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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.
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.
A. 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

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RapidIO sysfs Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. RapidIO Device Subdirectories
--------------------------------
For each RapidIO device, the RapidIO subsystem creates files in an individual
subdirectory with the following name, /sys/bus/rapidio/devices/<device_name>.
The format of device_name is "nn:d:iiii", where:
nn - two-digit hexadecimal ID of RapidIO network where the device resides
d - device typr: 'e' - for endpoint or 's' - for switch
iiii - four-digit device destID for endpoints, or switchID for switches
For example, below is a list of device directories that represents a typical
RapidIO network with one switch, one host, and two agent endpoints, as it is
seen by the enumerating host (destID = 1):
/sys/bus/rapidio/devices/00:e:0000
/sys/bus/rapidio/devices/00:e:0002
/sys/bus/rapidio/devices/00:s:0001
NOTE: An enumerating or discovering endpoint does not create a sysfs entry for
itself, this is why an endpoint with destID=1 is not shown in the list.
2. Attributes Common for All RapidIO Devices
--------------------------------------------
Each device subdirectory contains the following informational read-only files:
did - returns the device identifier
vid - returns the device vendor identifier
device_rev - returns the device revision level
asm_did - returns identifier for the assembly containing the device
asm_rev - returns revision level of the assembly containing the device
asm_vid - returns vendor identifier of the assembly containing the device
destid - returns device destination ID assigned by the enumeration routine
(see 4.1 for switch specific details)
lprev - returns name of previous device (switch) on the path to the device
that that owns this attribute
modalias - returns the device modalias
In addition to the files listed above, each device has a binary attribute file
that allows read/write access to the device configuration registers using
the RapidIO maintenance transactions:
config - reads from and writes to the device configuration registers.
This attribute is similar in behavior to the "config" attribute of PCI devices
and provides an access to the RapidIO device registers using standard file read
and write operations.
3. RapidIO Endpoint Device Attributes
-------------------------------------
Currently Linux RapidIO subsystem does not create any endpoint specific sysfs
attributes. It is possible that RapidIO master port drivers and endpoint device
drivers will add their device-specific sysfs attributes but such attributes are
outside the scope of this document.
4. RapidIO Switch Device Attributes
-----------------------------------
RapidIO switches have additional attributes in sysfs. RapidIO subsystem supports
common and device-specific sysfs attributes for switches. Because switches are
integrated into the RapidIO subsystem, it offers a method to create
device-specific sysfs attributes by specifying a callback function that may be
set by the switch initialization routine during enumeration or discovery process.
4.1 Common Switch Attributes
routes - reports switch routing information in "destID port" format. This
attribute reports only valid routing table entries, one line for
each entry.
destid - device destination ID that defines a route to the switch
hopcount - number of hops on the path to the switch
lnext - returns names of devices linked to the switch except one of a device
linked to the ingress port (reported as "lprev"). This is an array
names with number of lines equal to number of ports in switch. If
a switch port has no attached device, returns "null" instead of
a device name.
4.2 Device-specific Switch Attributes
Device-specific switch attributes are listed for each RapidIO switch driver
that exports additional attributes.
IDT_GEN2:
errlog - reads contents of device error log until it is empty.
5. RapidIO Bus Attributes
-------------------------
RapidIO bus subdirectory /sys/bus/rapidio implements the following bus-specific
attribute:
scan - allows to trigger enumeration discovery process from user space. This
is a write-only attribute. To initiate an enumeration or discovery
process on specific mport device, a user needs to write mport_ID (not
RapidIO destination ID) into this file. The mport_ID is a sequential
number (0 ... RIO_MAX_MPORTS) assigned to the mport device.
For example, for a machine with a single RapidIO controller, mport_ID
for that controller always will be 0.
To initiate RapidIO enumeration/discovery on all available mports
a user must write '-1' (or RIO_MPORT_ANY) into this attribute file.
