PCI: endpoint: Add EP function driver to provide virtio-console funct…

…ionality

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

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@igel.co.jp>

drivers/pci/endpoint/functions/Kconfig

@@ -44,3 +44,15 @@ config PCI_EPF_VIRTIO
 	select VHOST_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.
+

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