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

[Jason Wang]

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.

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.



> 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.

Thanks