363 lines
17 KiB
ReStructuredText
363 lines
17 KiB
ReStructuredText
============
|
|
Introduction
|
|
============
|
|
|
|
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.
|
|
|
|
2.5 Device Drivers
|
|
------------------
|
|
|
|
RapidIO device-specific drivers follow Linux Kernel Driver Model and are
|
|
intended to support specific RapidIO devices attached to the RapidIO network.
|
|
|
|
2.6 Subsystem Interfaces
|
|
------------------------
|
|
|
|
RapidIO interconnect specification defines features that may be used to provide
|
|
one or more common service layers for all participating RapidIO devices. These
|
|
common services may act separately from device-specific drivers or be used by
|
|
device-specific drivers. Example of such service provider is the RIONET driver
|
|
which implements Ethernet-over-RapidIO interface. Because only one driver can be
|
|
registered for a device, all common RapidIO services have to be registered as
|
|
subsystem interfaces. This allows to have multiple common services attached to
|
|
the same device without blocking attachment of a device-specific driver.
|
|
|
|
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's initialization code calls function
|
|
rio_register_mport() for each available master port.
|
|
|
|
After all active master ports are registered with a RapidIO subsystem,
|
|
an enumeration and/or discovery routine may be called automatically or
|
|
by user-space command.
|
|
|
|
RapidIO subsystem can be configured to be built as a statically linked or
|
|
modular component of the kernel (see details below).
|
|
|
|
4. Enumeration and Discovery
|
|
============================
|
|
|
|
4.1 Overview
|
|
------------
|
|
|
|
RapidIO subsystem configuration options allow users to build enumeration and
|
|
discovery methods as statically linked components or loadable modules.
|
|
An enumeration/discovery method implementation and available input parameters
|
|
define how any given method can be attached to available RapidIO mports:
|
|
simply to all available mports OR individually to the specified mport device.
|
|
|
|
Depending on selected enumeration/discovery build configuration, there are
|
|
several methods to initiate an enumeration and/or discovery process:
|
|
|
|
(a) Statically linked enumeration and discovery process can be started
|
|
automatically during kernel initialization time using corresponding module
|
|
parameters. This was the original method used since introduction of RapidIO
|
|
subsystem. Now this method relies on enumerator module parameter which is
|
|
'rio-scan.scan' for existing basic enumeration/discovery method.
|
|
When automatic start of enumeration/discovery is used a user has to ensure
|
|
that all discovering endpoints are started before the enumerating endpoint
|
|
and are waiting for enumeration to be completed.
|
|
Configuration option CONFIG_RAPIDIO_DISC_TIMEOUT defines time that discovering
|
|
endpoint waits for enumeration to be completed. If the specified timeout
|
|
expires the discovery process is terminated without obtaining RapidIO network
|
|
information. NOTE: a timed out discovery process may be restarted later using
|
|
a user-space command as it is described below (if the given endpoint was
|
|
enumerated successfully).
|
|
|
|
(b) Statically linked enumeration and discovery process can be started by
|
|
a command from user space. This initiation method provides more flexibility
|
|
for a system startup compared to the option (a) above. After all participating
|
|
endpoints have been successfully booted, an enumeration process shall be
|
|
started first by issuing a user-space command, after an enumeration is
|
|
completed a discovery process can be started on all remaining endpoints.
|
|
|
|
(c) Modular enumeration and discovery process can be started by a command from
|
|
user space. After an enumeration/discovery module is loaded, a network scan
|
|
process can be started by issuing a user-space command.
|
|
Similar to the option (b) above, an enumerator has to be started first.
|
|
|
|
(d) Modular enumeration and discovery process can be started by a module
|
|
initialization routine. In this case an enumerating module shall be loaded
|
|
first.
|
|
|
|
When a network scan process is started it 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 destination ID greater than or equal to zero. The host
|
|
destination ID can be assigned to a master port using various methods depending
|
|
on RapidIO subsystem build configuration:
|
|
|
|
(a) For a statically linked RapidIO subsystem core use command line parameter
|
|
"rapidio.hdid=" with a list of destination ID assignments in order of mport
|
|
device registration. For example, in a system with two RapidIO controllers
|
|
the command line parameter "rapidio.hdid=-1,7" will result in assignment of
|
|
the host destination ID=7 to the second RapidIO controller, while the first
|
|
one will be assigned destination ID=-1.
|
|
|
|
(b) If the RapidIO subsystem core is built as a loadable module, in addition
|
|
to the method shown above, the host destination ID(s) can be specified using
|
|
traditional methods of passing module parameter "hdid=" during its loading:
|
|
|
|
- from command line: "modprobe rapidio hdid=-1,7", or
|
|
- from modprobe configuration file using configuration command "options",
|
|
like in this example: "options rapidio hdid=-1,7". An example of modprobe
|
|
configuration file is provided in the section below.
|
|
|
|
NOTES:
|
|
(i) if "hdid=" parameter is omitted all available mport will be assigned
|
|
destination ID = -1;
|
|
|
|
(ii) the "hdid=" parameter in systems with multiple mports can have
|
|
destination ID assignments omitted from the end of list (default = -1).
|
|
|
|
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.
