Documentation/rapidio/rapidio.txt - kernel/mindspeed - Git at Google

                           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
	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