[PATCH v8 00/11] Introduce the Counter subsystem

@@ -3706,6 +3706,14 @@ W:	http://www.fi.muni.cz/~kas/cosa/
 S:	Maintained
 F:	drivers/net/wan/cosa*
 
+COUNTER SUBSYSTEM
+M:	William Breathitt Gray <vilhelm.gray@gmail.com>
+L:	linux-iio at vger.kernel.org
+S:	Maintained
+F:	drivers/counter/
+F:	include/linux/counter.h
+F:	include/linux/counter_enum.h
+
 CPMAC ETHERNET DRIVER
 M:	Florian Fainelli <f.fainelli@gmail.com>
 L:	netdev at vger.kernel.org

@@ -217,4 +217,6 @@ source "drivers/siox/Kconfig"
 
 source "drivers/slimbus/Kconfig"
 
+source "drivers/counter/Kconfig"
+
 endmenu

@@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)		+= tee/
 obj-$(CONFIG_MULTIPLEXER)	+= mux/
 obj-$(CONFIG_UNISYS_VISORBUS)	+= visorbus/
 obj-$(CONFIG_SIOX)		+= siox/
+obj-$(CONFIG_COUNTER)		+= counter/

@@ -0,0 +1,10 @@
+#
+# Counter devices
+#
+
+menuconfig COUNTER
+	tristate "Counter support"
+	help
+	  This enables counter device support through the Generic Counter
+	  interface. You only need to enable this, if you also want to enable
+	  one or more of the counter device drivers below.

@@ -0,0 +1,5 @@
+#
+# Makefile for Counter devices
+#
+
+obj-$(CONFIG_COUNTER) += counter.o

@@ -0,0 +1,1561 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic Counter interface
+ * Copyright (C) 2018 William Breathitt Gray
+ */
+#include <linux/counter.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/gfp.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+
+const char *const count_direction_str[2] = {
+	[COUNT_DIRECTION_FORWARD] = "forward",
+	[COUNT_DIRECTION_BACKWARD] = "backward"
+};
+EXPORT_SYMBOL_GPL(count_direction_str);
+
+const char *const count_mode_str[4] = {
+	[COUNT_MODE_NORMAL] = "normal",
+	[COUNT_MODE_RANGE_LIMIT] = "range limit",
+	[COUNT_MODE_NON_RECYCLE] = "non-recycle",
+	[COUNT_MODE_MODULO_N] = "modulo-n"
+};
+EXPORT_SYMBOL_GPL(count_mode_str);
+
+ssize_t counter_signal_enum_read(struct counter_device *counter,
+				 struct counter_signal *signal, void *priv,
+				 char *buf)
+{
+	const struct counter_signal_enum_ext *const e = priv;
+	int err;
+	size_t index;
+
+	if (!e->get)
+		return -EINVAL;
+
+	err = e->get(counter, signal, &index);
+	if (err)
+		return err;
+
+	if (index >= e->num_items)
+		return -EINVAL;
+
+	return sprintf(buf, "%s\n", e->items[index]);
+}
+EXPORT_SYMBOL_GPL(counter_signal_enum_read);
+
+ssize_t counter_signal_enum_write(struct counter_device *counter,
+				  struct counter_signal *signal, void *priv,
+				  const char *buf, size_t len)
+{
+	const struct counter_signal_enum_ext *const e = priv;
+	ssize_t index;
+	int err;
+
+	if (!e->set)
+		return -EINVAL;
+
+	index = __sysfs_match_string(e->items, e->num_items, buf);
+	if (index < 0)
+		return index;
+
+	err = e->set(counter, signal, index);
+	if (err)
+		return err;
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_signal_enum_write);
+
+ssize_t counter_signal_enum_available_read(struct counter_device *counter,
+					   struct counter_signal *signal,
+					   void *priv, char *buf)
+{
+	const struct counter_signal_enum_ext *const e = priv;
+	size_t i;
+	size_t len = 0;
+
+	if (!e->num_items)
+		return 0;
+
+	for (i = 0; i < e->num_items; i++)
+		len += sprintf(buf + len, "%s\n", e->items[i]);
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_signal_enum_available_read);
+
+ssize_t counter_count_enum_read(struct counter_device *counter,
+				struct counter_count *count, void *priv,
+				char *buf)
+{
+	const struct counter_count_enum_ext *const e = priv;
+	int err;
+	size_t index;
+
+	if (!e->get)
+		return -EINVAL;
+
+	err = e->get(counter, count, &index);
+	if (err)
+		return err;
+
+	if (index >= e->num_items)
+		return -EINVAL;
+
+	return sprintf(buf, "%s\n", e->items[index]);
+}
+EXPORT_SYMBOL_GPL(counter_count_enum_read);
+
+ssize_t counter_count_enum_write(struct counter_device *counter,
+				 struct counter_count *count, void *priv,
+				 const char *buf, size_t len)
+{
+	const struct counter_count_enum_ext *const e = priv;
+	ssize_t index;
+	int err;
+
+	if (!e->set)
+		return -EINVAL;
+
+	index = __sysfs_match_string(e->items, e->num_items, buf);
+	if (index < 0)
+		return index;
+
+	err = e->set(counter, count, index);
+	if (err)
+		return err;
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_count_enum_write);
+
+ssize_t counter_count_enum_available_read(struct counter_device *counter,
+					  struct counter_count *count,
+					  void *priv, char *buf)
+{
+	const struct counter_count_enum_ext *const e = priv;
+	size_t i;
+	size_t len = 0;
+
+	if (!e->num_items)
+		return 0;
+
+	for (i = 0; i < e->num_items; i++)
+		len += sprintf(buf + len, "%s\n", e->items[i]);
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_count_enum_available_read);
+
+ssize_t counter_device_enum_read(struct counter_device *counter, void *priv,
+				 char *buf)
+{
+	const struct counter_device_enum_ext *const e = priv;
+	int err;
+	size_t index;
+
+	if (!e->get)
+		return -EINVAL;
+
+	err = e->get(counter, &index);
+	if (err)
+		return err;
+
+	if (index >= e->num_items)
+		return -EINVAL;
+
+	return sprintf(buf, "%s\n", e->items[index]);
+}
+EXPORT_SYMBOL_GPL(counter_device_enum_read);
+
+ssize_t counter_device_enum_write(struct counter_device *counter, void *priv,
