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Alexandre Bouninee15b4d62011-03-23 16:43:00 -07001 The Linux RapidIO Subsystem
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4
5The RapidIO standard is a packet-based fabric interconnect standard designed for
6use in embedded systems. Development of the RapidIO standard is directed by the
7RapidIO Trade Association (RTA). The current version of the RapidIO specification
8is publicly available for download from the RTA web-site [1].
9
10This document describes the basics of the Linux RapidIO subsystem and provides
11information on its major components.
12
131 Overview
14----------
15
16Because the RapidIO subsystem follows the Linux device model it is integrated
17into the kernel similarly to other buses by defining RapidIO-specific device and
18bus types and registering them within the device model.
19
20The Linux RapidIO subsystem is architecture independent and therefore defines
21architecture-specific interfaces that provide support for common RapidIO
22subsystem operations.
23
242. Core Components
25------------------
26
27A typical RapidIO network is a combination of endpoints and switches.
28Each of these components is represented in the subsystem by an associated data
29structure. The core logical components of the RapidIO subsystem are defined
30in include/linux/rio.h file.
31
322.1 Master Port
33
34A master port (or mport) is a RapidIO interface controller that is local to the
35processor executing the Linux code. A master port generates and receives RapidIO
36packets (transactions). In the RapidIO subsystem each master port is represented
37by a rio_mport data structure. This structure contains master port specific
38resources such as mailboxes and doorbells. The rio_mport also includes a unique
39host device ID that is valid when a master port is configured as an enumerating
40host.
41
42RapidIO master ports are serviced by subsystem specific mport device drivers
43that provide functionality defined for this subsystem. To provide a hardware
44independent interface for RapidIO subsystem operations, rio_mport structure
45includes rio_ops data structure which contains pointers to hardware specific
46implementations of RapidIO functions.
47
482.2 Device
49
50A RapidIO device is any endpoint (other than mport) or switch in the network.
51All devices are presented in the RapidIO subsystem by corresponding rio_dev data
52structure. Devices form one global device list and per-network device lists
53(depending on number of available mports and networks).
54
552.3 Switch
56
57A RapidIO switch is a special class of device that routes packets between its
58ports towards their final destination. The packet destination port within a
59switch is defined by an internal routing table. A switch is presented in the
60RapidIO subsystem by rio_dev data structure expanded by additional rio_switch
61data structure, which contains switch specific information such as copy of the
62routing table and pointers to switch specific functions.
63
64The RapidIO subsystem defines the format and initialization method for subsystem
65specific switch drivers that are designed to provide hardware-specific
66implementation of common switch management routines.
67
682.4 Network
69
70A RapidIO network is a combination of interconnected endpoint and switch devices.
71Each RapidIO network known to the system is represented by corresponding rio_net
72data structure. This structure includes lists of all devices and local master
73ports that form the same network. It also contains a pointer to the default
74master port that is used to communicate with devices within the network.
75
763. Subsystem Initialization
77---------------------------
78
79In order to initialize the RapidIO subsystem, a platform must initialize and
80register at least one master port within the RapidIO network. To register mport
81within the subsystem controller driver initialization code calls function
82rio_register_mport() for each available master port. After all active master
83ports are registered with a RapidIO subsystem, the rio_init_mports() routine
84is called to perform enumeration and discovery.
85
86In the current PowerPC-based implementation a subsys_initcall() is specified to
87perform controller initialization and mport registration. At the end it directly
88calls rio_init_mports() to execute RapidIO enumeration and discovery.
89
904. Enumeration and Discovery
91----------------------------
92
93When rio_init_mports() is called it scans a list of registered master ports and
94calls an enumeration or discovery routine depending on the configured role of a
95master port: host or agent.
96
97Enumeration is performed by a master port if it is configured as a host port by
98assigning a host device ID greater than or equal to zero. A host device ID is
99assigned to a master port through the kernel command line parameter "riohdid=",
100or can be configured in a platform-specific manner. If the host device ID for
101a specific master port is set to -1, the discovery process will be performed
102for it.
103
104The enumeration and discovery routines use RapidIO maintenance transactions
105to access the configuration space of devices.
106
107The enumeration process is implemented according to the enumeration algorithm
108outlined in the RapidIO Interconnect Specification: Annex I [1].
109
110The enumeration process traverses the network using a recursive depth-first
111algorithm. When a new device is found, the enumerator takes ownership of that
112device by writing into the Host Device ID Lock CSR. It does this to ensure that
113the enumerator has exclusive right to enumerate the device. If device ownership
114is successfully acquired, the enumerator allocates a new rio_dev structure and
115initializes it according to device capabilities.
116
117If the device is an endpoint, a unique device ID is assigned to it and its value
118is written into the device's Base Device ID CSR.
119
120If the device is a switch, the enumerator allocates an additional rio_switch
121structure to store switch specific information. Then the switch's vendor ID and
122device ID are queried against a table of known RapidIO switches. Each switch
123table entry contains a pointer to a switch-specific initialization routine that
124initializes pointers to the rest of switch specific operations, and performs
125hardware initialization if necessary. A RapidIO switch does not have a unique
126device ID; it relies on hopcount and routing for device ID of an attached
127endpoint if access to its configuration registers is required. If a switch (or
128chain of switches) does not have any endpoint (except enumerator) attached to
129it, a fake device ID will be assigned to configure a route to that switch.
130In the case of a chain of switches without endpoint, one fake device ID is used
131to configure a route through the entire chain and switches are differentiated by
132their hopcount value.
133
134For both endpoints and switches the enumerator writes a unique component tag
135into device's Component Tag CSR. That unique value is used by the error
136management notification mechanism to identify a device that is reporting an
137error management event.
138
139Enumeration beyond a switch is completed by iterating over each active egress
140port of that switch. For each active link, a route to a default device ID
141(0xFF for 8-bit systems and 0xFFFF for 16-bit systems) is temporarily written
142into the routing table. The algorithm recurs by calling itself with hopcount + 1
143and the default device ID in order to access the device on the active port.
144
145After the host has completed enumeration of the entire network it releases
146devices by clearing device ID locks (calls rio_clear_locks()). For each endpoint
147in the system, it sets the Master Enable bit in the Port General Control CSR
148to indicate that enumeration is completed and agents are allowed to execute
149passive discovery of the network.
150
151The discovery process is performed by agents and is similar to the enumeration
152process that is described above. However, the discovery process is performed
153without changes to the existing routing because agents only gather information
154about RapidIO network structure and are building an internal map of discovered
155devices. This way each Linux-based component of the RapidIO subsystem has
156a complete view of the network. The discovery process can be performed
157simultaneously by several agents. After initializing its RapidIO master port
158each agent waits for enumeration completion by the host for the configured wait
159time period. If this wait time period expires before enumeration is completed,
160an agent skips RapidIO discovery and continues with remaining kernel
161initialization.
162
1635. References
164-------------
165
166[1] RapidIO Trade Association. RapidIO Interconnect Specifications.
167 http://www.rapidio.org.
168[2] Rapidio TA. Technology Comparisons.
169 http://www.rapidio.org/education/technology_comparisons/
170[3] RapidIO support for Linux.
171 http://lwn.net/Articles/139118/
172[4] Matt Porter. RapidIO for Linux. Ottawa Linux Symposium, 2005
173 http://www.kernel.org/doc/ols/2005/ols2005v2-pages-43-56.pdf