mirror of https://gitee.com/openkylin/linux.git
116 lines
5.2 KiB
ReStructuredText
116 lines
5.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=====================================
|
|
Generic System Interconnect Subsystem
|
|
=====================================
|
|
|
|
Introduction
|
|
------------
|
|
|
|
This framework is designed to provide a standard kernel interface to control
|
|
the settings of the interconnects on an SoC. These settings can be throughput,
|
|
latency and priority between multiple interconnected devices or functional
|
|
blocks. This can be controlled dynamically in order to save power or provide
|
|
maximum performance.
|
|
|
|
The interconnect bus is hardware with configurable parameters, which can be
|
|
set on a data path according to the requests received from various drivers.
|
|
An example of interconnect buses are the interconnects between various
|
|
components or functional blocks in chipsets. There can be multiple interconnects
|
|
on an SoC that can be multi-tiered.
|
|
|
|
Below is a simplified diagram of a real-world SoC interconnect bus topology.
|
|
|
|
::
|
|
|
|
+----------------+ +----------------+
|
|
| HW Accelerator |--->| M NoC |<---------------+
|
|
+----------------+ +----------------+ |
|
|
| | +------------+
|
|
+-----+ +-------------+ V +------+ | |
|
|
| DDR | | +--------+ | PCIe | | |
|
|
+-----+ | | Slaves | +------+ | |
|
|
^ ^ | +--------+ | | C NoC |
|
|
| | V V | |
|
|
+------------------+ +------------------------+ | | +-----+
|
|
| |-->| |-->| |-->| CPU |
|
|
| |-->| |<--| | +-----+
|
|
| Mem NoC | | S NoC | +------------+
|
|
| |<--| |---------+ |
|
|
| |<--| |<------+ | | +--------+
|
|
+------------------+ +------------------------+ | | +-->| Slaves |
|
|
^ ^ ^ ^ ^ | | +--------+
|
|
| | | | | | V
|
|
+------+ | +-----+ +-----+ +---------+ +----------------+ +--------+
|
|
| CPUs | | | GPU | | DSP | | Masters |-->| P NoC |-->| Slaves |
|
|
+------+ | +-----+ +-----+ +---------+ +----------------+ +--------+
|
|
|
|
|
+-------+
|
|
| Modem |
|
|
+-------+
|
|
|
|
Terminology
|
|
-----------
|
|
|
|
Interconnect provider is the software definition of the interconnect hardware.
|
|
The interconnect providers on the above diagram are M NoC, S NoC, C NoC, P NoC
|
|
and Mem NoC.
|
|
|
|
Interconnect node is the software definition of the interconnect hardware
|
|
port. Each interconnect provider consists of multiple interconnect nodes,
|
|
which are connected to other SoC components including other interconnect
|
|
providers. The point on the diagram where the CPUs connect to the memory is
|
|
called an interconnect node, which belongs to the Mem NoC interconnect provider.
|
|
|
|
Interconnect endpoints are the first or the last element of the path. Every
|
|
endpoint is a node, but not every node is an endpoint.
|
|
|
|
Interconnect path is everything between two endpoints including all the nodes
|
|
that have to be traversed to reach from a source to destination node. It may
|
|
include multiple master-slave pairs across several interconnect providers.
|
|
|
|
Interconnect consumers are the entities which make use of the data paths exposed
|
|
by the providers. The consumers send requests to providers requesting various
|
|
throughput, latency and priority. Usually the consumers are device drivers, that
|
|
send request based on their needs. An example for a consumer is a video decoder
|
|
that supports various formats and image sizes.
|
|
|
|
Interconnect providers
|
|
----------------------
|
|
|
|
Interconnect provider is an entity that implements methods to initialize and
|
|
configure interconnect bus hardware. The interconnect provider drivers should
|
|
be registered with the interconnect provider core.
|
|
|
|
.. kernel-doc:: include/linux/interconnect-provider.h
|
|
|
|
Interconnect consumers
|
|
----------------------
|
|
|
|
Interconnect consumers are the clients which use the interconnect APIs to
|
|
get paths between endpoints and set their bandwidth/latency/QoS requirements
|
|
for these interconnect paths. These interfaces are not currently
|
|
documented.
|
|
|
|
Interconnect debugfs interfaces
|
|
-------------------------------
|
|
|
|
Like several other subsystems interconnect will create some files for debugging
|
|
and introspection. Files in debugfs are not considered ABI so application
|
|
software shouldn't rely on format details change between kernel versions.
|
|
|
|
``/sys/kernel/debug/interconnect/interconnect_summary``:
|
|
|
|
Show all interconnect nodes in the system with their aggregated bandwidth
|
|
request. Indented under each node show bandwidth requests from each device.
|
|
|
|
``/sys/kernel/debug/interconnect/interconnect_graph``:
|
|
|
|
Show the interconnect graph in the graphviz dot format. It shows all
|
|
interconnect nodes and links in the system and groups together nodes from the
|
|
same provider as subgraphs. The format is human-readable and can also be piped
|
|
through dot to generate diagrams in many graphical formats::
|
|
|
|
$ cat /sys/kernel/debug/interconnect/interconnect_graph | \
|
|
dot -Tsvg > interconnect_graph.svg
|