interconnect: Add generic on-chip interconnect API

This patch introduces 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 node along the path
to support a bandwidth that satisfies all bandwidth requests that cross
through that node. The topology could be complicated and multi-tiered and
is SoC specific.

Reviewed-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

5 files changed, 585 insertions, 0 deletions

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 4f9f99057ff8..45f9decb9848 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -228,4 +228,6 @@ source "drivers/siox/Kconfig"
 
 source "drivers/slimbus/Kconfig"
 
+source "drivers/interconnect/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index e1ce029d28fd..bb15b9d0e793 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -186,3 +186,4 @@ obj-$(CONFIG_MULTIPLEXER)	+= mux/
 obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
 obj-$(CONFIG_SIOX)		+= siox/
 obj-$(CONFIG_GNSS)		+= gnss/
+obj-$(CONFIG_INTERCONNECT)	+= interconnect/
diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig
new file mode 100644
index 000000000000..a261c7d41deb
--- /dev/null
+++ b/drivers/interconnect/Kconfig
@@ -0,0 +1,10 @@
+menuconfig INTERCONNECT
+	tristate "On-Chip Interconnect management support"
+	help
+	  Support for management of the on-chip interconnects.
+
+	  This framework is designed to provide a generic interface for
+	  managing the interconnects in a SoC.
+
+	  If unsure, say no.
+
diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
new file mode 100644
index 000000000000..7a01f33b5593
--- /dev/null
+++ b/drivers/interconnect/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+icc-core-objs				:= core.o
+
+obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
new file mode 100644
index 000000000000..2b937b4f43c4
--- /dev/null
+++ b/drivers/interconnect/core.c
@@ -0,0 +1,567 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Interconnect framework core driver
+ *
+ * Copyright (c) 2017-2019, Linaro Ltd.
+ * Author: Georgi Djakov <georgi.djakov@linaro.org>
+ */
+
+#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>
+#include <linux/overflow.h>
+
+static DEFINE_IDR(icc_idr);
+static LIST_HEAD(icc_providers);
+static DEFINE_MUTEX(icc_lock);
+
+/**
+ * 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
+ * @dev: reference to the device that sets the constraints
+ * @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;
+	struct device *dev;
+	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[];
+};
+
+static struct icc_node *node_find(const int id)
+{
+	return idr_find(&icc_idr, id);
+}
+
+static struct icc_path *path_init(struct device *dev, struct icc_node *dst,
+				  ssize_t num_nodes)
+{
+	struct icc_node *node = dst;
+	struct icc_path *path;
+	int i;
+
+	path = kzalloc(struct_size(path, reqs, num_nodes), GFP_KERNEL);
+	if (!path)
+		return ERR_PTR(-ENOMEM);
+
+	path->num_nodes = num_nodes;
+
+	for (i = num_nodes - 1; i >= 0; i--) {
+		node->provider->users++;
+		hlist_add_head(&path->reqs[i].req_node, &node->req_list);
+		path->reqs[i].node = node;
+		path->reqs[i].dev = dev;
+		/* reference to previous node was saved during path traversal */
+		node = node->reverse;
+	}
+
+	return path;
+}
+
+static struct icc_path *path_find(struct device *dev, struct icc_node *src,
+				  struct icc_node *dst)
+{
+	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
+	struct icc_node *n, *node = NULL;
+	struct list_head traverse_list;
+	struct list_head edge_list;
+	struct list_head visited_list;
+	size_t i, depth = 1;
+	bool found = false;
+
+	INIT_LIST_HEAD(&traverse_list);
+	INIT_LIST_HEAD(&edge_list);
+	INIT_LIST_HEAD(&visited_list);
+
+	list_add(&src->search_list, &traverse_list);
+	src->reverse = NULL;
+
+	do {
+		list_for_each_entry_safe(node, n, &traverse_list, search_list) {
+			if (node == dst) {
+				found = true;
+				list_splice_init(&edge_list, &visited_list);
+				list_splice_init(&traverse_list, &visited_list);
+				break;
+			}
+			for (i = 0; i < node->num_links; i++) {
+				struct icc_node *tmp = node->links[i];
+
+				if (!tmp) {
+					path = ERR_PTR(-ENOENT);
+					goto out;
+				}
+
+				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, &visited_list);
+		list_splice_init(&edge_list, &traverse_list);
+
+		/* count the hops including the source */
+		depth++;
+
+	} while (!list_empty(&traverse_list));
+
+out:
+
