Subject: [PATCH v4 1/7] interconnect: Add generic on-chip interconnect API

From: [email-masked] (Matthias Kaehlcke)
Date: Fri, 6 Apr 2018 10:38:46 -0700

On Fri, Mar 09, 2018 at 11:09:52PM +0200, Georgi Djakov wrote:
> This patch introduce a new API to get requirements and configure the
> interconnect buses across the entire chipset to fit with the current
> demand.
> 
> The API is using a consumer/provider-based model, where the providers are
> the interconnect buses and the consumers could be various drivers.
> The consumers request interconnect resources (path) between endpoints and
> set the desired constraints on this data flow path. The providers receive
> requests from consumers and aggregate these requests for all master-slave
> pairs on that path. Then the providers configure each participating in the
> topology node according to the requested data flow path, physical links and
> constraints. The topology could be complicated and multi-tiered and is SoC
> specific.
> 
> Signed-off-by: Georgi Djakov <[email-masked]>
> ---
>  Documentation/interconnect/interconnect.rst |  96 ++++++
>  drivers/Kconfig                             |   2 +
>  drivers/Makefile                            |   1 +
>  drivers/interconnect/Kconfig                |  10 +
>  drivers/interconnect/Makefile               |   1 +
>  drivers/interconnect/core.c                 | 489 ++++++++++++++++++++++++++++
>  include/linux/interconnect-provider.h       | 109 +++++++
>  include/linux/interconnect.h                |  40 +++
>  8 files changed, 748 insertions(+)
>  create mode 100644 Documentation/interconnect/interconnect.rst
>  create mode 100644 drivers/interconnect/Kconfig
>  create mode 100644 drivers/interconnect/Makefile
>  create mode 100644 drivers/interconnect/core.c
>  create mode 100644 include/linux/interconnect-provider.h
>  create mode 100644 include/linux/interconnect.h
> 
> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst
> new file mode 100644
> index 000000000000..23eba68e8424
> --- /dev/null
> +++ b/Documentation/interconnect/interconnect.rst
> @@ -0,0 +1,96 @@
> +.. 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 a 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 a 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 a 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 and Mem
> +NoC.

Should P NoC be part of that list?

