[2/2] powercap/drivers/dtpm: Allow dtpm node device creation through configfs

diff --git a/drivers/powercap/Kconfig b/drivers/powercap/Kconfig
index 8242e8c5ed77..599b41e4e0a7 100644
--- a/drivers/powercap/Kconfig
+++ b/drivers/powercap/Kconfig
@@ -50,6 +50,14 @@  config DTPM
 	  This enables support for the power capping for the dynamic
 	  thermal power management userspace engine.
 
+config DTPM_CONFIGFS
+	tristate "Dynamic Thermal Power Management configuration via configfs"
+	depends on DTPM && CONFIGFS_FS
+	help
+	  This enables support for creating the DTPM device hierarchy
+	  via configfs giving the userspace full control of the
+	  thermal constraint representation.
+
 config DTPM_CPU
 	bool "Add CPU power capping based on the energy model"
 	depends on DTPM && ENERGY_MODEL
diff --git a/drivers/powercap/Makefile b/drivers/powercap/Makefile
index fabcf388a8d3..519cabc624c3 100644
--- a/drivers/powercap/Makefile
+++ b/drivers/powercap/Makefile
@@ -1,5 +1,6 @@ 
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_DTPM) += dtpm.o
+obj-$(CONFIG_DTPM_CONFIGFS) += dtpm_configfs.o
 obj-$(CONFIG_DTPM_CPU) += dtpm_cpu.o
 obj-$(CONFIG_POWERCAP)	+= powercap_sys.o
 obj-$(CONFIG_INTEL_RAPL_CORE) += intel_rapl_common.o
diff --git a/drivers/powercap/dtpm_configfs.c b/drivers/powercap/dtpm_configfs.c
new file mode 100644
index 000000000000..196f8e9993da
--- /dev/null
+++ b/drivers/powercap/dtpm_configfs.c
@@ -0,0 +1,247 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021 Linaro Limited
+ *
+ * Author: Daniel Lezcano <daniel.lezcano@linaro.org>
+ *
+ * The DTPM framework defines a set of devices which are power capable.
+ *
+ * The configfs allows to create a hierarchy of devices in order
+ * to reflect the constraints we want to apply to them.
+ *
+ * Each dtpm node is created via a mkdir operation in the configfs
+ * directory. It will create the corresponding dtpm device in the
+ * sysfs and the 'device' will contain the absolute path to the dtpm
+ * node in the sysfs, thus allowing to do the connection between the
+ * created dtpm node in the configfs hierarchy and the dtpm node in
+ * the powercap framework.
+ *
+ * The dtpm nodes can be real or virtual. The former is a real device
+ * where acting on its power is possible and is registered in a dtpm
+ * framework's list with an unique name. A creation with mkdir with
+ * one of the registered name will instanciate the dtpm device. If the
+ * name is not in the registered list, it will create a virtual node
+ * where its purpose is to aggregate the power characteristics of its
+ * children which can virtual or real.
+ *
+ * It is not allowed to create a node if another one in the hierarchy
+ * has the same name. That ensures the consistency and prevents
+ * multiple instanciation of the same dtpm device.
+ */
+#include <linux/dtpm.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/configfs.h>
+
+/******************************************************************************/
+struct dtmp_configfs_nodes {
+	const char *name;
+	struct list_head node;
+};
+
+/*
+ * There is no need for a lock because the accessors are called from
+ * make and drop group which are protected by a mutex, There is the
+ * guarantee configfs ops are not called at the same time.
+ */
+static LIST_HEAD(node_list);
+
+static struct dtmp_configfs_nodes *dtmp_configfs_node_find(const char *name)
+{
+	struct dtmp_configfs_nodes *n;
+
+	list_for_each_entry(n, &node_list, node) {
+		if (!strcmp(name, n->name))
+			return n;
+	}
+
+	return NULL;
+}
+
+static int dtmp_configfs_node_add(const char *name)
+{
+	struct dtmp_configfs_nodes *n;
+
+	n = dtmp_configfs_node_find(name);
+	if (n)
+		return -EEXIST;
+
+	n = kzalloc(sizeof(*n), GFP_KERNEL);
+	if (!n)
+		return -ENOMEM;
+
+	n->name = kstrdup(name, GFP_KERNEL);
+	if (!n->name) {
+		kfree(n);
+		return -ENOMEM;
+	}
+
+	list_add_tail(&n->node, &node_list);
+
+	return 0;
+}
+
+void dtmp_configfs_node_del(const char *name)
+{
+	struct dtmp_configfs_nodes *n;
+
+	n = dtmp_configfs_node_find(name);
+	if (!n)
+		return;
