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diff --git a/Documentation/rapidio/rapidio.txt b/Documentation/rapidio/rapidio.txt new file mode 100644 index 00000000000..be70ee15f8c --- /dev/null +++ b/Documentation/rapidio/rapidio.txt @@ -0,0 +1,173 @@ + 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 Master Enable 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 |