> +
> +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 connects 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 a interconnect bus hardware. The interconnect provider drivers should
> +be registered with the interconnect provider core.
> +
> +The interconnect framework provider API functions are documented in
> +.. 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.
> +
> +The interconnect framework consumer API functions are documented in
> +.. kernel-doc:: include/linux/interconnect.h
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 879dc0604cba..96a1db022cee 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -219,4 +219,6 @@ source "drivers/siox/Kconfig"
>  
>  source "drivers/slimbus/Kconfig"
>  
> +source "drivers/interconnect/Kconfig"
> +
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 24cd47014657..0cca95740d9b 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)		+= tee/
>  obj-$(CONFIG_MULTIPLEXER)	+= mux/
>  obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
>  obj-$(CONFIG_SIOX)		+= siox/
> +obj-$(CONFIG_INTERCONNECT)	+= interconnect/
> diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
> new file mode 100644
> index 000000000000..a261c7d41deb
> --- /dev/null
> +++ b/drivers/interconnect/Kconfig
> @@ -0,0 +1,10 @@
> +menuconfig INTERCONNECT
> +	tristate "On-Chip Interconnect management support"
> +	help
> +	  Support for management of the on-chip interconnects.
> +
> +	  This framework is designed to provide a generic interface for
> +	  managing the interconnects in a SoC.
> +
> +	  If unsure, say no.
> +
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> new file mode 100644
> index 000000000000..5edf0ae80818
> --- /dev/null
> +++ b/drivers/interconnect/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_INTERCONNECT)		+= core.o
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> new file mode 100644
> index 000000000000..6306e258b9b9
> --- /dev/null
> +++ b/drivers/interconnect/core.c
> @@ -0,0 +1,489 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Interconnect framework core driver
> + *
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[email-masked]>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/interconnect.h>
> +#include <linux/interconnect-provider.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +static DEFINE_IDR(icc_idr);
> +static LIST_HEAD(icc_provider_list);
> +static DEFINE_MUTEX(icc_provider_list_mutex);
> +static DEFINE_MUTEX(icc_path_mutex);
> +
> +/**
> + * struct icc_req - constraints that are attached to each node
> + *
> + * @req_node: entry in list of requests for the particular @node
> + * @node: the interconnect node to which this constraint applies
> + * @avg_bw: an integer describing the average bandwidth in kbps
> + * @peak_bw: an integer describing the peak bandwidth in kbps
> + */
> +struct icc_req {
> +	struct hlist_node req_node;
> +	struct icc_node *node;
> +	u32 avg_bw;
> +	u32 peak_bw;
> +};
> +
> +/**
> + * struct icc_path - interconnect path structure
> + * @num_nodes: number of hops (nodes)
> + * @reqs: array of the requests applicable to this path of nodes
> + */
> +struct icc_path {
> +	size_t num_nodes;
> +	struct icc_req reqs[0];
> +};
> +
> +static struct icc_node *node_find(const int id)
> +{
> +	struct icc_node *node;
> +
> +	node = idr_find(&icc_idr, id);
> +
> +	return node;
> +}
> +
> +static struct icc_path *path_allocate(struct icc_node *node, ssize_t num_nodes)
> +{
> +	struct icc_path *path;
> +	size_t i;
> +
> +	path = kzalloc(sizeof(*path) + num_nodes * sizeof(*path->reqs),
> +		       GFP_KERNEL);
> +	if (!path)
> +		return ERR_PTR(-ENOMEM);
> +
> +	path->num_nodes = num_nodes;
> +
> +	for (i = 0; i < num_nodes; i++) {
> +		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
> +
> +		path->reqs[i].node = node;
> +		/* reference to previous node was saved during path traversal */
> +		node = node->reverse;
> +	}
> +
> +	return path;
> +}
> +
> +static struct icc_path *path_find(struct icc_node *src, struct icc_node *dst)
> +{
> +	struct icc_node *node = NULL;
> +	struct list_head traverse_list;
> +	struct list_head edge_list;
> +	struct list_head tmp_list;
> +	size_t i, number = 0;
> +	bool found = false;
> +
> +	INIT_LIST_HEAD(&traverse_list);
> +	INIT_LIST_HEAD(&edge_list);
> +	INIT_LIST_HEAD(&tmp_list);
> +
> +	list_add_tail(&src->search_list, &traverse_list);
> +
> +	do {
> +		list_for_each_entry(node, &traverse_list, search_list) {
> +			if (node == dst) {
> +				found = true;
> +				list_add(&node->search_list, &tmp_list);
> +				break;
> +			}
> +			for (i = 0; i < node->num_links; i++) {
> +				struct icc_node *tmp = node->links[i];
> +
> +				if (!tmp)
> +					return ERR_PTR(-ENOENT);
> +
> +				if (tmp->is_traversed)
> +					continue;
> +
> +				tmp->is_traversed = true;
> +				tmp->reverse = node;
> +				list_add_tail(&tmp->search_list, &edge_list);
> +			}
> +		}
> +		if (found)
> +			break;
> +
> +		list_splice_init(&traverse_list, &tmp_list);
> +		list_splice_init(&edge_list, &traverse_list);
> +
> +		/* count the number of nodes */
> +		number++;
> +
> +	} while (!list_empty(&traverse_list));
> +
> +	/* reset the traversed state */
> +	list_for_each_entry(node, &tmp_list, search_list)
> +		node->is_traversed = false;
> +
> +	if (found)
> +		return path_allocate(dst, number);
> +
> +	return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +static int path_init(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users++;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +static void node_aggregate(struct icc_node *node)
> +{
> +	struct icc_req *r;
> +	u32 agg_avg = 0;

Should this be u64 to avoid overflow in case of a large number of
constraints and high bandwidths?

> +	u32 agg_peak = 0;
> +
> +	hlist_for_each_entry(r, &node->req_list, req_node) {
> +		/* sum(averages) and max(peaks) */
> +		agg_avg += r->avg_bw;
> +		agg_peak = max(agg_peak, r->peak_bw);
> +	}
> +
> +	node->avg_bw = agg_avg;

Is it really intended to store the sum of averages here rather than
the overall average?

