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