+				  const char *buf, size_t len)
+{
+	const struct counter_device_enum_ext *const e = priv;
+	ssize_t index;
+	int err;
+
+	if (!e->set)
+		return -EINVAL;
+
+	index = __sysfs_match_string(e->items, e->num_items, buf);
+	if (index < 0)
+		return index;
+
+	err = e->set(counter, index);
+	if (err)
+		return err;
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_device_enum_write);
+
+ssize_t counter_device_enum_available_read(struct counter_device *counter,
+					   void *priv, char *buf)
+{
+	const struct counter_device_enum_ext *const e = priv;
+	size_t i;
+	size_t len = 0;
+
+	if (!e->num_items)
+		return 0;
+
+	for (i = 0; i < e->num_items; i++)
+		len += sprintf(buf + len, "%s\n", e->items[i]);
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(counter_device_enum_available_read);
+
+static const char *const signal_level_str[] = {
+	[SIGNAL_LEVEL_LOW] = "low",
+	[SIGNAL_LEVEL_HIGH] = "high"
+};
+
+/**
+ * signal_read_value_set - set signal_read_value data
+ * @val:	signal_read_value structure to set
+ * @type:	property Signal data represents
+ * @data:	Signal data
+ *
+ * This function sets an opaque signal_read_value structure with the provided
+ * Signal data.
+ */
+void signal_read_value_set(struct signal_read_value *const val,
+			   const enum signal_value_type type, void *const data)
+{
+	if (type == SIGNAL_LEVEL)
+		val->len = sprintf(val->buf, "%s\n",
+			signal_level_str[*(enum signal_level *)data]);
+	else
+		val->len = 0;
+}
+EXPORT_SYMBOL_GPL(signal_read_value_set);
+
+/**
+ * count_read_value_set - set count_read_value data
+ * @val:	count_read_value structure to set
+ * @type:	property Count data represents
+ * @data:	Count data
+ *
+ * This function sets an opaque count_read_value structure with the provided
+ * Count data.
+ */
+void count_read_value_set(struct count_read_value *const val,
+			  const enum count_value_type type, void *const data)
+{
+	switch (type) {
+	case COUNT_POSITION:
+		val->len = sprintf(val->buf, "%lu\n", *(unsigned long *)data);
+		break;
+	default:
+		val->len = 0;
+	}
+}
+EXPORT_SYMBOL_GPL(count_read_value_set);
+
+/**
+ * count_write_value_get - get count_write_value data
+ * @data:	Count data
+ * @type:	property Count data represents
+ * @val:	count_write_value structure containing data
+ *
+ * This function extracts Count data from the provided opaque count_write_value
+ * structure and stores it at the address provided by @data.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int count_write_value_get(void *const data, const enum count_value_type type,
+			  const struct count_write_value *const val)
+{
+	int err;
+
+	switch (type) {
+	case COUNT_POSITION:
+		err = kstrtoul(val->buf, 0, data);
+		if (err)
+			return err;
+		break;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(count_write_value_get);
+
+struct counter_attr_parm {
+	struct counter_device_attr_group *group;
+	const char *prefix;
+	const char *name;
+	ssize_t (*show)(struct device *dev, struct device_attribute *attr,
+			char *buf);
+	ssize_t (*store)(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t len);
+	void *component;
+};
+
+struct counter_device_attr {
+	struct device_attribute		dev_attr;
+	struct list_head		l;
+	void				*component;
+};
+
+static int counter_attribute_create(const struct counter_attr_parm *const parm)
+{
+	struct counter_device_attr *counter_attr;
+	struct device_attribute *dev_attr;
+	int err;
+	struct list_head *const attr_list = &parm->group->attr_list;
+
+	/* Allocate a Counter device attribute */
+	counter_attr = kzalloc(sizeof(*counter_attr), GFP_KERNEL);
+	if (!counter_attr)
+		return -ENOMEM;
+	dev_attr = &counter_attr->dev_attr;
+
+	sysfs_attr_init(&dev_attr->attr);
+
+	/* Configure device attribute */
+	dev_attr->attr.name = kasprintf(GFP_KERNEL, "%s%s", parm->prefix,
+					parm->name);
+	if (!dev_attr->attr.name) {
+		err = -ENOMEM;
+		goto err_free_counter_attr;
+	}
+	if (parm->show) {
+		dev_attr->attr.mode |= 0444;
+		dev_attr->show = parm->show;
+	}
+	if (parm->store) {
+		dev_attr->attr.mode |= 0200;
+		dev_attr->store = parm->store;
+	}
+
+	/* Store associated Counter component with attribute */
+	counter_attr->component = parm->component;
+
+	/* Keep track of the attribute for later cleanup */
+	list_add(&counter_attr->l, attr_list);
+	parm->group->num_attr++;
+
+	return 0;
+
+err_free_counter_attr:
+	kfree(counter_attr);
+	return err;
+}
+
+#define to_counter_attr(_dev_attr) \
+	container_of(_dev_attr, struct counter_device_attr, dev_attr)
+
+struct signal_unit {
+	struct counter_signal	*signal;
+};
+
+static ssize_t counter_signal_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct signal_unit *const component = devattr->component;
+	struct counter_signal *const signal = component->signal;
+	int err;
+	struct signal_read_value val = { .buf = buf };
+
+	err = counter->ops->signal_read(counter, signal, &val);
+	if (err)
+		return err;
+
+	return val.len;
+}
+
+struct name_unit {
+	const char	*name;
+};
+
+static ssize_t counter_device_attr_name_show(struct device *dev,
+					     struct device_attribute *attr,
+					     char *buf)
+{
+	const struct name_unit *const comp = to_counter_attr(attr)->component;
+
+	return sprintf(buf, "%s\n", comp->name);
+}
+