> +	node->peak_bw = agg_peak;
> +}
> +
> +static void provider_aggregate(struct icc_provider *provider, u32 *avg_bw,
> +			       u32 *peak_bw)
> +{
> +	struct icc_node *n;
> +	u32 agg_avg = 0;

See above.

> +	u32 agg_peak = 0;
> +
> +	/* aggregate for the interconnect provider */
> +	list_for_each_entry(n, &provider->nodes, node_list) {
> +		/* sum the average and max the peak */
> +		agg_avg += n->avg_bw;
> +		agg_peak = max(agg_peak, n->peak_bw);
> +	}
> +
> +	*avg_bw = agg_avg;

See above.

> +	*peak_bw = agg_peak;
> +}
> +
> +static int constraints_apply(struct icc_path *path)
> +{
> +	struct icc_node *next, *prev = NULL;
> +	int i;
> +
> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
> +		struct icc_provider *provider;
> +		u32 avg_bw = 0;
> +		u32 peak_bw = 0;
> +		int ret;
> +
> +		next = path->reqs[i].node;
> +		/*
> +		 * Both endpoints should be valid master-slave pairs of the
> +		 * same interconnect provider that will be configured.
> +		 */
> +		if (!next || !prev)
> +			continue;
> +
> +		if (next->provider != prev->provider)
> +			continue;
> +
> +		provider = next->provider;
> +		mutex_lock(&provider->lock);
> +
> +		/* aggregate requests for the provider */
> +		provider_aggregate(provider, &avg_bw, &peak_bw);
> +
> +		if (provider->set) {
> +			/* set the constraints */
> +			ret = provider->set(prev, next, avg_bw, peak_bw);
> +		}
> +
> +		mutex_unlock(&provider->lock);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_set() - set constraints on an interconnect path between two endpoints
> + * @path: reference to the path returned by icc_get()
> + * @avg_bw: average bandwidth in kbps
> + * @peak_bw: peak bandwidth in kbps
> + *
> + * This function is used by an interconnect consumer to express its own needs
> + * in term of bandwidth and QoS for a previously requested path between two
> + * endpoints. The requests are aggregated and each node is updated accordingly.
> + *
> + * Returns 0 on success, or an approproate error code otherwise.
> + */
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path)
> +		return 0;
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +
> +		mutex_lock(&icc_path_mutex);
> +
> +		/* update the consumer request for this path */
> +		path->reqs[i].avg_bw = avg_bw;
> +		path->reqs[i].peak_bw = peak_bw;
> +
> +		/* aggregate requests for this node */
> +		node_aggregate(node);
> +
> +		mutex_unlock(&icc_path_mutex);
> +	}
> +
> +	ret = constraints_apply(path);
> +	if (ret)
> +		pr_err("interconnect: error applying constraints (%d)", ret);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(icc_set);
> +
> +/**
> + * icc_get() - return a handle for path between two endpoints
> + * @src_id: source device port id
> + * @dst_id: destination device port id
> + *
> + * This function will search for a path between two endpoints and return an
> + * icc_path handle on success. Use icc_put() to release
> + * constraints when the they are not needed anymore.
> + *
> + * Return: icc_path pointer on success, or ERR_PTR() on error
> + */
> +struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	struct icc_node *src, *dst;
> +	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
> +
> +	src = node_find(src_id);
> +	if (!src)
> +		goto out;
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		goto out;
> +
> +	mutex_lock(&icc_path_mutex);
> +	path = path_find(src, dst);
> +	mutex_unlock(&icc_path_mutex);
> +	if (IS_ERR(path))
> +		goto out;
> +
> +	path_init(path);
> +
> +out:
> +	return path;
> +}
> +EXPORT_SYMBOL_GPL(icc_get);
> +
> +/**
> + * icc_put() - release the reference to the icc_path
> + * @path: interconnect path
> + *
> + * Use this function to release the constraints on a path when the path is
> + * no longer needed. The constraints will be re-aggregated.
> + */
> +void icc_put(struct icc_path *path)
> +{
> +	struct icc_node *node;
> +	size_t i;
> +	int ret;
> +
> +	if (!path || WARN_ON_ONCE(IS_ERR(path)))
> +		return;
> +
> +	ret = icc_set(path, 0, 0);
> +	if (ret)
> +		pr_err("%s: error (%d)\n", __func__, ret);
> +
> +	for (i = 0; i < path->num_nodes; i++) {
> +		node = path->reqs[i].node;
> +		hlist_del(&path->reqs[i].req_node);
> +
> +		mutex_lock(&node->provider->lock);
> +		node->provider->users--;
> +		mutex_unlock(&node->provider->lock);
> +	}
> +
> +	kfree(path);
> +}
> +EXPORT_SYMBOL_GPL(icc_put);
> +
> +/**
> + * icc_node_create() - create a node
> + * @id: node id
> + *
> + * Return: icc_node pointer on success, or ERR_PTR() on error
> + */
> +struct icc_node *icc_node_create(int id)
> +{
> +	struct icc_node *node;
> +
> +	/* check if node already exists */
> +	node = node_find(id);
> +	if (node)
> +		return node;
> +
> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
> +	if (!node)
> +		return ERR_PTR(-ENOMEM);
> +
> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
> +	if (WARN(id < 0, "couldn't get idr"))
> +		return ERR_PTR(id);
> +
> +	node->id = id;
> +
> +	return node;
> +}
> +EXPORT_SYMBOL_GPL(icc_node_create);
> +
> +/**
> + * icc_link_create() - create a link between two nodes
> + * @src_id: source node id