|
|
|
|
NOTE: If RapidIO switch-specific device drivers are built as loadable modules
|
|
they must be loaded before enumeration/discovery process starts.
|
|
This requirement is cased by the fact that enumeration/discovery methods invoke
|
|
vendor-specific callbacks on early stages.
|
|
|
|
4.2 Automatic Start of Enumeration and Discovery
|
|
------------------------------------------------
|
|
|
|
Automatic enumeration/discovery start method is applicable only to built-in
|
|
enumeration/discovery RapidIO configuration selection. To enable automatic
|
|
enumeration/discovery start by existing basic enumerator method set use boot
|
|
command line parameter "rio-scan.scan=1".
|
|
|
|
This configuration requires synchronized start of all RapidIO endpoints that
|
|
form a network which will be enumerated/discovered. Discovering endpoints have
|
|
to be started before an enumeration starts to ensure that all RapidIO
|
|
controllers have been initialized and are ready to be discovered. Configuration
|
|
parameter CONFIG_RAPIDIO_DISC_TIMEOUT defines time (in seconds) which
|
|
a discovering endpoint will wait for enumeration to be completed.
|
|
|
|
When automatic enumeration/discovery start is selected, basic method's
|
|
initialization routine calls rio_init_mports() to perform enumeration or
|
|
discovery for all known mport devices.
|
|
|
|
Depending on RapidIO network size and configuration this automatic
|
|
enumeration/discovery start method may be difficult to use due to the
|
|
requirement for synchronized start of all endpoints.
|
|
|
|
4.3 User-space Start of Enumeration and Discovery
|
|
-------------------------------------------------
|
|
|
|
User-space start of enumeration and discovery can be used with built-in and
|
|
modular build configurations. For user-space controlled start RapidIO subsystem
|
|
creates the sysfs write-only attribute file '/sys/bus/rapidio/scan'. To initiate
|
|
an enumeration or discovery process on specific mport device, a user needs to
|
|
write mport_ID (not RapidIO destination ID) into that file. The mport_ID is a
|
|
sequential number (0 ... RIO_MAX_MPORTS) assigned during mport device
|
|
registration. For example for machine with single RapidIO controller, mport_ID
|
|
for that controller always will be 0.
|
|
|
|
To initiate RapidIO enumeration/discovery on all available mports a user may
|
|
write '-1' (or RIO_MPORT_ANY) into the scan attribute file.
|
|
|
|
4.4 Basic Enumeration Method
|
|
----------------------------
|
|
|
|
This is an original enumeration/discovery method which is available since
|
|
first release of RapidIO subsystem code. The enumeration process is
|
|
implemented according to the enumeration algorithm outlined in the RapidIO
|
|
Interconnect Specification: Annex I [1].
|
|
|
|
This method can be configured as statically linked or loadable module.
|
|
The method's single parameter "scan" allows to trigger the enumeration/discovery
|
|
process from module initialization routine.
|
|
|
|
This enumeration/discovery method can be started only once and does not support
|
|
unloading if it is built as a module.
|
|
|
|
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.
|
|
|
|
4.5 Adding New Enumeration/Discovery Method
|
|
-------------------------------------------
|
|
|
|
RapidIO subsystem code organization allows addition of new enumeration/discovery
|
|
methods as new configuration options without significant impact to the core
|
|
RapidIO code.
|
|
|
|
A new enumeration/discovery method has to be attached to one or more mport
|
|
devices before an enumeration/discovery process can be started. Normally,
|
|
method's module initialization routine calls rio_register_scan() to attach
|
|
an enumerator to a specified mport device (or devices). The basic enumerator
|
|
implementation demonstrates this process.
|
|
|
|
4.6 Using Loadable RapidIO Switch Drivers
|
|
-----------------------------------------
|
|
|
|
In the case when RapidIO switch drivers are built as loadable modules a user
|
|
must ensure that they are loaded before the enumeration/discovery starts.
|
|
This process can be automated by specifying pre- or post- dependencies in the
|
|
RapidIO-specific modprobe configuration file as shown in the example below.
|
|
|
|
File /etc/modprobe.d/rapidio.conf::
|
|
|
|
# Configure RapidIO subsystem modules
|
|
|
|
# Set enumerator host destination ID (overrides kernel command line option)
|
|
options rapidio hdid=-1,2
|
|
|
|
# Load RapidIO switch drivers immediately after rapidio core module was loaded
|
|
softdep rapidio post: idt_gen2 idtcps tsi57x
|
|
|
|
# OR :
|
|
|
|
# Load RapidIO switch drivers just before rio-scan enumerator module is loaded
|
|
softdep rio-scan pre: idt_gen2 idtcps tsi57x
|
|
|
|
--------------------------
|
|
|
|
NOTE:
|
|
In the example above, one of "softdep" commands must be removed or
|
|
commented out to keep required module loading sequence.
|
|
|
|
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.
|
|
https://lwn.net/Articles/139118/
|
|
|
|
[4] Matt Porter. RapidIO for Linux. Ottawa Linux Symposium, 2005
|
|
https://www.kernel.org/doc/ols/2005/ols2005v2-pages-43-56.pdf
|