+static int counter_name_attribute_create(
+	struct counter_device_attr_group *const group,
+	const char *const name)
+{
+	struct name_unit *name_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Skip if no name */
+	if (!name)
+		return 0;
+
+	/* Allocate name attribute component */
+	name_comp = kmalloc(sizeof(*name_comp), GFP_KERNEL);
+	if (!name_comp)
+		return -ENOMEM;
+	name_comp->name = name;
+
+	/* Allocate Signal name attribute */
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = "name";
+	parm.show = counter_device_attr_name_show;
+	parm.store = NULL;
+	parm.component = name_comp;
+	err = counter_attribute_create(&parm);
+	if (err)
+		goto err_free_name_comp;
+
+	return 0;
+
+err_free_name_comp:
+	kfree(name_comp);
+	return err;
+}
+
+struct signal_ext_unit {
+	struct counter_signal		*signal;
+	const struct counter_signal_ext	*ext;
+};
+
+static ssize_t counter_signal_ext_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct signal_ext_unit *const comp = devattr->component;
+	const struct counter_signal_ext *const ext = comp->ext;
+
+	return ext->read(dev_get_drvdata(dev), comp->signal, ext->priv, buf);
+}
+
+static ssize_t counter_signal_ext_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t len)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct signal_ext_unit *const comp = devattr->component;
+	const struct counter_signal_ext *const ext = comp->ext;
+
+	return ext->write(dev_get_drvdata(dev), comp->signal, ext->priv, buf,
+		len);
+}
+
+static void counter_device_attr_list_free(struct list_head *attr_list)
+{
+	struct counter_device_attr *p, *n;
+
+	list_for_each_entry_safe(p, n, attr_list, l) {
+		/* free attribute name and associated component memory */
+		kfree(p->dev_attr.attr.name);
+		kfree(p->component);
+		list_del(&p->l);
+		kfree(p);
+	}
+}
+
+static int counter_signal_ext_register(
+	struct counter_device_attr_group *const group,
+	struct counter_signal *const signal)
+{
+	const size_t num_ext = signal->num_ext;
+	size_t i;
+	const struct counter_signal_ext *ext;
+	struct signal_ext_unit *signal_ext_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Create an attribute for each extension */
+	for (i = 0 ; i < num_ext; i++) {
+		ext = signal->ext + i;
+
+		/* Allocate signal_ext attribute component */
+		signal_ext_comp = kmalloc(sizeof(*signal_ext_comp), GFP_KERNEL);
+		if (!signal_ext_comp) {
+			err = -ENOMEM;
+			goto err_free_attr_list;
+		}
+		signal_ext_comp->signal = signal;
+		signal_ext_comp->ext = ext;
+
+		/* Allocate a Counter device attribute */
+		parm.group = group;
+		parm.prefix = "";
+		parm.name = ext->name;
+		parm.show = (ext->read) ? counter_signal_ext_show : NULL;
+		parm.store = (ext->write) ? counter_signal_ext_store : NULL;
+		parm.component = signal_ext_comp;
+		err = counter_attribute_create(&parm);
+		if (err) {
+			kfree(signal_ext_comp);
+			goto err_free_attr_list;
+		}
+	}
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+static int counter_signal_attributes_create(
+	struct counter_device_attr_group *const group,
+	const struct counter_device *const counter,
+	struct counter_signal *const signal)
+{
+	struct signal_unit *signal_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Allocate Signal attribute component */
+	signal_comp = kmalloc(sizeof(*signal_comp), GFP_KERNEL);
+	if (!signal_comp)
+		return -ENOMEM;
+	signal_comp->signal = signal;
+
+	/* Create main Signal attribute */
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = "signal";
+	parm.show = (counter->ops->signal_read) ? counter_signal_show : NULL;
+	parm.store = NULL;
+	parm.component = signal_comp;
+	err = counter_attribute_create(&parm);
+	if (err) {
+		kfree(signal_comp);
+		return err;
+	}
+
+	/* Create Signal name attribute */
+	err = counter_name_attribute_create(group, signal->name);
+	if (err)
+		goto err_free_attr_list;
+
+	/* Register Signal extension attributes */
+	err = counter_signal_ext_register(group, signal);
+	if (err)
+		goto err_free_attr_list;
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+static int counter_signals_register(
+	struct counter_device_attr_group *const groups_list,
+	const struct counter_device *const counter)
+{
+	const size_t num_signals = counter->num_signals;
+	size_t i;
+	struct counter_signal *signal;
+	const char *name;
+	int err;
+
+	/* Register each Signal */
+	for (i = 0; i < num_signals; i++) {
+		signal = counter->signals + i;
+
+		/* Generate Signal attribute directory name */
+		name = kasprintf(GFP_KERNEL, "signal%d", signal->id);
+		if (!name) {
+			err = -ENOMEM;
+			goto err_free_attr_groups;
+		}
+		groups_list[i].attr_group.name = name;
+
+		/* Create all attributes associated with Signal */
+		err = counter_signal_attributes_create(groups_list + i, counter,
+						       signal);
+		if (err)
+			goto err_free_attr_groups;
+	}
+
+	return 0;
+
+err_free_attr_groups:
+	do {
+		kfree(groups_list[i].attr_group.name);
+		counter_device_attr_list_free(&groups_list[i].attr_list);
+	} while (i--);
+	return err;
+}
+
+static const char *const synapse_action_str[] = {
+	[SYNAPSE_ACTION_NONE] = "none",
+	[SYNAPSE_ACTION_RISING_EDGE] = "rising edge",
+	[SYNAPSE_ACTION_FALLING_EDGE] = "falling edge",
+	[SYNAPSE_ACTION_BOTH_EDGES] = "both edges"
+};
+
+struct action_unit {