> + * @dst_id: destination node id
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	struct icc_node *dst;
> +	struct icc_node **new;
> +	int ret = 0;
> +
> +	if (IS_ERR_OR_NULL(node))
> +		return PTR_ERR(node);
> +
> +	mutex_lock(&node->provider->lock);
> +
> +	dst = node_find(dst_id);
> +	if (!dst)
> +		dst = icc_node_create(dst_id);
> +
> +	new = krealloc(node->links,
> +		       (node->num_links + 1) * sizeof(*node->links),
> +		       GFP_KERNEL);
> +	if (!new) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	node->links = new;
> +	node->links[node->num_links++] = dst;
> +
> +out:
> +	mutex_unlock(&node->provider->lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_link_create);
> +
> +/**
> + * icc_add_node() - add an interconnect node to interconnect provider
> + * @node: pointer to the interconnect node
> + * @provider: pointer to the interconnect provider
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	if (WARN_ON(!node))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	node->provider = provider;
> +
> +	mutex_lock(&provider->lock);
> +	list_add_tail(&node->node_list, &provider->nodes);
> +	mutex_unlock(&provider->lock);
> +
> +	return 0;
> +}
> +
> +/**
> + * icc_add_provider() - add a new interconnect provider
> + * @icc_provider: the interconnect provider that will be added into topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_add_provider(struct icc_provider *provider)
> +{
> +	if (WARN_ON(!provider))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!provider->set))
> +		return -EINVAL;
> +
> +	mutex_init(&provider->lock);
> +	INIT_LIST_HEAD(&provider->nodes);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_add(&provider->provider_list, &icc_provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	dev_dbg(provider->dev, "interconnect provider added to topology\n");
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_add_provider);
> +
> +/**
> + * icc_del_provider() - delete previously added interconnect provider
> + * @icc_provider: the interconnect provider that will be removed from topology
> + *
> + * Return: 0 on success, or an error code otherwise
> + */
> +int icc_del_provider(struct icc_provider *provider)
> +{
> +	mutex_lock(&provider->lock);
> +	if (provider->users) {
> +		pr_warn("interconnect provider still has %d users\n",
> +			provider->users);
> +	}
> +	mutex_unlock(&provider->lock);
> +
> +	mutex_lock(&icc_provider_list_mutex);
> +	list_del(&provider->provider_list);
> +	mutex_unlock(&icc_provider_list_mutex);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(icc_del_provider);
> +
> +MODULE_AUTHOR("Georgi Djakov <[email-masked]");
> +MODULE_DESCRIPTION("Interconnect Driver Core");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/interconnect-provider.h b/include/linux/interconnect-provider.h
> new file mode 100644
> index 000000000000..779b5b5b1306
> --- /dev/null
> +++ b/include/linux/interconnect-provider.h
> @@ -0,0 +1,109 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[email-masked]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_PROVIDER_H
> +#define _LINUX_INTERCONNECT_PROVIDER_H
> +
> +#include <linux/interconnect.h>
> +
> +struct icc_node;
> +
> +/**
> + * struct icc_provider - interconnect provider (controller) entity that might
> + * provide multiple interconnect controls
> + *
> + * @provider_list: list of the registered interconnect providers
> + * @nodes: internal list of the interconnect provider nodes
> + * @set: pointer to device specific set operation function
> + * @dev: the device this interconnect provider belongs to
> + * @lock: lock to provide consistency during aggregation/update of constraints
> + * @users: count of active users
> + * @data: pointer to private data
> + */
> +struct icc_provider {
> +	struct list_head	provider_list;
> +	struct list_head	nodes;
> +	int (*set)(struct icc_node *src, struct icc_node *dst,
> +		   u32 avg_bw, u32 peak_bw);
> +	struct device		*dev;
> +	struct mutex		lock;
> +	int			users;
> +	void			*data;
> +};
> +
> +/**
> + * struct icc_node - entity that is part of the interconnect topology
> + *
> + * @id: platform specific node id
> + * @name: node name used in debugfs
> + * @links: a list of targets where we can go next when traversing
> + * @num_links: number of links to other interconnect nodes
> + * @provider: points to the interconnect provider of this node
> + * @node_list: list of interconnect nodes associated with @provider
> + * @search_list: list used when walking the nodes graph
> + * @reverse: pointer to previous node when walking the nodes graph
> + * @is_traversed: flag that is used when walking the nodes graph
> + * @req_list: a list of QoS constraint requests associated with this node
> + * @avg_bw: aggregated value of average bandwidth
> + * @peak_bw: aggregated value of peak bandwidth
> + * @data: pointer to private data
> + */
> +struct icc_node {
> +	int			id;
> +	const char              *name;
> +	struct icc_node		**links;
> +	size_t			num_links;
> +
> +	struct icc_provider	*provider;
> +	struct list_head	node_list;
> +	struct list_head	orphan_list;

