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- 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.
-
-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 initialization code calls function
-rio_register_mport() for each available master port. After all active master
-ports are registered with a RapidIO subsystem, the rio_init_mports() routine
-is called to perform enumeration and discovery.
-
-In the current PowerPC-based implementation a subsys_initcall() is specified to
-perform controller initialization and mport registration. At the end it directly
-calls rio_init_mports() to execute RapidIO enumeration and discovery.
-
-4. Enumeration and Discovery
-----------------------------
-
-When rio_init_mports() is called it scans a list of registered master ports and
-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 device ID greater than or equal to zero. A host device ID is
-assigned to a master port through the kernel command line parameter "riohdid=",
-or can be configured in a platform-specific manner. 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.
-
-The enumeration process is implemented according to the enumeration algorithm
-outlined in the RapidIO Interconnect Specification: Annex I [1].
-
-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.
-
-5. 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