+	struct counter_synapse	*synapse;
+	struct counter_count	*count;
+};
+
+static ssize_t counter_action_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	int err;
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	const struct action_unit *const component = devattr->component;
+	struct counter_count *const count = component->count;
+	struct counter_synapse *const synapse = component->synapse;
+	size_t action_index;
+	enum synapse_action action;
+
+	err = counter->ops->action_get(counter, count, synapse, &action_index);
+	if (err)
+		return err;
+
+	synapse->action = action_index;
+
+	action = synapse->actions_list[action_index];
+	return sprintf(buf, "%s\n", synapse_action_str[action]);
+}
+
+static ssize_t counter_action_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf, size_t len)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct action_unit *const component = devattr->component;
+	struct counter_synapse *const synapse = component->synapse;
+	size_t action_index;
+	const size_t num_actions = synapse->num_actions;
+	enum synapse_action action;
+	int err;
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	struct counter_count *const count = component->count;
+
+	/* Find requested action mode */
+	for (action_index = 0; action_index < num_actions; action_index++) {
+		action = synapse->actions_list[action_index];
+		if (sysfs_streq(buf, synapse_action_str[action]))
+			break;
+	}
+	/* If requested action mode not found */
+	if (action_index >= num_actions)
+		return -EINVAL;
+
+	err = counter->ops->action_set(counter, count, synapse, action_index);
+	if (err)
+		return err;
+
+	synapse->action = action_index;
+
+	return len;
+}
+
+struct action_avail_unit {
+	const enum synapse_action	*actions_list;
+	size_t				num_actions;
+};
+
+static ssize_t counter_synapse_action_available_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct action_avail_unit *const component = devattr->component;
+	size_t i;
+	enum synapse_action action;
+	ssize_t len = 0;
+
+	for (i = 0; i < component->num_actions; i++) {
+		action = component->actions_list[i];
+		len += sprintf(buf + len, "%s\n", synapse_action_str[action]);
+	}
+
+	return len;
+}
+
+static int counter_synapses_register(
+	struct counter_device_attr_group *const group,
+	const struct counter_device *const counter,
+	struct counter_count *const count, const char *const count_attr_name)
+{
+	size_t i;
+	struct counter_synapse *synapse;
+	const char *prefix;
+	struct action_unit *action_comp;
+	struct counter_attr_parm parm;
+	int err;
+	struct action_avail_unit *avail_comp;
+
+	/* Register each Synapse */
+	for (i = 0; i < count->num_synapses; i++) {
+		synapse = count->synapses + i;
+
+		/* Generate attribute prefix */
+		prefix = kasprintf(GFP_KERNEL, "signal%d_",
+				   synapse->signal->id);
+		if (!prefix) {
+			err = -ENOMEM;
+			goto err_free_attr_list;
+		}
+
+		/* Allocate action attribute component */
+		action_comp = kmalloc(sizeof(*action_comp), GFP_KERNEL);
+		if (!action_comp) {
+			err = -ENOMEM;
+			goto err_free_prefix;
+		}
+		action_comp->synapse = synapse;
+		action_comp->count = count;
+
+		/* Create action attribute */
+		parm.group = group;
+		parm.prefix = prefix;
+		parm.name = "action";
+		parm.show = (counter->ops->action_get) ? counter_action_show : NULL;
+		parm.store = (counter->ops->action_set) ? counter_action_store : NULL;
+		parm.component = action_comp;
+		err = counter_attribute_create(&parm);
+		if (err) {
+			kfree(action_comp);
+			goto err_free_prefix;
+		}
+
+		/* Allocate action available attribute component */
+		avail_comp = kmalloc(sizeof(*avail_comp), GFP_KERNEL);
+		if (!avail_comp) {
+			err = -ENOMEM;
+			goto err_free_prefix;
+		}
+		avail_comp->actions_list = synapse->actions_list;
+		avail_comp->num_actions = synapse->num_actions;
+
+		/* Create action_available attribute */
+		parm.group = group;
+		parm.prefix = prefix;
+		parm.name = "action_available";
+		parm.show = counter_synapse_action_available_show;
+		parm.store = NULL;
+		parm.component = avail_comp;
+		err = counter_attribute_create(&parm);
+		if (err) {
+			kfree(avail_comp);
+			goto err_free_prefix;
+		}
+
+		kfree(prefix);
+	}
+
+	return 0;
+
+err_free_prefix:
+	kfree(prefix);
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+struct count_unit {
+	struct counter_count	*count;
+};
+
+static ssize_t counter_count_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_unit *const component = devattr->component;
+	struct counter_count *const count = component->count;
+	int err;
+	struct count_read_value val = { .buf = buf };
+
+	err = counter->ops->count_read(counter, count, &val);
+	if (err)
+		return err;
+
+	return val.len;
+}
+
+static ssize_t counter_count_store(struct device *dev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t len)
+{
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_unit *const component = devattr->component;
+	struct counter_count *const count = component->count;
+	int err;
+	struct count_write_value val = { .buf = buf };
+
+	err = counter->ops->count_write(counter, count, &val);
+	if (err)
+		return err;
+
+	return len;
+}
+
+static const char *const count_function_str[] = {
+	[COUNT_FUNCTION_INCREASE] = "increase",
