PCI ENDPOINT FRAMEWORK Kishon Vijay Abraham I 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.