6. RapidIO Bus Controllers/Ports
--------------------------------
On-chip RapidIO controllers and PCIe-to-RapidIO bridges (referenced as
"Master Port" or "mport") are presented in sysfs as the special class of
devices: "rapidio_port".
The /sys/class/rapidio_port subdirectory contains individual subdirectories
named as "rapidioN" where N = mport ID registered with RapidIO subsystem.
NOTE: An mport ID is not a RapidIO destination ID assigned to a given local
mport device.
Each mport device subdirectory in addition to standard entries contains the
following device-specific attributes:
port_destid - reports RapidIO destination ID assigned to the given RapidIO
mport device. If value 0xFFFFFFFF is returned this means that
no valid destination ID have been assigned to the mport (yet).
Normally, before enumeration/discovery have been executed only
fabric enumerating mports have a valid destination ID assigned
to them using "hdid=..." rapidio module parameter.
sys_size - reports RapidIO common transport system size:
0 = small (8-bit destination ID, max. 256 devices),
1 = large (16-bit destination ID, max. 65536 devices).
After enumeration or discovery was performed for a given mport device,
the corresponding subdirectory will also contain subdirectories for each
child RapidIO device connected to the mport. Naming conventions for RapidIO
devices are described in Section 1 above.
The example below shows mport device subdirectory with several child RapidIO
devices attached to it.
[rio@rapidio ~]$ ls /sys/class/rapidio_port/rapidio0/ -l
total 0
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:e:0001
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:e:0004
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:e:0007
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:s:0002
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:s:0003
drwxr-xr-x 3 root root 0 Feb 11 15:10 00:s:0005
lrwxrwxrwx 1 root root 0 Feb 11 15:11 device -> ../../../0000:01:00.0
-r--r--r-- 1 root root 4096 Feb 11 15:11 port_destid
drwxr-xr-x 2 root root 0 Feb 11 15:11 power
lrwxrwxrwx 1 root root 0 Feb 11 15:04 subsystem -> ../../../../../../class/rapidio_port
-r--r--r-- 1 root root 4096 Feb 11 15:11 sys_size
-rw-r--r-- 1 root root 4096 Feb 11 15:04 uevent

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RapidIO subsystem mport driver for IDT Tsi721 PCI Express-to-SRIO bridge.
=========================================================================
I. Overview
This driver implements all currently defined RapidIO mport callback functions.
It supports maintenance read and write operations, inbound and outbound RapidIO
doorbells, inbound maintenance port-writes and RapidIO messaging.
To generate SRIO maintenance transactions this driver uses one of Tsi721 DMA
channels. This mechanism provides access to larger range of hop counts and
destination IDs without need for changes in outbound window translation.
RapidIO messaging support uses dedicated messaging channels for each mailbox.
For inbound messages this driver uses destination ID matching to forward messages
into the corresponding message queue. Messaging callbacks are implemented to be
fully compatible with RIONET driver (Ethernet over RapidIO messaging services).
II. Known problems
None.
III. DMA Engine Support
Tsi721 mport driver supports DMA data transfers between local system memory and
remote RapidIO devices. This functionality is implemented according to SLAVE
mode API defined by common Linux kernel DMA Engine framework.
Depending on system requirements RapidIO DMA operations can be included/excluded
by setting CONFIG_RAPIDIO_DMA_ENGINE option. Tsi721 miniport driver uses seven
out of eight available BDMA channels to support DMA data transfers.
One BDMA channel is reserved for generation of maintenance read/write requests.
If Tsi721 mport driver have been built with RAPIDIO_DMA_ENGINE support included,
this driver will accept DMA-specific module parameter:
"dma_desc_per_channel" - defines number of hardware buffer descriptors used by
each BDMA channel of Tsi721 (by default - 128).
IV. Version History
1.1.0 - DMA operations re-worked to support data scatter/gather lists larger
than hardware buffer descriptors ring.
1.0.0 - Initial driver release.
V. License
-----------------------------------------------
Copyright(c) 2011 Integrated Device Technology, Inc. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option)
any later version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.