+
+	list_del(&n->node);
+	kfree(n->name);
+	kfree(n);
+}
+/******************************************************************************/
+
+static struct config_group *cstrn_group;
+static struct config_item_type dtpm_cstrn_type;
+
+static struct config_group *dtpm_cstrn_make_group(struct config_group *grp, const char *name)
+{
+	struct dtpm *d, *p;
+	int ret;
+
+	/*
+	 * In order to ensure a consistency in terms of the
+	 * constraints in the hierarchy, prevent to create the same
+	 * dtpm node in different places.
+	 */
+	ret = dtmp_configfs_node_add(name);
+	if (ret)
+		return ERR_PTR(ret);
+
+	d = dtpm_get(name);
+	if (!d)
+		goto node_del;
+
+	config_group_init_type_name(&d->cfg, name, &dtpm_cstrn_type);
+
+	/*
+	 * Retrieve the dtpm parent node. The first dtpm node in the
+	 * hierarchy constraint is the root node, thus it does not
+	 * have a parent.
+	 */
+	p = (grp == cstrn_group) ? NULL :
+		container_of(grp, struct dtpm, cfg);
+
+	ret = dtpm_create(name, d, p);
+	if (ret)
+		goto dtpm_free;
+
+	if (!try_module_get(THIS_MODULE)) {
+		ret = -ENODEV;
+		goto dtpm_destroy;
+	}
+
+	return &d->cfg;
+
+dtpm_destroy:
+	dtpm_destroy(d);
+dtpm_free:
+	dtpm_put(d);
+node_del:
+	dtmp_configfs_node_del(name);
+	return ERR_PTR(ret);
+}
+
+static void dtpm_cstrn_drop_group(struct config_group *grp,
+				  struct config_item *cfg)
+{
+	struct config_group *cg = to_config_group(cfg);
+	struct dtpm *d = container_of(cg, struct dtpm, cfg);
+
+	dtmp_configfs_node_del(d->zone.name);
+	dtpm_destroy(d);
+	module_put(THIS_MODULE);
+	config_item_put(cfg);
+}
+
+static struct configfs_group_operations dtpm_cstrn_group_ops = {
+	.make_group = dtpm_cstrn_make_group,
+	.drop_item = dtpm_cstrn_drop_group,
+};
+
+static ssize_t dtpm_cstrn_device_show(struct config_item *cfg, char *str)
+{
+	struct config_group *cg = to_config_group(cfg);
+	struct dtpm *d = container_of(cg, struct dtpm, cfg);
+	struct kobject *kobj = &d->zone.dev.kobj;
+	char *string = kobject_get_path(kobj, GFP_KERNEL);
+	ssize_t len;
+
+	if (!string)
+		return -EINVAL;
+
+	len = sprintf(str, "%s\n", string);
+
+	kfree(string);
+
+	return len;
+}
+
+CONFIGFS_ATTR_RO(dtpm_cstrn_, device);
+
+static struct configfs_attribute *dtpm_cstrn_attrs[] = {
+	&dtpm_cstrn_attr_device,
+	NULL
+};
+
+static struct config_item_type dtpm_cstrn_type = {
+	.ct_owner = THIS_MODULE,
+	.ct_group_ops = &dtpm_cstrn_group_ops,
+};
+
+/******************************************************************************/
+
+static const struct config_item_type dtpm_root_group_type = {
+	.ct_owner = THIS_MODULE,
+};
+
+static struct configfs_subsystem dtpm_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = "dtpm",
+			.ci_type = &dtpm_root_group_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(dtpm_subsys.su_mutex),
+};
+
+static int __init dtpm_configfs_init(void)
+{
+	int ret;
+
+	config_group_init(&dtpm_subsys.su_group);
+
+	ret = configfs_register_subsystem(&dtpm_subsys);
+	if (ret)
+		return ret;
+
+	cstrn_group = configfs_register_default_group(&dtpm_subsys.su_group,
+						      "constraints",
+						      &dtpm_cstrn_type);
+
+	/*
+	 * The default group does not contain attributes but the other
+	 * group will
+	 */
+	dtpm_cstrn_type.ct_attrs = dtpm_cstrn_attrs;
+
+	return PTR_ERR_OR_ZERO(cstrn_group);
+}
+module_init(dtpm_configfs_init);
+
+static void __exit dtpm_configfs_exit(void)
+{
+	configfs_unregister_default_group(cstrn_group);
+	configfs_unregister_subsystem(&dtpm_subsys);
+}
+module_exit(dtpm_configfs_exit);
+
+MODULE_DESCRIPTION("DTPM configuration driver");
+MODULE_AUTHOR("Daniel Lezcano");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/dtpm.h b/include/linux/dtpm.h
index 4f7ad21291e6..6b9761aa5ea7 100644
--- a/include/linux/dtpm.h
+++ b/include/linux/dtpm.h
@@ -8,11 +8,13 @@ 
 #define ___DTPM_H__
 
 #include <linux/powercap.h>
+#include <linux/configfs.h>
 
 #define MAX_DTPM_DESCR 8
 #define MAX_DTPM_CONSTRAINTS 1
 
 struct dtpm {
+	struct config_group cfg;
 	struct powercap_zone zone;
 	struct kref kref;
 	struct dtpm *parent;