+	/* reset the traversed state */
+	list_for_each_entry_reverse(n, &visited_list, search_list)
+		n->is_traversed = false;
+
+	if (found)
+		path = path_init(dev, dst, depth);
+
+	return path;
+}
+
+/*
+ * We want the path to honor all bandwidth requests, so the average and peak
+ * bandwidth requirements from each consumer are aggregated at each node.
+ * The aggregation is platform specific, so each platform can customize it by
+ * implementing its own aggregate() function.
+ */
+
+static int aggregate_requests(struct icc_node *node)
+{
+	struct icc_provider *p = node->provider;
+	struct icc_req *r;
+
+	node->avg_bw = 0;
+	node->peak_bw = 0;
+
+	hlist_for_each_entry(r, &node->req_list, req_node)
+		p->aggregate(node, r->avg_bw, r->peak_bw,
+			     &node->avg_bw, &node->peak_bw);
+
+	return 0;
+}
+
+static int apply_constraints(struct icc_path *path)
+{
+	struct icc_node *next, *prev = NULL;
+	int ret = -EINVAL;
+	int i;
+
+	for (i = 0; i < path->num_nodes; i++) {
+		next = path->reqs[i].node;
+
+		/*
+		 * Both endpoints should be valid master-slave pairs of the
+		 * same interconnect provider that will be configured.
+		 */
+		if (!prev || next->provider != prev->provider) {
+			prev = next;
+			continue;
+		}
+
+		/* set the constraints */
+		ret = next->provider->set(prev, next);
+		if (ret)
+			goto out;
+
+		prev = next;
+	}
+out:
+	return ret;
+}
+
+/**
+ * icc_set_bw() - set bandwidth constraints on an interconnect path
+ * @path: reference to the path returned by icc_get()
+ * @avg_bw: average bandwidth in kilobytes per second
+ * @peak_bw: peak bandwidth in kilobytes per second
+ *
+ * This function is used by an interconnect consumer to express its own needs
+ * in terms of bandwidth for a previously requested path between two endpoints.
+ * The requests are aggregated and each node is updated accordingly. The entire
+ * path is locked by a mutex to ensure that the set() is completed.
+ * The @path can be NULL when the "interconnects" DT properties is missing,
+ * which will mean that no constraints will be set.
+ *
+ * Returns 0 on success, or an appropriate error code otherwise.
+ */
+int icc_set_bw(struct icc_path *path, u32 avg_bw, u32 peak_bw)
+{
+	struct icc_node *node;
+	size_t i;
+	int ret;
+
+	if (!path)
+		return 0;
+
+	mutex_lock(&icc_lock);
+
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+
+		/* 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 */
+		aggregate_requests(node);
+	}
+
+	ret = apply_constraints(path);
+	if (ret)
+		pr_debug("interconnect: error applying constraints (%d)\n",
+			 ret);
+
+	mutex_unlock(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_set_bw);
+
+/**
+ * icc_get() - return a handle for path between two endpoints
+ * @dev: the device requesting the path
+ * @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 they are not needed anymore.
+ * If the interconnect API is disabled, NULL is returned and the consumer
+ * drivers will still build. Drivers are free to handle this specifically,
+ * but they don't have to.
+ *
+ * Return: icc_path pointer on success, ERR_PTR() on error or NULL if the
+ * interconnect API is disabled.
+ */
+struct icc_path *icc_get(struct device *dev, const int src_id, const int dst_id)
+{
+	struct icc_node *src, *dst;
+	struct icc_path *path = ERR_PTR(-EPROBE_DEFER);
+
+	mutex_lock(&icc_lock);
+
+	src = node_find(src_id);
+	if (!src)
+		goto out;
+
+	dst = node_find(dst_id);
+	if (!dst)
+		goto out;
+
+	path = path_find(dev, src, dst);
+	if (IS_ERR(path))
+		dev_err(dev, "%s: invalid path=%ld\n", __func__, PTR_ERR(path));
+
+out:
+	mutex_unlock(&icc_lock);
+	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(IS_ERR(path)))
+		return;
+
+	ret = icc_set_bw(path, 0, 0);
+	if (ret)
+		pr_err("%s: error (%d)\n", __func__, ret);
+
+	mutex_lock(&icc_lock);
+	for (i = 0; i < path->num_nodes; i++) {
+		node = path->reqs[i].node;
+		hlist_del(&path->reqs[i].req_node);
+		if (!WARN_ON(!node->provider->users))
+			node->provider->users--;
+	}
+	mutex_unlock(&icc_lock);
+
+	kfree(path);
+}
+EXPORT_SYMBOL_GPL(icc_put);
+
+static struct icc_node *icc_node_create_nolock(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 (id < 0) {
+		WARN(1, "%s: couldn't get idr\n", __func__);
+		kfree(node);
+		return ERR_PTR(id);
+	}
+
+	node->id = id;
+
+	return node;
+}
+
+/**
+ * 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;
+
+	mutex_lock(&icc_lock);