+	[COUNT_FUNCTION_DECREASE] = "decrease",
+	[COUNT_FUNCTION_PULSE_DIRECTION] = "pulse-direction",
+	[COUNT_FUNCTION_QUADRATURE_X1_A] = "quadrature x1 a",
+	[COUNT_FUNCTION_QUADRATURE_X1_B] = "quadrature x1 b",
+	[COUNT_FUNCTION_QUADRATURE_X2_A] = "quadrature x2 a",
+	[COUNT_FUNCTION_QUADRATURE_X2_B] = "quadrature x2 b",
+	[COUNT_FUNCTION_QUADRATURE_X4] = "quadrature x4"
+};
+
+static ssize_t counter_function_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	int err;
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_unit *const component = devattr->component;
+	struct counter_count *const count = component->count;
+	size_t func_index;
+	enum count_function function;
+
+	err = counter->ops->function_get(counter, count, &func_index);
+	if (err)
+		return err;
+
+	count->function = func_index;
+
+	function = count->functions_list[func_index];
+	return sprintf(buf, "%s\n", count_function_str[function]);
+}
+
+static ssize_t counter_function_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t len)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_unit *const component = devattr->component;
+	struct counter_count *const count = component->count;
+	const size_t num_functions = count->num_functions;
+	size_t func_index;
+	enum count_function function;
+	int err;
+	struct counter_device *const counter = dev_get_drvdata(dev);
+
+	/* Find requested Count function mode */
+	for (func_index = 0; func_index < num_functions; func_index++) {
+		function = count->functions_list[func_index];
+		if (sysfs_streq(buf, count_function_str[function]))
+			break;
+	}
+	/* Return error if requested Count function mode not found */
+	if (func_index >= num_functions)
+		return -EINVAL;
+
+	err = counter->ops->function_set(counter, count, func_index);
+	if (err)
+		return err;
+
+	count->function = func_index;
+
+	return len;
+}
+
+struct count_ext_unit {
+	struct counter_count		*count;
+	const struct counter_count_ext	*ext;
+};
+
+static ssize_t counter_count_ext_show(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_ext_unit *const comp = devattr->component;
+	const struct counter_count_ext *const ext = comp->ext;
+
+	return ext->read(dev_get_drvdata(dev), comp->count, ext->priv, buf);
+}
+
+static ssize_t counter_count_ext_store(struct device *dev,
+				       struct device_attribute *attr,
+				       const char *buf, size_t len)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct count_ext_unit *const comp = devattr->component;
+	const struct counter_count_ext *const ext = comp->ext;
+
+	return ext->write(dev_get_drvdata(dev), comp->count, ext->priv, buf,
+		len);
+}
+
+static int counter_count_ext_register(
+	struct counter_device_attr_group *const group,
+	struct counter_count *const count)
+{
+	size_t i;
+	const struct counter_count_ext *ext;
+	struct count_ext_unit *count_ext_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Create an attribute for each extension */
+	for (i = 0 ; i < count->num_ext; i++) {
+		ext = count->ext + i;
+
+		/* Allocate count_ext attribute component */
+		count_ext_comp = kmalloc(sizeof(*count_ext_comp), GFP_KERNEL);
+		if (!count_ext_comp) {
+			err = -ENOMEM;
+			goto err_free_attr_list;
+		}
+		count_ext_comp->count = count;
+		count_ext_comp->ext = ext;
+
+		/* Allocate count_ext attribute */
+		parm.group = group;
+		parm.prefix = "";
+		parm.name = ext->name;
+		parm.show = (ext->read) ? counter_count_ext_show : NULL;
+		parm.store = (ext->write) ? counter_count_ext_store : NULL;
+		parm.component = count_ext_comp;
+		err = counter_attribute_create(&parm);
+		if (err) {
+			kfree(count_ext_comp);
+			goto err_free_attr_list;
+		}
+	}
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+struct func_avail_unit {
+	const enum count_function	*functions_list;
+	size_t				num_functions;
+};
+
+static ssize_t counter_count_function_available_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct func_avail_unit *const component = devattr->component;
+	const enum count_function *const func_list = component->functions_list;
+	const size_t num_functions = component->num_functions;
+	size_t i;
+	enum count_function function;
+	ssize_t len = 0;
+
+	for (i = 0; i < num_functions; i++) {
+		function = func_list[i];
+		len += sprintf(buf + len, "%s\n", count_function_str[function]);
+	}
+
+	return len;
+}
+
+static int counter_count_attributes_create(
+	struct counter_device_attr_group *const group,
+	const struct counter_device *const counter,
+	struct counter_count *const count)
+{
+	struct count_unit *count_comp;
+	struct counter_attr_parm parm;
+	int err;
+	struct count_unit *func_comp;
+	struct func_avail_unit *avail_comp;
+
+	/* Allocate count attribute component */
+	count_comp = kmalloc(sizeof(*count_comp), GFP_KERNEL);
+	if (!count_comp)
+		return -ENOMEM;
+	count_comp->count = count;
+
+	/* Create main Count attribute */
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = "count";
+	parm.show = (counter->ops->count_read) ? counter_count_show : NULL;
+	parm.store = (counter->ops->count_write) ? counter_count_store : NULL;
+	parm.component = count_comp;
+	err = counter_attribute_create(&parm);
+	if (err) {
+		kfree(count_comp);
+		return err;
+	}
+
+	/* Allocate function attribute component */
+	func_comp = kmalloc(sizeof(*func_comp), GFP_KERNEL);
