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

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Date:   Fri, 3 Feb 2023 22:15:50 +0000
From:   Frank Li <frank.li@....com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Shunsuke Mie <mie@...l.co.jp>
CC:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Wang <jasowang@...hat.com>, Jon Mason <jdmason@...zu.us>,
        Ren Zhijie <renzhijie2@...wei.com>,
        Takanari Hayama <taki@...l.co.jp>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: RE: [EXT] Re: [RFC PATCH 4/4] PCI: endpoint: function: Add EP
 function driver to provide virtio net device

> 
> 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@...l.co.jp>
> > Signed-off-by: Takanari Hayama <taki@...l.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. 

> >  .../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.

> >  drivers/pci/endpoint/functions/pci-epf-vnet.c | 387 +++++++++++

This file setup dma transfer according virtio-ring.
How about pci-epf-virtio-dma.c ?

> > +
> > +     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@nxp.com/T/#u

but it may need update host side pci virtio driver. 

> > +     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