Based on kernel version 3.9. Page generated on 2013-05-02 23:12 EST.
1 The Linux RapidIO Subsystem 2 3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 5 The RapidIO standard is a packet-based fabric interconnect standard designed for 6 use in embedded systems. Development of the RapidIO standard is directed by the 7 RapidIO Trade Association (RTA). The current version of the RapidIO specification 8 is publicly available for download from the RTA web-site . 9 10 This document describes the basics of the Linux RapidIO subsystem and provides 11 information on its major components. 12 13 1 Overview 14 ---------- 15 16 Because the RapidIO subsystem follows the Linux device model it is integrated 17 into the kernel similarly to other buses by defining RapidIO-specific device and 18 bus types and registering them within the device model. 19 20 The Linux RapidIO subsystem is architecture independent and therefore defines 21 architecture-specific interfaces that provide support for common RapidIO 22 subsystem operations. 23 24 2. Core Components 25 ------------------ 26 27 A typical RapidIO network is a combination of endpoints and switches. 28 Each of these components is represented in the subsystem by an associated data 29 structure. The core logical components of the RapidIO subsystem are defined 30 in include/linux/rio.h file. 31 32 2.1 Master Port 33 34 A master port (or mport) is a RapidIO interface controller that is local to the 35 processor executing the Linux code. A master port generates and receives RapidIO 36 packets (transactions). In the RapidIO subsystem each master port is represented 37 by a rio_mport data structure. This structure contains master port specific 38 resources such as mailboxes and doorbells. The rio_mport also includes a unique 39 host device ID that is valid when a master port is configured as an enumerating 40 host. 41 42 RapidIO master ports are serviced by subsystem specific mport device drivers 43 that provide functionality defined for this subsystem. To provide a hardware 44 independent interface for RapidIO subsystem operations, rio_mport structure 45 includes rio_ops data structure which contains pointers to hardware specific 46 implementations of RapidIO functions. 47 48 2.2 Device 49 50 A RapidIO device is any endpoint (other than mport) or switch in the network. 51 All devices are presented in the RapidIO subsystem by corresponding rio_dev data 52 structure. Devices form one global device list and per-network device lists 53 (depending on number of available mports and networks). 54 55 2.3 Switch 56 57 A RapidIO switch is a special class of device that routes packets between its 58 ports towards their final destination. The packet destination port within a 59 switch is defined by an internal routing table. A switch is presented in the 60 RapidIO subsystem by rio_dev data structure expanded by additional rio_switch 61 data structure, which contains switch specific information such as copy of the 62 routing table and pointers to switch specific functions. 63 64 The RapidIO subsystem defines the format and initialization method for subsystem 65 specific switch drivers that are designed to provide hardware-specific 66 implementation of common switch management routines. 67 68 2.4 Network 69 70 A RapidIO network is a combination of interconnected endpoint and switch devices. 71 Each RapidIO network known to the system is represented by corresponding rio_net 72 data structure. This structure includes lists of all devices and local master 73 ports that form the same network. It also contains a pointer to the default 74 master port that is used to communicate with devices within the network. 75 76 3. Subsystem Initialization 77 --------------------------- 78 79 In order to initialize the RapidIO subsystem, a platform must initialize and 80 register at least one master port within the RapidIO network. To register mport 81 within the subsystem controller driver initialization code calls function 82 rio_register_mport() for each available master port. After all active master 83 ports are registered with a RapidIO subsystem, the rio_init_mports() routine 84 is called to perform enumeration and discovery. 85 86 In the current PowerPC-based implementation a subsys_initcall() is specified to 87 perform controller initialization and mport registration. At the end it directly 88 calls rio_init_mports() to execute RapidIO enumeration and discovery. 89 90 4. Enumeration and Discovery 91 ---------------------------- 92 93 When rio_init_mports() is called it scans a list of registered master ports and 94 calls an enumeration or discovery routine depending on the configured role of a 95 master port: host or agent. 96 97 Enumeration is performed by a master port if it is configured as a host port by 98 assigning a host device ID greater than or equal to zero. A host device ID is 99 assigned to a master port through the kernel command line parameter "riohdid=", 100 or can be configured in a platform-specific manner. If the host device ID for 101 a specific master port is set to -1, the discovery process will be performed 102 for it. 103 104 The enumeration and discovery routines use RapidIO maintenance transactions 105 to access the configuration space of devices. 106 107 The enumeration process is implemented according to the enumeration algorithm 108 outlined in the RapidIO Interconnect Specification: Annex I . 109 110 The enumeration process traverses the network using a recursive depth-first 111 algorithm. When a new device is found, the enumerator takes ownership of that 112 device by writing into the Host Device ID Lock CSR. It does this to ensure that 113 the enumerator has exclusive right to enumerate the device. If device ownership 114 is successfully acquired, the enumerator allocates a new rio_dev structure and 115 initializes it according to device capabilities. 116 117 If the device is an endpoint, a unique device ID is assigned to it and its value 118 is written into the device's Base Device ID CSR. 119 120 If the device is a switch, the enumerator allocates an additional rio_switch 121 structure to store switch specific information. Then the switch's vendor ID and 122 device ID are queried against a table of known RapidIO switches. Each switch 123 table entry contains a pointer to a switch-specific initialization routine that 124 initializes pointers to the rest of switch specific operations, and performs 125 hardware initialization if necessary. A RapidIO switch does not have a unique 126 device ID; it relies on hopcount and routing for device ID of an attached 127 endpoint if access to its configuration registers is required. If a switch (or 128 chain of switches) does not have any endpoint (except enumerator) attached to 129 it, a fake device ID will be assigned to configure a route to that switch. 130 In the case of a chain of switches without endpoint, one fake device ID is used 131 to configure a route through the entire chain and switches are differentiated by 132 their hopcount value. 133 134 For both endpoints and switches the enumerator writes a unique component tag 135 into device's Component Tag CSR. That unique value is used by the error 136 management notification mechanism to identify a device that is reporting an 137 error management event. 138 139 Enumeration beyond a switch is completed by iterating over each active egress 140 port 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 142 into the routing table. The algorithm recurs by calling itself with hopcount + 1 143 and the default device ID in order to access the device on the active port. 144 145 After the host has completed enumeration of the entire network it releases 146 devices by clearing device ID locks (calls rio_clear_locks()). For each endpoint 147 in the system, it sets the Discovered bit in the Port General Control CSR 148 to indicate that enumeration is completed and agents are allowed to execute 149 passive discovery of the network. 150 151 The discovery process is performed by agents and is similar to the enumeration 152 process that is described above. However, the discovery process is performed 153 without changes to the existing routing because agents only gather information 154 about RapidIO network structure and are building an internal map of discovered 155 devices. This way each Linux-based component of the RapidIO subsystem has 156 a complete view of the network. The discovery process can be performed 157 simultaneously by several agents. After initializing its RapidIO master port 158 each agent waits for enumeration completion by the host for the configured wait 159 time period. If this wait time period expires before enumeration is completed, 160 an agent skips RapidIO discovery and continues with remaining kernel 161 initialization. 162 163 5. References 164 ------------- 165 166  RapidIO Trade Association. RapidIO Interconnect Specifications. 167 http://www.rapidio.org. 168  Rapidio TA. Technology Comparisons. 169 http://www.rapidio.org/education/technology_comparisons/ 170  RapidIO support for Linux. 171 http://lwn.net/Articles/139118/ 172  Matt Porter. RapidIO for Linux. Ottawa Linux Symposium, 2005 173 http://www.kernel.org/doc/ols/2005/ols2005v2-pages-43-56.pdf