+	if (!func_comp) {
+		err = -ENOMEM;
+		goto err_free_attr_list;
+	}
+	func_comp->count = count;
+
+	/* Create Count function attribute */
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = "function";
+	parm.show = (counter->ops->function_get) ? counter_function_show : NULL;
+	parm.store = (counter->ops->function_set) ? counter_function_store : NULL;
+	parm.component = func_comp;
+	err = counter_attribute_create(&parm);
+	if (err) {
+		kfree(func_comp);
+		goto err_free_attr_list;
+	}
+
+	/* Allocate function available attribute component */
+	avail_comp = kmalloc(sizeof(*avail_comp), GFP_KERNEL);
+	if (!avail_comp) {
+		err = -ENOMEM;
+		goto err_free_attr_list;
+	}
+	avail_comp->functions_list = count->functions_list;
+	avail_comp->num_functions = count->num_functions;
+
+	/* Create Count function_available attribute */
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = "function_available";
+	parm.show = counter_count_function_available_show;
+	parm.store = NULL;
+	parm.component = avail_comp;
+	err = counter_attribute_create(&parm);
+	if (err) {
+		kfree(avail_comp);
+		goto err_free_attr_list;
+	}
+
+	/* Create Count name attribute */
+	err = counter_name_attribute_create(group, count->name);
+	if (err)
+		goto err_free_attr_list;
+
+	/* Register Count extension attributes */
+	err = counter_count_ext_register(group, count);
+	if (err)
+		goto err_free_attr_list;
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+static int counter_counts_register(
+	struct counter_device_attr_group *const groups_list,
+	const struct counter_device *const counter)
+{
+	size_t i;
+	struct counter_count *count;
+	const char *name;
+	int err;
+
+	/* Register each Count */
+	for (i = 0; i < counter->num_counts; i++) {
+		count = counter->counts + i;
+
+		/* Generate Count attribute directory name */
+		name = kasprintf(GFP_KERNEL, "count%d", count->id);
+		if (!name) {
+			err = -ENOMEM;
+			goto err_free_attr_groups;
+		}
+		groups_list[i].attr_group.name = name;
+
+		/* Register the Synapses associated with each Count */
+		err = counter_synapses_register(groups_list + i, counter, count,
+						name);
+		if (err)
+			goto err_free_attr_groups;
+
+		/* Create all attributes associated with Count */
+		err = counter_count_attributes_create(groups_list + i, counter,
+						      count);
+		if (err)
+			goto err_free_attr_groups;
+	}
+
+	return 0;
+
+err_free_attr_groups:
+	do {
+		kfree(groups_list[i].attr_group.name);
+		counter_device_attr_list_free(&groups_list[i].attr_list);
+	} while (i--);
+	return err;
+}
+
+struct size_unit {
+	size_t size;
+};
+
+static ssize_t counter_device_attr_size_show(struct device *dev,
+					     struct device_attribute *attr,
+					     char *buf)
+{
+	const struct size_unit *const comp = to_counter_attr(attr)->component;
+
+	return sprintf(buf, "%zu\n", comp->size);
+}
+
+static int counter_size_attribute_create(
+	struct counter_device_attr_group *const group,
+	const size_t size, const char *const name)
+{
+	struct size_unit *size_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Allocate size attribute component */
+	size_comp = kmalloc(sizeof(*size_comp), GFP_KERNEL);
+	if (!size_comp)
+		return -ENOMEM;
+	size_comp->size = size;
+
+	parm.group = group;
+	parm.prefix = "";
+	parm.name = name;
+	parm.show = counter_device_attr_size_show;
+	parm.store = NULL;
+	parm.component = size_comp;
+	err = counter_attribute_create(&parm);
+	if (err)
+		goto err_free_size_comp;
+
+	return 0;
+
+err_free_size_comp:
+	kfree(size_comp);
+	return err;
+}
+
+struct ext_unit {
+	const struct counter_device_ext	*ext;
+};
+
+static ssize_t counter_device_ext_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct ext_unit *const component = devattr->component;
+	const struct counter_device_ext *const ext = component->ext;
+
+	return ext->read(dev_get_drvdata(dev), ext->priv, buf);
+}
+
+static ssize_t counter_device_ext_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t len)
+{
+	const struct counter_device_attr *const devattr = to_counter_attr(attr);
+	const struct ext_unit *const component = devattr->component;
+	const struct counter_device_ext *const ext = component->ext;
+
+	return ext->write(dev_get_drvdata(dev), ext->priv, buf, len);
+}
+
+static int counter_device_ext_register(
+	struct counter_device_attr_group *const group,
+	struct counter_device *const counter)
+{
+	size_t i;
+	struct ext_unit *ext_comp;
+	struct counter_attr_parm parm;
+	int err;
+
+	/* Create an attribute for each extension */
+	for (i = 0 ; i < counter->num_ext; i++) {
+		/* Allocate extension attribute component */
+		ext_comp = kmalloc(sizeof(*ext_comp), GFP_KERNEL);
+		if (!ext_comp) {
+			err = -ENOMEM;
+			goto err_free_attr_list;
+		}
+
+		ext_comp->ext = counter->ext + i;
+
+		/* Allocate extension attribute */
+		parm.group = group;
+		parm.prefix = "";
+		parm.name = counter->ext[i].name;
+		parm.show = (counter->ext[i].read) ? counter_device_ext_show : NULL;
+		parm.store = (counter->ext[i].write) ? counter_device_ext_store : NULL;
+		parm.component = ext_comp;
+		err = counter_attribute_create(&parm);
+		if (err) {
+			kfree(ext_comp);
+			goto err_free_attr_list;
+		}
+	}
