.. SPDX-License-Identifier: GPL-2.0 =====================================Generic System Interconnect Subsystem===================================== Introduction------------ This framework is designed to provide a standard kernel interface to controlthe settings of the interconnects on an SoC. These settings can be throughput,latency and priority between multiple interconnected devices or functionalblocks. This can be controlled dynamically in order to save power or providemaximum performance. The interconnect bus is hardware with configurable parameters, which can beset on a data path according to the requests received from various drivers.An example of interconnect buses are the interconnects between variouscomponents or functional blocks in chipsets. There can be multiple interconnectson 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 NoCand Mem NoC. Interconnect node is the software definition of the interconnect hardwareport. Each interconnect provider consists of multiple interconnect nodes,which are connected to other SoC components including other interconnectproviders. The point on the diagram where the CPUs connect to the memory iscalled an interconnect node, which belongs to the Mem NoC interconnect provider. Interconnect endpoints are the first or the last element of the path. Everyendpoint is a node, but not every node is an endpoint. Interconnect path is everything between two endpoints including all the nodesthat have to be traversed to reach from a source to destination node. It mayinclude multiple master-slave pairs across several interconnect providers. Interconnect consumers are the entities which make use of the data paths exposedby the providers. The consumers send requests to providers requesting variousthroughput, latency and priority. Usually the consumers are device drivers, thatsend request based on their needs. An example for a consumer is a video decoderthat supports various formats and image sizes. Interconnect providers---------------------- Interconnect provider is an entity that implements methods to initialize andconfigure interconnect bus hardware. The interconnect provider drivers shouldbe 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 toget paths between endpoints and set their bandwidth/latency/QoS requirementsfor these interconnect paths.  These interfaces are not currentlydocumented. Interconnect debugfs interfaces------------------------------- Like several other subsystems interconnect will create some files for debuggingand introspection. Files in debugfs are not considered ABI so applicationsoftware 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 bandwidthrequest. 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 allinterconnect nodes and links in the system and groups together nodes from thesame provider as subgraphs. The format is human-readable and can also be pipedthrough dot to generate diagrams in many graphical formats::         $ cat /sys/kernel/debug/interconnect/interconnect_graph | \                dot -Tsvg > interconnect_graph.svg