363 lines
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ReStructuredText
363 lines
17 KiB
ReStructuredText
============
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Introduction
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============
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The RapidIO standard is a packet-based fabric interconnect standard designed for
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use in embedded systems. Development of the RapidIO standard is directed by the
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RapidIO Trade Association (RTA). The current version of the RapidIO specification
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is publicly available for download from the RTA web-site [1].
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This document describes the basics of the Linux RapidIO subsystem and provides
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information on its major components.
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1 Overview
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==========
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Because the RapidIO subsystem follows the Linux device model it is integrated
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into the kernel similarly to other buses by defining RapidIO-specific device and
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bus types and registering them within the device model.
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The Linux RapidIO subsystem is architecture independent and therefore defines
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architecture-specific interfaces that provide support for common RapidIO
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subsystem operations.
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2. Core Components
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==================
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A typical RapidIO network is a combination of endpoints and switches.
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Each of these components is represented in the subsystem by an associated data
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structure. The core logical components of the RapidIO subsystem are defined
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in include/linux/rio.h file.
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2.1 Master Port
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---------------
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A master port (or mport) is a RapidIO interface controller that is local to the
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processor executing the Linux code. A master port generates and receives RapidIO
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packets (transactions). In the RapidIO subsystem each master port is represented
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by a rio_mport data structure. This structure contains master port specific
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resources such as mailboxes and doorbells. The rio_mport also includes a unique
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host device ID that is valid when a master port is configured as an enumerating
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host.
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RapidIO master ports are serviced by subsystem specific mport device drivers
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that provide functionality defined for this subsystem. To provide a hardware
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independent interface for RapidIO subsystem operations, rio_mport structure
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includes rio_ops data structure which contains pointers to hardware specific
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implementations of RapidIO functions.
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2.2 Device
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----------
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A RapidIO device is any endpoint (other than mport) or switch in the network.
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All devices are presented in the RapidIO subsystem by corresponding rio_dev data
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structure. Devices form one global device list and per-network device lists
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(depending on number of available mports and networks).
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2.3 Switch
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----------
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A RapidIO switch is a special class of device that routes packets between its
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ports towards their final destination. The packet destination port within a
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switch is defined by an internal routing table. A switch is presented in the
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RapidIO subsystem by rio_dev data structure expanded by additional rio_switch
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data structure, which contains switch specific information such as copy of the
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routing table and pointers to switch specific functions.
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The RapidIO subsystem defines the format and initialization method for subsystem
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specific switch drivers that are designed to provide hardware-specific
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implementation of common switch management routines.
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2.4 Network
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-----------
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A RapidIO network is a combination of interconnected endpoint and switch devices.
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Each RapidIO network known to the system is represented by corresponding rio_net
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data structure. This structure includes lists of all devices and local master
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ports that form the same network. It also contains a pointer to the default
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master port that is used to communicate with devices within the network.
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2.5 Device Drivers
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------------------
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RapidIO device-specific drivers follow Linux Kernel Driver Model and are
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intended to support specific RapidIO devices attached to the RapidIO network.
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2.6 Subsystem Interfaces
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------------------------
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RapidIO interconnect specification defines features that may be used to provide
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one or more common service layers for all participating RapidIO devices. These
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common services may act separately from device-specific drivers or be used by
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device-specific drivers. Example of such service provider is the RIONET driver
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which implements Ethernet-over-RapidIO interface. Because only one driver can be
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registered for a device, all common RapidIO services have to be registered as
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subsystem interfaces. This allows to have multiple common services attached to
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the same device without blocking attachment of a device-specific driver.
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3. Subsystem Initialization
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===========================
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In order to initialize the RapidIO subsystem, a platform must initialize and
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register at least one master port within the RapidIO network. To register mport
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within the subsystem controller driver's initialization code calls function
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rio_register_mport() for each available master port.
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After all active master ports are registered with a RapidIO subsystem,
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an enumeration and/or discovery routine may be called automatically or
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by user-space command.
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RapidIO subsystem can be configured to be built as a statically linked or
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modular component of the kernel (see details below).
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4. Enumeration and Discovery
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============================
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4.1 Overview
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------------
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RapidIO subsystem configuration options allow users to build enumeration and
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discovery methods as statically linked components or loadable modules.
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An enumeration/discovery method implementation and available input parameters
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define how any given method can be attached to available RapidIO mports:
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simply to all available mports OR individually to the specified mport device.
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Depending on selected enumeration/discovery build configuration, there are
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several methods to initiate an enumeration and/or discovery process:
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(a) Statically linked enumeration and discovery process can be started
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automatically during kernel initialization time using corresponding module
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parameters. This was the original method used since introduction of RapidIO
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subsystem. Now this method relies on enumerator module parameter which is
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'rio-scan.scan' for existing basic enumeration/discovery method.
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When automatic start of enumeration/discovery is used a user has to ensure
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that all discovering endpoints are started before the enumerating endpoint
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and are waiting for enumeration to be completed.
