[v3,08/13] gpio: aggregator: introduce basic configfs interface

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 8b9ffe17426e..591244e6cd4e 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1871,6 +1871,7 @@  menu "Virtual GPIO drivers"
 
 config GPIO_AGGREGATOR
 	tristate "GPIO Aggregator"
+	select CONFIGFS_FS
 	select GPIO_PSEUDO
 	help
 	  Say yes here to enable the GPIO Aggregator, which provides a way to
diff --git a/drivers/gpio/gpio-aggregator.c b/drivers/gpio/gpio-aggregator.c
index 6252a686f805..ec102453817b 100644
--- a/drivers/gpio/gpio-aggregator.c
+++ b/drivers/gpio/gpio-aggregator.c
@@ -9,10 +9,13 @@ 
 
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
+#include <linux/configfs.h>
 #include <linux/ctype.h>
 #include <linux/delay.h>
 #include <linux/idr.h>
 #include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -37,11 +40,35 @@ 
 
 struct gpio_aggregator {
 	struct pseudo_gpio_common common;
+	struct config_group group;
 	struct gpiod_lookup_table *lookups;
+	struct mutex lock;
 	int id;
+
+	/* List of gpio_aggregator_line. Always added in order */
+	struct list_head list_head;
+
+	/* used by legacy sysfs interface only */
+	bool init_via_sysfs;
 	char args[];
 };
 
+struct gpio_aggregator_line {
+	struct config_group group;
+	struct gpio_aggregator *parent;
+	struct list_head entry;
+
+	/* Line index within the aggregator device */
+	unsigned int idx;
+
+	/* GPIO chip label or line name */
+	const char *key;
+	/* Can be negative to indicate lookup by line name */
+	int offset;
+
+	enum gpio_lookup_flags flags;
+};
+
 static DEFINE_MUTEX(gpio_aggregator_lock);	/* protects idr */
 static DEFINE_IDR(gpio_aggregator_idr);
 
@@ -61,6 +88,8 @@  static int aggr_alloc(struct gpio_aggregator **aggr, size_t arg_size)
 		return ret;
 
 	new->id = ret;
+	INIT_LIST_HEAD(&new->list_head);
+	mutex_init(&new->lock);
 	*aggr = no_free_ptr(new);
 	return 0;
 }
@@ -70,6 +99,7 @@  static void aggr_free(struct gpio_aggregator *aggr)
 	mutex_lock(&gpio_aggregator_lock);
 	idr_remove(&gpio_aggregator_idr, aggr->id);
 	mutex_unlock(&gpio_aggregator_lock);
+	mutex_destroy(&aggr->lock);
 	kfree(aggr);
 }
 
@@ -92,6 +122,70 @@  static int aggr_add_gpio(struct gpio_aggregator *aggr, const char *key,
 	return 0;
 }
 
+static bool aggr_is_active(struct gpio_aggregator *aggr)
+{
+	lockdep_assert_held(&aggr->lock);
+
+	return aggr->common.pdev && platform_get_drvdata(aggr->common.pdev);
+}
+
+static size_t aggr_count_lines(struct gpio_aggregator *aggr)
+{
+	lockdep_assert_held(&aggr->lock);
+
+	return list_count_nodes(&aggr->list_head);
+}
+
+static struct gpio_aggregator_line *aggr_line_alloc(
+		struct gpio_aggregator *parent, unsigned int idx, char *key, int offset)
+{
+	struct gpio_aggregator_line *line;
+
+	line = kzalloc(sizeof(*line), GFP_KERNEL);
+	if (!line)
+		return ERR_PTR(-ENOMEM);
+
+	if (key) {
+		line->key = kstrdup(key, GFP_KERNEL);
+		if (!line->key) {
+			kfree(line);
+			return ERR_PTR(-ENOMEM);
+		}
+	}
+
+	line->flags = GPIO_LOOKUP_FLAGS_DEFAULT;
+	line->parent = parent;
+	line->idx = idx;
+	line->offset = offset;
+	INIT_LIST_HEAD(&line->entry);
+
+	return line;
+}
+
+static void aggr_line_add(struct gpio_aggregator *aggr,
+			  struct gpio_aggregator_line *line)
+{
+	struct gpio_aggregator_line *tmp;
+
+	lockdep_assert_held(&aggr->lock);
+
+	list_for_each_entry(tmp, &aggr->list_head, entry) {
+		if (tmp->idx > line->idx) {
+			list_add_tail(&line->entry, &tmp->entry);
+			return;
+		}
+	}
+	list_add_tail(&line->entry, &aggr->list_head);
+}
+
+static void aggr_line_del(struct gpio_aggregator *aggr,
+			  struct gpio_aggregator_line *line)
+{
+	lockdep_assert_held(&aggr->lock);
+
+	list_del(&line->entry);
+}
+
 
 /*
  *  GPIO Forwarder
@@ -416,6 +510,400 @@  static struct gpiochip_fwd *gpiochip_fwd_create(struct device *dev,
 }
 