orphan_list is not used (nor documented)

> +	struct list_head	search_list;
> +	struct icc_node		*reverse;
> +	bool			is_traversed;
> +	struct hlist_head	req_list;
> +	u32			avg_bw;
> +	u32			peak_bw;
> +	void			*data;
> +};
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_node *icc_node_create(int id);
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider);
> +int icc_link_create(struct icc_node *node, const int dst_id);
> +int icc_add_provider(struct icc_provider *provider);
> +int icc_del_provider(struct icc_provider *provider);
> +
> +#else
> +
> +static inline struct icc_node *icc_node_create(int id)
> +{
> +	return ERR_PTR(-ENOTSUPP);
> +}
> +
> +int icc_node_add(struct icc_node *node, struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_link_create(struct icc_node *node, const int dst_id)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_add_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline int icc_del_provider(struct icc_provider *provider)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_PROVIDER_H */
> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> new file mode 100644
> index 000000000000..5a7cf72b76a5
> --- /dev/null
> +++ b/include/linux/interconnect.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2018, Linaro Ltd.
> + * Author: Georgi Djakov <[email-masked]>
> + */
> +
> +#ifndef _LINUX_INTERCONNECT_H
> +#define _LINUX_INTERCONNECT_H
> +
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +
> +struct icc_path;
> +struct device;
> +
> +#if IS_ENABLED(CONFIG_INTERCONNECT)
> +
> +struct icc_path *icc_get(const int src_id, const int dst_id);
> +void icc_put(struct icc_path *path);
> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
> +
> +#else
> +
> +static inline struct icc_path *icc_get(const int src_id, const int dst_id)
> +{
> +	return NULL;
> +}
> +
> +static inline void icc_put(struct icc_path *path)
> +{
> +}
> +
> +static inline int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
> +{
> +	return 0;
> +}
> +
> +#endif /* CONFIG_INTERCONNECT */
> +
> +#endif /* _LINUX_INTERCONNECT_H */