Re: [RFC PATCH v2 3/3] PCI: endpoint: Add EP function driver to provide virtio-console functionality

From: Shunsuke Mie
Date: Tue May 09 2023 - 23:18:04 EST

Hi Json,
2023年5月8日(月) 13:03 Jason Wang <jasowang@xxxxxxxxxx>:
>
> On Thu, Apr 27, 2023 at 6:44 PM Shunsuke Mie <mie@xxxxxxxxxx> wrote:
> >
> > Add a new PCIe endpoint function driver that works as a pci virtio-console
> > device. The console connect to endpoint side console. It enables to
> > communicate PCIe host and endpoint.
> >
> > Architecture is following:
> >
> > ┌────────────┐ ┌──────────────────────┬────────────┐
> > │virtioe │ │ │virtio │
> > │console drv │ ├───────────────┐ │console drv │
> > ├────────────┤ │(virtio console│ ├────────────┤
> > │ virtio bus │ │ device) │◄────►│ virtio bus │
> > ├────────────┤ ├---------------┤ └────────────┤
> > │ │ │ pci ep virtio │ │
> > │ pci bus │ │ console drv │ │
> > │ │ pcie ├───────────────┤ │
> > │ │ ◄─────► │ pci ep Bus │ │
> > └────────────┘ └───────────────┴───────────────────┘
> > PCIe Root PCIe Endpoint
> >
>
> I think it might only works for peer devices like:
>
> net, console or vsock.
Could you tell me what "peer devices" means?

> So there're many choices here, I'd like to know what's the reason for
> you to implement a mediation.
>
> An alternative is to implement a dedicated net, console and vsock
> driver for vringh (CAIF somehow works like this). This would have
> better performance.
Does it mean that the driver also functions as a network driver directly?
>
>
> > This driver has two roles. The first is as a PCIe endpoint virtio console
> > function, which is implemented using the PCIe endpoint framework and PCIe
> > EP virtio helpers. The second is as a virtual virtio console device
> > connected to the virtio bus on PCIe endpoint Linux.
> >
> > Communication between the two is achieved by copying the virtqueue data
> > between PCIe root and endpoint, respectively.
> >
> > This is a simple implementation and does not include features of
> > virtio-console such as MULTIPORT, EMERG_WRITE, etc. As a result, each
> > virtio console driver only displays /dev/hvc0.
> >
> > As an example of usage, by setting getty to /dev/hvc0, it is possible to
> > login to another host.
> >
> > Signed-off-by: Shunsuke Mie <mie@xxxxxxxxxx>
> > ---
> > Changes from v2:
> > - Change to use copy functions between kiovs of pci-epf-virtio.
> >
> > drivers/pci/endpoint/functions/Kconfig | 12 +
> > drivers/pci/endpoint/functions/Makefile | 1 +
> > drivers/pci/endpoint/functions/pci-epf-vcon.c | 596 ++++++++++++++++++
> > 3 files changed, 609 insertions(+)
> > create mode 100644 drivers/pci/endpoint/functions/pci-epf-vcon.c
> >
> > diff --git a/drivers/pci/endpoint/functions/Kconfig b/drivers/pci/endpoint/functions/Kconfig
> > index fa1a6a569a8f..9ce2698b67e1 100644
> > --- a/drivers/pci/endpoint/functions/Kconfig
> > +++ b/drivers/pci/endpoint/functions/Kconfig
> > @@ -44,3 +44,15 @@ config PCI_EPF_VIRTIO
> > select VHOST_RING_IOMEM
> > help
> > Helpers to implement PCI virtio Endpoint function
> > +
> > +config PCI_EPF_VCON
> > + tristate "PCI Endpoint virito-console driver"
> > + depends on PCI_ENDPOINT
> > + select VHOST_RING
> > + select PCI_EPF_VIRTIO
> > + help
> > + PCIe Endpoint virtio-console function implementatino. This module
> > + enables to show the virtio-console as pci device to PCIe host side, and
> > + another virtual virtio-console device registers to endpoint system.
> > + Those devices are connected virtually and can communicate each other.
> > +
> > diff --git a/drivers/pci/endpoint/functions/Makefile b/drivers/pci/endpoint/functions/Makefile
> > index a96f127ce900..b4056689ce33 100644
> > --- a/drivers/pci/endpoint/functions/Makefile
> > +++ b/drivers/pci/endpoint/functions/Makefile
> > @@ -7,3 +7,4 @@ obj-$(CONFIG_PCI_EPF_TEST) += pci-epf-test.o
> > obj-$(CONFIG_PCI_EPF_NTB) += pci-epf-ntb.o
> > obj-$(CONFIG_PCI_EPF_VNTB) += pci-epf-vntb.o
> > obj-$(CONFIG_PCI_EPF_VIRTIO) += pci-epf-virtio.o
> > +obj-$(CONFIG_PCI_EPF_VCON) += pci-epf-vcon.o
> > diff --git a/drivers/pci/endpoint/functions/pci-epf-vcon.c b/drivers/pci/endpoint/functions/pci-epf-vcon.c
> > new file mode 100644
> > index 000000000000..31f4247cd10f
> > --- /dev/null
> > +++ b/drivers/pci/endpoint/functions/pci-epf-vcon.c
> > @@ -0,0 +1,596 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * PCI Endpoint function driver to impliment virtio-console device
> > + * functionality.
> > + */
> > +#include <linux/pci-epf.h>
> > +#include <linux/virtio_ids.h>
> > +#include <linux/virtio_pci.h>
> > +#include <linux/virtio_console.h>
> > +#include <linux/virtio_ring.h>
> > +
> > +#include "pci-epf-virtio.h"
> > +
> > +static int virtio_queue_size = 0x100;
> > +module_param(virtio_queue_size, int, 0444);
> > +MODULE_PARM_DESC(virtio_queue_size, "A length of virtqueue");
> > +
> > +struct epf_vcon {
> > + /* To access virtqueues on remote host */
> > + struct epf_virtio evio;
> > + struct vringh_kiov *rdev_iovs;
> > +
> > + /* To register a local virtio bus */
> > + struct virtio_device vdev;
> > +
> > + /* To access virtqueus of local host driver */
> > + struct vringh *vdev_vrhs;
> > + struct vringh_kiov *vdev_iovs;
> > + struct virtqueue **vdev_vqs;
> > +
> > + /* For transportation and notification */
> > + struct workqueue_struct *task_wq;
> > + struct work_struct raise_irq_work, rx_work, tx_work;
> > +
> > + /* To retain virtio features. It is commonly used local and remote. */
> > + u64 features;
> > +
> > + /* To show a status whether this driver is ready and the remote is connected */
> > + bool connected;
> > +};
> > +
> > +enum {
> > + VCON_VIRTQUEUE_RX,
> > + VCON_VIRTQUEUE_TX,
> > + // Should be end of enum
> > + VCON_VIRTQUEUE_NUM
> > +};
>
> It would be better if we can split the console specific thing out,
> then it allows us to do ethernet and vsock in the future.
I'm planning to implement each virtio device in a separate file.
https://lwn.net/Articles/922124/



> Thanks
>
Best regards,
Shunsuke