c | 387 +++++++++++
>
> This file setup dma transfer according virtio-ring.
> How about pci-epf-virtio-dma.c ?
I attempt to rearrange the location of code and
filenames.
> > > +
> > > +     epf_vnet_rc_set_config16(vnet, VIRTIO_PCI_ISR,
> > VIRTIO_PCI_ISR_QUEUE);
> > > +     /*
> > > +      * Initialize the queue notify and selector to outside of
the appropriate
> > > +      * virtqueue index. It is used to detect change with
polling. There is no
> > > +      * other ways to detect host side driver updateing those
values
> > > +      */
>
> I am try to use gic-its or other msi controller as doorbell.
> https://lore.kernel.org/imx/20221125192729.1722913-1-Frank.Li at
nxp.com/T/#u
>
> but it may need update host side pci virtio driver.
Thanks, is it possible to use  MSI-X as well? The virtio spec
indicates to use legacy irq or
MSI-X only.
> > > +     epf_vnet_rc_set_config16(vnet, VIRTIO_PCI_QUEUE_NOTIFY,
> > default_qindex);
> > > +     epf_vnet_rc_set_config16(vnet, VIRTIO_PCI_QUEUE_SEL,
> > default_qindex);
> > > +     /* This pfn is also set to 0 for the polling as well */
> > > +     epf_vnet_rc_set_config16(vnet, VIRTIO_PCI_QUEUE_PFN, 0);
> > > +
> > --
> > > 2.25.1
>
Best,
Shunsuke.