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+static int counter_global_attr_register(
+	struct counter_device_attr_group *const group,
+	struct counter_device *const counter)
+{
+	int err;
+
+	/* Create name attribute */
+	err = counter_name_attribute_create(group, counter->name);
+	if (err)
+		return err;
+
+	/* Create num_counts attribute */
+	err = counter_size_attribute_create(group, counter->num_counts,
+					    "num_counts");
+	if (err)
+		goto err_free_attr_list;
+
+	/* Create num_signals attribute */
+	err = counter_size_attribute_create(group, counter->num_signals,
+					    "num_signals");
+	if (err)
+		goto err_free_attr_list;
+
+	/* Register Counter device extension attributes */
+	err = counter_device_ext_register(group, counter);
+	if (err)
+		goto err_free_attr_list;
+
+	return 0;
+
+err_free_attr_list:
+	counter_device_attr_list_free(&group->attr_list);
+	return err;
+}
+
+static void counter_device_groups_list_free(
+	struct counter_device_attr_group *const groups_list,
+	const size_t num_groups)
+{
+	struct counter_device_attr_group *group;
+	size_t i;
+
+	/* loop through all attribute groups (signals, counts, global, etc.) */
+	for (i = 0; i < num_groups; i++) {
+		group = groups_list + i;
+
+		/* free all attribute group and associated attributes memory */
+		kfree(group->attr_group.name);
+		kfree(group->attr_group.attrs);
+		counter_device_attr_list_free(&group->attr_list);
+	}
+
+	kfree(groups_list);
+}
+
+static int counter_device_groups_list_prepare(
+	struct counter_device *const counter)
+{
+	const size_t total_num_groups =
+		counter->num_signals + counter->num_counts + 1;
+	struct counter_device_attr_group *groups_list;
+	size_t i;
+	int err;
+	size_t num_groups = 0;
+
+	/* Allocate space for attribute groups (signals, counts, and ext) */
+	groups_list = kcalloc(total_num_groups, sizeof(*groups_list),
+			      GFP_KERNEL);
+	if (!groups_list)
+		return -ENOMEM;
+
+	/* Initialize attribute lists */
+	for (i = 0; i < total_num_groups; i++)
+		INIT_LIST_HEAD(&groups_list[i].attr_list);
+
+	/* Register Signals */
+	err = counter_signals_register(groups_list, counter);
+	if (err)
+		goto err_free_groups_list;
+	num_groups += counter->num_signals;
+
+	/* Register Counts and respective Synapses */
+	err = counter_counts_register(groups_list + num_groups, counter);
+	if (err)
+		goto err_free_groups_list;
+	num_groups += counter->num_counts;
+
+	/* Register Counter global attributes */
+	err = counter_global_attr_register(groups_list + num_groups, counter);
+	if (err)
+		goto err_free_groups_list;
+	num_groups++;
+
+	/* Store groups_list in device_state */
+	counter->device_state->groups_list = groups_list;
+	counter->device_state->num_groups = num_groups;
+
+	return 0;
+
+err_free_groups_list:
+	counter_device_groups_list_free(groups_list, num_groups);
+	return err;
+}
+
+static int counter_device_groups_prepare(
+	struct counter_device_state *const device_state)
+{
+	size_t i, j;
+	struct counter_device_attr_group *group;
+	int err;
+	struct counter_device_attr *p;
+
+	/* Allocate attribute groups for association with device */
+	device_state->groups = kcalloc(device_state->num_groups + 1,
+				       sizeof(*device_state->groups),
+				       GFP_KERNEL);
+	if (!device_state->groups)
+		return -ENOMEM;
+
+	/* Prepare each group of attributes for association */
+	for (i = 0; i < device_state->num_groups; i++) {
+		group = device_state->groups_list + i;
+
+		/* Allocate space for attribute pointers in attribute group */
+		group->attr_group.attrs = kcalloc(group->num_attr + 1,
+			sizeof(*group->attr_group.attrs), GFP_KERNEL);
+		if (!group->attr_group.attrs) {
+			err = -ENOMEM;
+			goto err_free_groups;
+		}
+
+		/* Add attribute pointers to attribute group */
+		j = 0;
+		list_for_each_entry(p, &group->attr_list, l)
+			group->attr_group.attrs[j++] = &p->dev_attr.attr;
+
+		/* Group attributes in attribute group */
+		device_state->groups[i] = &group->attr_group;
+	}
+	/* Associate attributes with device */
+	device_state->dev.groups = device_state->groups;
+
+	return 0;
+
+err_free_groups:
+	do {
+		group = device_state->groups_list + i;
+		kfree(group->attr_group.attrs);
+		group->attr_group.attrs = NULL;
+	} while (i--);
+	kfree(device_state->groups);
+	return err;
+}
+
+/* Provides a unique ID for each counter device */
+static DEFINE_IDA(counter_ida);
+
+static void counter_device_release(struct device *dev)
+{
+	struct counter_device *const counter = dev_get_drvdata(dev);
+	struct counter_device_state *const device_state = counter->device_state;
+
+	kfree(device_state->groups);
+	counter_device_groups_list_free(device_state->groups_list,
+					device_state->num_groups);
+	ida_simple_remove(&counter_ida, device_state->id);
+	kfree(device_state);
+}
+
+static struct device_type counter_device_type = {
+	.name = "counter_device",
+	.release = counter_device_release
+};
+
+static struct bus_type counter_bus_type = {
+	.name = "counter"
+};
+
+/**
+ * counter_register - register Counter to the system
+ * @counter:	pointer to Counter to register
+ *
+ * This function registers a Counter to the system. A sysfs "counter" directory
+ * will be created and populated with sysfs attributes correlating with the
+ * Counter Signals, Synapses, and Counts respectively.
