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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/driver-api/interconnect.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-rw-r--r-- | Documentation/driver-api/interconnect.rst | 115 |
1 files changed, 115 insertions, 0 deletions
diff --git a/Documentation/driver-api/interconnect.rst b/Documentation/driver-api/interconnect.rst new file mode 100644 index 000000000..5ed4f57a6 --- /dev/null +++ b/Documentation/driver-api/interconnect.rst @@ -0,0 +1,115 @@ +.. 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 |