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Configuration option CONFIG_RAPIDIO_DISC_TIMEOUT defines time that discovering
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endpoint waits for enumeration to be completed. If the specified timeout
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expires the discovery process is terminated without obtaining RapidIO network
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information. NOTE: a timed out discovery process may be restarted later using
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a user-space command as it is described below (if the given endpoint was
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enumerated successfully).
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(b) Statically linked enumeration and discovery process can be started by
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a command from user space. This initiation method provides more flexibility
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for a system startup compared to the option (a) above. After all participating
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endpoints have been successfully booted, an enumeration process shall be
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started first by issuing a user-space command, after an enumeration is
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completed a discovery process can be started on all remaining endpoints.
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(c) Modular enumeration and discovery process can be started by a command from
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user space. After an enumeration/discovery module is loaded, a network scan
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process can be started by issuing a user-space command.
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Similar to the option (b) above, an enumerator has to be started first.
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(d) Modular enumeration and discovery process can be started by a module
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initialization routine. In this case an enumerating module shall be loaded
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first.
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When a network scan process is started it calls an enumeration or discovery
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routine depending on the configured role of a master port: host or agent.
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Enumeration is performed by a master port if it is configured as a host port by
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assigning a host destination ID greater than or equal to zero. The host
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destination ID can be assigned to a master port using various methods depending
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on RapidIO subsystem build configuration:
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(a) For a statically linked RapidIO subsystem core use command line parameter
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"rapidio.hdid=" with a list of destination ID assignments in order of mport
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device registration. For example, in a system with two RapidIO controllers
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the command line parameter "rapidio.hdid=-1,7" will result in assignment of
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the host destination ID=7 to the second RapidIO controller, while the first
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one will be assigned destination ID=-1.
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(b) If the RapidIO subsystem core is built as a loadable module, in addition
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to the method shown above, the host destination ID(s) can be specified using
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traditional methods of passing module parameter "hdid=" during its loading:
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- from command line: "modprobe rapidio hdid=-1,7", or
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- from modprobe configuration file using configuration command "options",
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like in this example: "options rapidio hdid=-1,7". An example of modprobe
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configuration file is provided in the section below.
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NOTES:
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(i) if "hdid=" parameter is omitted all available mport will be assigned
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destination ID = -1;
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(ii) the "hdid=" parameter in systems with multiple mports can have
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destination ID assignments omitted from the end of list (default = -1).
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If the host device ID for a specific master port is set to -1, the discovery
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process will be performed for it.
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The enumeration and discovery routines use RapidIO maintenance transactions
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to access the configuration space of devices.
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NOTE: If RapidIO switch-specific device drivers are built as loadable modules
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they must be loaded before enumeration/discovery process starts.
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This requirement is cased by the fact that enumeration/discovery methods invoke
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vendor-specific callbacks on early stages.
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4.2 Automatic Start of Enumeration and Discovery
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------------------------------------------------
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Automatic enumeration/discovery start method is applicable only to built-in
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enumeration/discovery RapidIO configuration selection. To enable automatic
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enumeration/discovery start by existing basic enumerator method set use boot
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command line parameter "rio-scan.scan=1".
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This configuration requires synchronized start of all RapidIO endpoints that
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form a network which will be enumerated/discovered. Discovering endpoints have
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to be started before an enumeration starts to ensure that all RapidIO
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controllers have been initialized and are ready to be discovered. Configuration
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parameter CONFIG_RAPIDIO_DISC_TIMEOUT defines time (in seconds) which
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a discovering endpoint will wait for enumeration to be completed.
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When automatic enumeration/discovery start is selected, basic method's
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initialization routine calls rio_init_mports() to perform enumeration or
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discovery for all known mport devices.
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Depending on RapidIO network size and configuration this automatic
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enumeration/discovery start method may be difficult to use due to the
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requirement for synchronized start of all endpoints.
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4.3 User-space Start of Enumeration and Discovery
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-------------------------------------------------
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User-space start of enumeration and discovery can be used with built-in and
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modular build configurations. For user-space controlled start RapidIO subsystem
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creates the sysfs write-only attribute file '/sys/bus/rapidio/scan'. To initiate
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an enumeration or discovery process on specific mport device, a user needs to
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write mport_ID (not RapidIO destination ID) into that file. The mport_ID is a
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sequential number (0 ... RIO_MAX_MPORTS) assigned during mport device
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registration. For example for machine with single RapidIO controller, mport_ID
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for that controller always will be 0.
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To initiate RapidIO enumeration/discovery on all available mports a user may
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write '-1' (or RIO_MPORT_ANY) into the scan attribute file.
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4.4 Basic Enumeration Method
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----------------------------
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This is an original enumeration/discovery method which is available since
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first release of RapidIO subsystem code. The enumeration process is
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implemented according to the enumeration algorithm outlined in the RapidIO
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Interconnect Specification: Annex I [1].