+
+	node = icc_node_create_nolock(id);
+
+	mutex_unlock(&icc_lock);
+
+	return node;
+}
+EXPORT_SYMBOL_GPL(icc_node_create);
+
+/**
+ * icc_node_destroy() - destroy a node
+ * @id: node id
+ */
+void icc_node_destroy(int id)
+{
+	struct icc_node *node;
+
+	mutex_lock(&icc_lock);
+
+	node = node_find(id);
+	if (node) {
+		idr_remove(&icc_idr, node->id);
+		WARN_ON(!hlist_empty(&node->req_list));
+	}
+
+	mutex_unlock(&icc_lock);
+
+	kfree(node);
+}
+EXPORT_SYMBOL_GPL(icc_node_destroy);
+
+/**
+ * icc_link_create() - create a link between two nodes
+ * @node: source node id
+ * @dst_id: destination node id
+ *
+ * Create a link between two nodes. The nodes might belong to different
+ * interconnect providers and the @dst_id node might not exist (if the
+ * provider driver has not probed yet). So just create the @dst_id node
+ * and when the actual provider driver is probed, the rest of the node
+ * data is filled.
+ *
+ * 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 (!node->provider)
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	dst = node_find(dst_id);
+	if (!dst) {
+		dst = icc_node_create_nolock(dst_id);
+
+		if (IS_ERR(dst)) {
+			ret = PTR_ERR(dst);
+			goto out;
+		}
+	}
+
+	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(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_link_create);
+
+/**
+ * icc_link_destroy() - destroy a link between two nodes
+ * @src: pointer to source node
+ * @dst: pointer to destination node
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_link_destroy(struct icc_node *src, struct icc_node *dst)
+{
+	struct icc_node **new;
+	size_t slot;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(src))
+		return -EINVAL;
+
+	if (IS_ERR_OR_NULL(dst))
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	for (slot = 0; slot < src->num_links; slot++)
+		if (src->links[slot] == dst)
+			break;
+
+	if (WARN_ON(slot == src->num_links)) {
+		ret = -ENXIO;
+		goto out;
+	}
+
+	src->links[slot] = src->links[--src->num_links];
+
+	new = krealloc(src->links, src->num_links * sizeof(*src->links),
+		       GFP_KERNEL);
+	if (new)
+		src->links = new;
+
+out:
+	mutex_unlock(&icc_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(icc_link_destroy);
+
+/**
+ * icc_node_add() - add interconnect node to interconnect provider
+ * @node: pointer to the interconnect node
+ * @provider: pointer to the interconnect provider
+ */
+void icc_node_add(struct icc_node *node, struct icc_provider *provider)
+{
+	mutex_lock(&icc_lock);
+
+	node->provider = provider;
+	list_add_tail(&node->node_list, &provider->nodes);
+
+	mutex_unlock(&icc_lock);
+}
+EXPORT_SYMBOL_GPL(icc_node_add);
+
+/**
+ * icc_node_del() - delete interconnect node from interconnect provider
+ * @node: pointer to the interconnect node
+ */
+void icc_node_del(struct icc_node *node)
+{
+	mutex_lock(&icc_lock);
+
+	list_del(&node->node_list);
+
+	mutex_unlock(&icc_lock);
+}
+EXPORT_SYMBOL_GPL(icc_node_del);
+
+/**
+ * icc_provider_add() - add a new interconnect provider
+ * @provider: the interconnect provider that will be added into topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_provider_add(struct icc_provider *provider)
+{
+	if (WARN_ON(!provider->set))
+		return -EINVAL;
+
+	mutex_lock(&icc_lock);
+
+	INIT_LIST_HEAD(&provider->nodes);
+	list_add_tail(&provider->provider_list, &icc_providers);
+
+	mutex_unlock(&icc_lock);
+
+	dev_dbg(provider->dev, "interconnect provider added to topology\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_provider_add);
+
+/**
+ * icc_provider_del() - delete previously added interconnect provider
+ * @provider: the interconnect provider that will be removed from topology
+ *
+ * Return: 0 on success, or an error code otherwise
+ */
+int icc_provider_del(struct icc_provider *provider)
+{
+	mutex_lock(&icc_lock);
+	if (provider->users) {
+		pr_warn("interconnect provider still has %d users\n",
+			provider->users);
+		mutex_unlock(&icc_lock);
+		return -EBUSY;
+	}
+
+	if (!list_empty(&provider->nodes)) {
+		pr_warn("interconnect provider still has nodes\n");
+		mutex_unlock(&icc_lock);
+		return -EBUSY;
+	}
+
+	list_del(&provider->provider_list);
+	mutex_unlock(&icc_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(icc_provider_del);
+
+MODULE_AUTHOR("Georgi Djakov <georgi.djakov@linaro.org>");
+MODULE_DESCRIPTION("Interconnect Driver Core");
+MODULE_LICENSE("GPL v2");