Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. 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