PCI ENDPOINT FRAMEWORK
		    Kishon Vijay Abraham I <kishon@ti.com>

This document is a guide to use the PCI Endpoint Framework in order to create
endpoint controller driver, endpoint function driver and using configfs
interface to bind the function driver to the controller driver.

1. Introduction

*Linux* has a comprehensive PCI subsystem to support PCI controllers that
operates in Root Complex mode. The subsystem has capability to scan PCI bus,
assign memory resources and irq resources, load PCI driver (based on
vendorid, deviceid), support other services like hot-plug, power management,
advanced error reporting and virtual channels.

However PCI controller IPs integrated in certain SoC is capable of operating
either in Root Complex mode or Endpoint mode. PCI Endpoint Framework will
add endpoint mode support in *Linux*. This will help to run Linux in an
EP system which can have a wide variety of use cases from testing or
validation, co-processor accelerator etc..

2. PCI Endpoint Core

The PCI Endpoint Core layer comprises of 3 components: the Endpoint Controller
library, the Endpoint Function library and the configfs layer to bind the
endpoint function with the endpoint controller.

2.1 PCI Endpoint Controller(EPC) Library

The EPC library provides APIs to be used by the controller that can operate
in endpoint mode. It also provides APIs to be used by function driver/library
in order to implement a particular endpoint function.

2.1.1 APIs for the PCI controller Driver

This section lists the APIs that the PCI Endpoint core provides to be used
by the PCI controller driver.

*) devm_pci_epc_create()/pci_epc_create()

   The PCI controller driver should implement the following ops:
	 * write_header: ops to populate configuration space header
	 * set_bar: ops to configure the BAR
	 * clear_bar: ops to reset the BAR
	 * alloc_addr_space: ops to allocate *in* PCI controller address space
	 * free_addr_space: ops to free the allocated address space
	 * raise_irq: ops to raise a legacy or MSI interrupt
	 * start: ops to start the PCI link
	 * stop: ops to stop the PCI link

   The PCI controller driver can then create a new EPC device by invoking
   devm_pci_epc_create/pci_epc_create.

*) devm_pci_epc_destroy()/pci_epc_destroy()

   The PCI controller driver can destroy the EPC device created by either
   devm_pci_epc_create or pci_epc_create using devm_pci_epc_destroy() or
   /pci_epc_destroy()

2.1.2 APIs for the PCI Endpoint Function Driver

This section lists the APIs that the PCI Endpoint core provides to be used
by the PCI endpoint function driver.

*) pci_epc_write_header()

   The PCI endpoint function driver should use pci_epc_write_header() to
   write the standard configuration header to the endpoint controller.

*) pci_epc_set_bar()

   The PCI endpoint function driver should use pci_epc_set_bar() to configure
   the Base Address Register in order for the host to assign PCI addr space.
   Register space of the function driver is usually configured
   using this API.

*) pci_epc_clear_bar()

   The PCI endpoint function driver should use pci_epc_clear_bar() to reset
   the BAR.

*) pci_epc_raise_irq()

   The PCI endpoint function driver should use pci_epc_raise_irq() to raise
   Legacy Interrupt or MSI Interrupt.

*) pci_epc_start()

   The PCI endpoint function driver should invoke pci_epc_start() once it
   has configured the endpoint function and wants to start the PCI link.

*) pci_epc_stop()

   The PCI endpoint function driver should invoke pci_epc_stop() to stop
   the PCI LINK.

2.1.3 APIs for the PCI Endpoint Function Library

This section lists the APIs that the PCI Endpoint core provides to be used
by the PCI endpoint function library.

*) pci_epc_bind_epf()

   The PCI endpoint function library uses pci_epc_bind_epf() to bind the
   function driver with a controller driver. The binding will be based on
   the endpoint controller function name (as seen in /sys/class/pci_epc/).

*) pci_epc_unbind_epf()

   The PCI endpoint function library uses pci_epc_unbind_epf() to unbind
   the function driver from the controller driver. After unbind the controller
   driver can be bound to any other function driver.

2.2 PCI Endpoint Function(EPF) Library

The EPF library provides APIs to be used by the function driver and the EPC
library in order to provide endpoint mode functionality.

2.2.1 APIs for the PCI Endpoint Function Driver

This section lists the APIs that the PCI Endpoint core provides to be used
by the PCI endpoint function driver.

*) pci_epf_register_driver()

   The PCI Endpoint Function driver should implement the following ops:
	 * bind: ops to perform when a EPC device has been bound to EPF device
	 * unbind: ops to perform when a binding has been lost between a EPC
	   device and EPF device
	 * linkup: ops to perform when the EPC device has established a
	   connection with a host system

  The PCI Function driver can then register the PCI EPF driver by using
  pci_epf_register_driver().

*) pci_epf_unregister_driver()

  The PCI Function driver can unregister the PCI EPF driver by using
  pci_epf_unregister_driver().

*) pci_epf_alloc_space()

  The PCI Function driver can allocate space for a particular BAR using
  pci_epf_alloc_space().

*) pci_epf_free_space()

  The PCI Function driver can free the allocated space
  (using pci_epf_alloc_space) by invoking pci_epf_free_space().

2.2.2 APIs for the PCI Endpoint Controller Library

This section lists the APIs that the PCI Endpoint core provides to be used
by the PCI endpoint controller library.

*) pci_epf_bind()

   The PCI endpoint controller library invokes pci_epf_bind() when the EPF
   device has been bound to a EPC device.

*) pci_epf_unbind()

   The PCI endpoint controller library invokes pci_epf_unbind() when the
   binding between EPC device and EPF device is lost.

*) pci_epf_linkup()

   The PCI endpoint controller library invokes pci_epf_linkup() when the
   EPC device has established the connection to the host.

2.3 CONFIGFS

The PCI Endpoint Core exposes configfs entry (pci_ep) in order to configure the
PCI Endpoint Function and in order to bind the endpoint function
with the endpoint controller. Every folder in pci_ep/ represent a PCI
endpoint function.

The following entries can be used to configure the standard configuration
header of the endpoint function.
	vendorid
	deviceid
	revid
	progif_code
	subclass_code
	baseclass_code
	cache_line_size
	subsys_vendor_id
	subsys_id
	interrupt_pin

The following entries has special meaning:
	function: this readonly entry shows the name using which the function
		  driver will be bound to this function
	epc	: the name of the EPC device this function should be bound to.
		  The name of the EPC device should be from /sys/class/pci_epc.

3. Known Limitations

The Endpoint Core doesn't support adding multi-function devices.