interconnect: Add debugfs test client

It's often useful during test, debug, and development to issue path
votes from shell. Add a debugfs client for this purpose.

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

Allowing userspace to directly enable and set bus rates can be dangerous
So, following in the footsteps of the regmap [0] and clk [1] frameworks,
keep these userspace controls compile-time disabled without Kconfig
options to enable them. Enabling this will require code changes to
define INTERCONNECT_ALLOW_WRITE_DEBUGFS.

[0] commit 09c6ecd394 ("regmap: Add support for writing to regmap registers via debugfs")
[1] commit 37215da555 ("clk: Add support for setting clk_rate via debugfs")

Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
Link: https://lore.kernel.org/r/20230807142914.12480-4-quic_mdtipton@quicinc.com
Signed-off-by: Georgi Djakov <djakov@kernel.org>

Documentation/driver-api/interconnect.rst

@@ -113,3 +113,28 @@ 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

drivers/interconnect/Makefile

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 CFLAGS_core.o				:= -I$(src)
-icc-core-objs				:= core.o bulk.o
+icc-core-objs				:= core.o bulk.o debugfs-client.o
 
 obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
 obj-$(CONFIG_INTERCONNECT_IMX)		+= imx/

drivers/interconnect/core.c

@@ -1116,6 +1116,9 @@ static int __init icc_init(void)
 			    icc_debugfs_dir, NULL, &icc_summary_fops);
 	debugfs_create_file("interconnect_graph", 0444,
 			    icc_debugfs_dir, NULL, &icc_graph_fops);
+
+	icc_debugfs_client_init(icc_debugfs_dir);
+
 	return 0;
 }
 

drivers/interconnect/debugfs-client.c

@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+#include <linux/debugfs.h>
+#include <linux/interconnect.h>
+#include <linux/platform_device.h>
+
+#include "internal.h"
+
+/*
+ * This can be dangerous, therefore don't provide any real compile time
+ * configuration option for this feature.
+ * People who want to use this will need to modify the source code directly.
+ */
+#undef INTERCONNECT_ALLOW_WRITE_DEBUGFS
+
+#if defined(INTERCONNECT_ALLOW_WRITE_DEBUGFS) && defined(CONFIG_DEBUG_FS)
+
+static LIST_HEAD(debugfs_paths);
+static DEFINE_MUTEX(debugfs_lock);
+
+static struct platform_device *pdev;
+static struct icc_path *cur_path;
+
+static char *src_node;
+static char *dst_node;
+static u32 avg_bw;
+static u32 peak_bw;
+static u32 tag;
+
+struct debugfs_path {
+	const char *src;
+	const char *dst;
+	struct icc_path *path;
+	struct list_head list;
+};
+
+static struct icc_path *get_path(const char *src, const char *dst)
+{
+	struct debugfs_path *path;
+
+	list_for_each_entry(path, &debugfs_paths, list) {
+		if (!strcmp(path->src, src) && !strcmp(path->dst, dst))
+			return path->path;
+	}
+
+	return NULL;
+}
+
+static int icc_get_set(void *data, u64 val)
+{
+	struct debugfs_path *debugfs_path;
+	char *src, *dst;
+	int ret = 0;
+
+	mutex_lock(&debugfs_lock);
+
+	rcu_read_lock();
+	src = rcu_dereference(src_node);
+	dst = rcu_dereference(dst_node);
+
+	/*
+	 * If we've already looked up a path, then use the existing one instead
+	 * of calling icc_get() again. This allows for updating previous BW
+	 * votes when "get" is written to multiple times for multiple paths.
+	 */
+	cur_path = get_path(src, dst);
+	if (cur_path) {
+		rcu_read_unlock();
+		goto out;
+	}
+
+	src = kstrdup(src, GFP_ATOMIC);
+	dst = kstrdup(dst, GFP_ATOMIC);
+	rcu_read_unlock();
+
+	if (!src || !dst) {
+		ret = -ENOMEM;
+		goto err_free;
+	}
+
+	cur_path = icc_get(&pdev->dev, src, dst);
+	if (IS_ERR(cur_path)) {
+		ret = PTR_ERR(cur_path);
+		goto err_free;
+	}
+
+	debugfs_path = kzalloc(sizeof(*debugfs_path), GFP_KERNEL);
+	if (!debugfs_path) {
+		ret = -ENOMEM;
+		goto err_put;
+	}
+
+	debugfs_path->path = cur_path;
+	debugfs_path->src = src;
+	debugfs_path->dst = dst;
+	list_add_tail(&debugfs_path->list, &debugfs_paths);
+
+	goto out;
+
+err_put:
+	icc_put(cur_path);
+err_free:
+	kfree(src);
+	kfree(dst);
+out:
+	mutex_unlock(&debugfs_lock);
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(icc_get_fops, NULL, icc_get_set, "%llu\n");
+
+static int icc_commit_set(void *data, u64 val)
+{
+	int ret;
+
+	mutex_lock(&debugfs_lock);
+
+	if (IS_ERR_OR_NULL(cur_path)) {
+		ret = PTR_ERR(cur_path);
+		goto out;
+	}
+
+	icc_set_tag(cur_path, tag);
+	ret = icc_set_bw(cur_path, avg_bw, peak_bw);
+out:
+	mutex_unlock(&debugfs_lock);
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(icc_commit_fops, NULL, icc_commit_set, "%llu\n");
+
+int icc_debugfs_client_init(struct dentry *icc_dir)
+{
+	struct dentry *client_dir;
+	int ret;
+
+	pdev = platform_device_alloc("icc-debugfs-client", PLATFORM_DEVID_NONE);
+
+	ret = platform_device_add(pdev);
+	if (ret) {
+		pr_err("%s: failed to add platform device: %d\n", __func__, ret);
+		platform_device_put(pdev);
+		return ret;
+	}
+
+	client_dir = debugfs_create_dir("test_client", icc_dir);
+
+	debugfs_create_str("src_node", 0600, client_dir, &src_node);
+	debugfs_create_str("dst_node", 0600, client_dir, &dst_node);
+	debugfs_create_file("get", 0200, client_dir, NULL, &icc_get_fops);
+	debugfs_create_u32("avg_bw", 0600, client_dir, &avg_bw);
+	debugfs_create_u32("peak_bw", 0600, client_dir, &peak_bw);
+	debugfs_create_u32("tag", 0600, client_dir, &tag);
+	debugfs_create_file("commit", 0200, client_dir, NULL, &icc_commit_fops);
+
+	return 0;
+}
+
+#else
+
+int icc_debugfs_client_init(struct dentry *icc_dir)
+{
+	return 0;
+}
+
+#endif

drivers/interconnect/internal.h

@@ -42,5 +42,6 @@ struct icc_path {
 };
 
 struct icc_path *icc_get(struct device *dev, const char *src, const char *dst);
+int icc_debugfs_client_init(struct dentry *icc_dir);
 
 #endif