From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops There's some internal state that ftrace_ops needs to have set, but since it can be declared outside of the ftrace.c code, it calls ftrace_ops_init() on the ops in every global function. The issue is that if two tasks call it on the same ops at the same time it is possible to have the initialization of one corrupt the initialization of the other call. Create a ops_mutex to use to synchronize every initialization of the ftrace_ops. The mutex is taken within checking the ftrace_ops flag that states it was initializied but the flag is checked again after the mutex has been taken. Checking first outside the mutex allows it to shortcut having to take the mutex. But then the check needs to be done again after the mute is taken in case of races. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock") Reported-by: sashiko-bot@kernel.org Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/ Signed-off-by: Steven Rostedt --- Documentation/driver-api/interconnect.rst | 152 ++++++++++++++++++++++++++++++ 1 file changed, 152 insertions(+) create mode 100644 Documentation/driver-api/interconnect.rst (limited to 'Documentation/driver-api/interconnect.rst') diff --git a/Documentation/driver-api/interconnect.rst b/Documentation/driver-api/interconnect.rst new file mode 100644 index 000000000..cebb77b49 --- /dev/null +++ b/Documentation/driver-api/interconnect.rst @@ -0,0 +1,152 @@ +.. 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 + +.. kernel-doc:: drivers/interconnect/core.c + :functions: icc_provider_init icc_provider_register icc_provider_deregister + icc_node_create icc_node_create_dyn icc_node_destroy + icc_node_add icc_node_del icc_nodes_remove icc_node_set_name + icc_link_create icc_link_nodes + +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. + +.. kernel-doc:: drivers/interconnect/core.c + :functions: devm_of_icc_get of_icc_get_by_index of_icc_get icc_get + icc_put icc_enable icc_disable icc_set_bw icc_set_tag + icc_get_name + +.. kernel-doc:: drivers/interconnect/bulk.c + +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 + +The ``test-client`` directory provides interfaces for issuing BW requests to +any arbitrary path. Note that for safety reasons, this feature is disabled by +default without a Kconfig to enable it. Enabling it requires code changes to +``#define INTERCONNECT_ALLOW_WRITE_DEBUGFS``. Example usage:: + + cd /sys/kernel/debug/interconnect/test-client/ + + # Configure node endpoints for the path from CPU to DDR on + # qcom/sm8550. + echo chm_apps > src_node + echo ebi > dst_node + + # Get path between src_node and dst_node. This is only + # necessary after updating the node endpoints. + echo 1 > get + + # Set desired BW to 1GBps avg and 2GBps peak. + echo 1000000 > avg_bw + echo 2000000 > peak_bw + + # Vote for avg_bw and peak_bw on the latest path from "get". + # Voting for multiple paths is possible by repeating this + # process for different nodes endpoints. + echo 1 > commit -- cgit v1.3.1