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This method can be configured as statically linked or loadable module.
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The method's single parameter "scan" allows to trigger the enumeration/discovery
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process from module initialization routine.
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This enumeration/discovery method can be started only once and does not support
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unloading if it is built as a module.
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The enumeration process traverses the network using a recursive depth-first
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algorithm. When a new device is found, the enumerator takes ownership of that
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device by writing into the Host Device ID Lock CSR. It does this to ensure that
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the enumerator has exclusive right to enumerate the device. If device ownership
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is successfully acquired, the enumerator allocates a new rio_dev structure and
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initializes it according to device capabilities.
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If the device is an endpoint, a unique device ID is assigned to it and its value
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is written into the device's Base Device ID CSR.
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If the device is a switch, the enumerator allocates an additional rio_switch
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structure to store switch specific information. Then the switch's vendor ID and
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device ID are queried against a table of known RapidIO switches. Each switch
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table entry contains a pointer to a switch-specific initialization routine that
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initializes pointers to the rest of switch specific operations, and performs
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hardware initialization if necessary. A RapidIO switch does not have a unique
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device ID; it relies on hopcount and routing for device ID of an attached
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endpoint if access to its configuration registers is required. If a switch (or
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chain of switches) does not have any endpoint (except enumerator) attached to
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it, a fake device ID will be assigned to configure a route to that switch.
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In the case of a chain of switches without endpoint, one fake device ID is used
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to configure a route through the entire chain and switches are differentiated by
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their hopcount value.
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For both endpoints and switches the enumerator writes a unique component tag
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into device's Component Tag CSR. That unique value is used by the error
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management notification mechanism to identify a device that is reporting an
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error management event.
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Enumeration beyond a switch is completed by iterating over each active egress
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port of that switch. For each active link, a route to a default device ID
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(0xFF for 8-bit systems and 0xFFFF for 16-bit systems) is temporarily written
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into the routing table. The algorithm recurs by calling itself with hopcount + 1
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and the default device ID in order to access the device on the active port.
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After the host has completed enumeration of the entire network it releases
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devices by clearing device ID locks (calls rio_clear_locks()). For each endpoint
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in the system, it sets the Discovered bit in the Port General Control CSR
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to indicate that enumeration is completed and agents are allowed to execute
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passive discovery of the network.
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The discovery process is performed by agents and is similar to the enumeration
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process that is described above. However, the discovery process is performed
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without changes to the existing routing because agents only gather information
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about RapidIO network structure and are building an internal map of discovered
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devices. This way each Linux-based component of the RapidIO subsystem has
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a complete view of the network. The discovery process can be performed
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simultaneously by several agents. After initializing its RapidIO master port
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each agent waits for enumeration completion by the host for the configured wait
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time period. If this wait time period expires before enumeration is completed,
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an agent skips RapidIO discovery and continues with remaining kernel
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initialization.
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4.5 Adding New Enumeration/Discovery Method
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-------------------------------------------
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RapidIO subsystem code organization allows addition of new enumeration/discovery
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methods as new configuration options without significant impact to the core
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RapidIO code.
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A new enumeration/discovery method has to be attached to one or more mport
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devices before an enumeration/discovery process can be started. Normally,
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method's module initialization routine calls rio_register_scan() to attach
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an enumerator to a specified mport device (or devices). The basic enumerator
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implementation demonstrates this process.
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4.6 Using Loadable RapidIO Switch Drivers
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-----------------------------------------
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In the case when RapidIO switch drivers are built as loadable modules a user
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must ensure that they are loaded before the enumeration/discovery starts.
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This process can be automated by specifying pre- or post- dependencies in the
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RapidIO-specific modprobe configuration file as shown in the example below.
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File /etc/modprobe.d/rapidio.conf::
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# Configure RapidIO subsystem modules
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# Set enumerator host destination ID (overrides kernel command line option)
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options rapidio hdid=-1,2
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# Load RapidIO switch drivers immediately after rapidio core module was loaded
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softdep rapidio post: idt_gen2 idtcps tsi57x
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# OR :
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# Load RapidIO switch drivers just before rio-scan enumerator module is loaded
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softdep rio-scan pre: idt_gen2 idtcps tsi57x
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--------------------------
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NOTE:
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In the example above, one of "softdep" commands must be removed or
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commented out to keep required module loading sequence.
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5. References
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=============
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[1] RapidIO Trade Association. RapidIO Interconnect Specifications.
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http://www.rapidio.org.
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[2] Rapidio TA. Technology Comparisons.
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http://www.rapidio.org/education/technology_comparisons/
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[3] RapidIO support for Linux.
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http://lwn.net/Articles/139118/
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[4] Matt Porter. RapidIO for Linux. Ottawa Linux Symposium, 2005
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http://www.kernel.org/doc/ols/2005/ols2005v2-pages-43-56.pdf
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