+ */
+int counter_register(struct counter_device *const counter)
+{
+	struct counter_device_state *device_state;
+	int err;
+
+	/* Allocate internal state container for Counter device */
+	device_state = kzalloc(sizeof(*device_state), GFP_KERNEL);
+	if (!device_state)
+		return -ENOMEM;
+	counter->device_state = device_state;
+
+	/* Acquire unique ID */
+	device_state->id = ida_simple_get(&counter_ida, 0, 0, GFP_KERNEL);
+	if (device_state->id < 0) {
+		err = device_state->id;
+		goto err_free_device_state;
+	}
+
+	/* Configure device structure for Counter */
+	device_state->dev.type = &counter_device_type;
+	device_state->dev.bus = &counter_bus_type;
+	if (counter->parent) {
+		device_state->dev.parent = counter->parent;
+		device_state->dev.of_node = counter->parent->of_node;
+	}
+	dev_set_name(&device_state->dev, "counter%d", device_state->id);
+	device_initialize(&device_state->dev);
+	dev_set_drvdata(&device_state->dev, counter);
+
+	/* Prepare device attributes */
+	err = counter_device_groups_list_prepare(counter);
+	if (err)
+		goto err_free_id;
+
+	/* Organize device attributes to groups and match to device */
+	err = counter_device_groups_prepare(device_state);
+	if (err)
+		goto err_free_groups_list;
+
+	/* Add device to system */
+	err = device_add(&device_state->dev);
+	if (err)
+		goto err_free_groups;
+
+	return 0;
+
+err_free_groups:
+	kfree(device_state->groups);
+err_free_groups_list:
+	counter_device_groups_list_free(device_state->groups_list,
+					device_state->num_groups);
+err_free_id:
+	ida_simple_remove(&counter_ida, device_state->id);
+err_free_device_state:
+	kfree(device_state);
+	return err;
+}
+EXPORT_SYMBOL_GPL(counter_register);
+
+/**
+ * counter_unregister - unregister Counter from the system
+ * @counter:	pointer to Counter to unregister
+ *
+ * The Counter is unregistered from the system; all allocated memory is freed.
+ */
+void counter_unregister(struct counter_device *const counter)
+{
+	if (counter)
+		device_del(&counter->device_state->dev);
+}
+EXPORT_SYMBOL_GPL(counter_unregister);
+
+static void devm_counter_unreg(struct device *dev, void *res)
+{
+	counter_unregister(*(struct counter_device **)res);
+}
+
+/**
+ * devm_counter_register - Resource-managed counter_register
+ * @dev:	device to allocate counter_device for
+ * @counter:	pointer to Counter to register
+ *
+ * Managed counter_register. The Counter registered with this function is
+ * automatically unregistered on driver detach. This function calls
+ * counter_register internally. Refer to that function for more information.
+ *
+ * If an Counter registered with this function needs to be unregistered
+ * separately, devm_counter_unregister must be used.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_counter_register(struct device *dev,
+			  struct counter_device *const counter)
+{
+	struct counter_device **ptr;
+	int ret;
+
+	ptr = devres_alloc(devm_counter_unreg, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return -ENOMEM;
+
+	ret = counter_register(counter);
+	if (!ret) {
+		*ptr = counter;
+		devres_add(dev, ptr);
+	} else {
+		devres_free(ptr);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(devm_counter_register);
+
+static int devm_counter_match(struct device *dev, void *res, void *data)
+{
+	struct counter_device **r = res;
+
+	if (!r || !*r) {
+		WARN_ON(!r || !*r);
+		return 0;
+	}
+
+	return *r == data;
+}
+
+/**
+ * devm_counter_unregister - Resource-managed counter_unregister
+ * @dev:	device this counter_device belongs to
+ * @counter:	pointer to Counter associated with the device
+ *
+ * Unregister Counter registered with devm_counter_register.
+ */
+void devm_counter_unregister(struct device *dev,
+			     struct counter_device *const counter)
+{
+	int rc;
+
+	rc = devres_release(dev, devm_counter_unreg, devm_counter_match,
+			    counter);
+	WARN_ON(rc);
+}
+EXPORT_SYMBOL_GPL(devm_counter_unregister);
+
+static int __init counter_init(void)
+{
+	return bus_register(&counter_bus_type);
+}
+
+static void __exit counter_exit(void)
+{
+	bus_unregister(&counter_bus_type);
+}
+
+subsys_initcall(counter_init);
+module_exit(counter_exit);
+
+MODULE_AUTHOR("William Breathitt Gray <vilhelm.gray@gmail.com>");
+MODULE_DESCRIPTION("Generic Counter interface");
+MODULE_LICENSE("GPL v2");