 
+/*
+ * Configfs interface
+ */
+
+static struct gpio_aggregator *
+to_gpio_aggregator(struct config_item *item)
+{
+	struct config_group *group = to_config_group(item);
+
+	return container_of(group, struct gpio_aggregator, group);
+}
+
+static struct gpio_aggregator_line *
+to_gpio_aggregator_line(struct config_item *item)
+{
+	struct config_group *group = to_config_group(item);
+
+	return container_of(group, struct gpio_aggregator_line, group);
+}
+
+static int aggr_activate(struct gpio_aggregator *aggr)
+{
+	struct platform_device_info pdevinfo;
+	struct gpio_aggregator_line *line;
+	unsigned int n = 0;
+	int ret = 0;
+
+	if (aggr_count_lines(aggr) == 0)
+		return -EINVAL;
+
+	aggr->lookups = kzalloc(struct_size(aggr->lookups, table, 1),
+				GFP_KERNEL);
+	if (!aggr->lookups)
+		return -ENOMEM;
+
+	memset(&pdevinfo, 0, sizeof(pdevinfo));
+	pdevinfo.name = DRV_NAME;
+	pdevinfo.id = aggr->id;
+
+	/* The list is always sorted as new elements are inserted in order. */
+	list_for_each_entry(line, &aggr->list_head, entry) {
+		/*
+		 * - Either GPIO chip label or line name must be configured
+		 *   (i.e. line->key must be non-NULL)
+		 * - Line directories must be named with sequential numeric
+		 *   suffixes starting from 0. (i.e. ./line0, ./line1, ...)
+		 */
+		if (!line->key || line->idx != n) {
+			ret = -EINVAL;
+			goto err_remove_lookups;
+		}
+
+		if (line->offset < 0)
+			ret = aggr_add_gpio(aggr, line->key, U16_MAX, &n);
+		else
+			ret = aggr_add_gpio(aggr, line->key, line->offset, &n);
+		if (ret)
+			goto err_remove_lookups;
+	}
+
+	aggr->lookups->dev_id = kasprintf(GFP_KERNEL, "%s.%d", DRV_NAME, aggr->id);
+	if (!aggr->lookups->dev_id) {
+		ret = -ENOMEM;
+		goto err_remove_lookups;
+	}
+
+	gpiod_add_lookup_table(aggr->lookups);
+
+	ret = pseudo_gpio_register(&aggr->common, &pdevinfo);
+	if (ret)
+		goto err_remove_lookup_table;
+
+	return 0;
+
+err_remove_lookup_table:
+	kfree(aggr->lookups->dev_id);
+	gpiod_remove_lookup_table(aggr->lookups);
+err_remove_lookups:
+	kfree(aggr->lookups);
+
+	return ret;
+}
+
+static void aggr_deactivate(struct gpio_aggregator *aggr)
+{
+	pseudo_gpio_unregister(&aggr->common);
+	gpiod_remove_lookup_table(aggr->lookups);
+	kfree(aggr->lookups->dev_id);
+	kfree(aggr->lookups);
+}
+
+static void aggr_lockup_configfs(struct gpio_aggregator *aggr, bool lock)
+{
+	struct configfs_subsystem *subsys = aggr->group.cg_subsys;
+	struct gpio_aggregator_line *line;
+
+	/*
+	 * The device only needs to depend on leaf lines. This is
+	 * sufficient to lock up all the configfs entries that the
+	 * instantiated, alive device depends on.
+	 */
+	list_for_each_entry(line, &aggr->list_head, entry) {
+		if (lock)
+			configfs_depend_item_unlocked(
+					subsys, &line->group.cg_item);
+		else
+			configfs_undepend_item_unlocked(
+					&line->group.cg_item);
+	}
+}
+
+static ssize_t
+gpio_aggr_line_key_show(struct config_item *item, char *page)
+{
+	struct gpio_aggregator_line *line = to_gpio_aggregator_line(item);
+	struct gpio_aggregator *aggr = line->parent;
+
+	guard(mutex)(&aggr->lock);
+
+	return sysfs_emit(page, "%s\n", line->key ?: "");
+}
+
+static ssize_t
+gpio_aggr_line_key_store(struct config_item *item, const char *page,
+			 size_t count)
+{
+	struct gpio_aggregator_line *line = to_gpio_aggregator_line(item);
+	struct gpio_aggregator *aggr = line->parent;
+
+	char *key __free(kfree) = kstrndup(skip_spaces(page), count,
+					   GFP_KERNEL);
+	if (!key)
+		return -ENOMEM;
+
+	strim(key);
+
+	guard(mutex)(&aggr->lock);
+
+	if (aggr_is_active(aggr))
+		return -EBUSY;
+
+	kfree(line->key);
+	line->key = no_free_ptr(key);
+
+	return count;
+}
+CONFIGFS_ATTR(gpio_aggr_line_, key);
+
+static ssize_t
+gpio_aggr_line_offset_show(struct config_item *item, char *page)
+{
+	struct gpio_aggregator_line *line = to_gpio_aggregator_line(item);
+	struct gpio_aggregator *aggr = line->parent;
+	unsigned int offset;
+
+	scoped_guard(mutex, &aggr->lock)
+		offset = line->offset;
+
+	return sysfs_emit(page, "%d\n", offset);
+}
+
+static ssize_t
+gpio_aggr_line_offset_store(struct config_item *item, const char *page,
+			    size_t count)
+{
+	struct gpio_aggregator_line *line = to_gpio_aggregator_line(item);
+	struct gpio_aggregator *aggr = line->parent;
+	int offset, ret;
+
+	ret = kstrtoint(page, 0, &offset);
+	if (ret)
+		return ret;
+
+	/*
+	 * When offset == -1, 'key' represents a line name to lookup.
+	 * When 0 <= offset < 65535, 'key' represents the label of the chip with
+	 * the 'offset' value representing the line within that chip.
+	 *
+	 * GPIOLIB uses the U16_MAX value to indicate lookup by line name so
+	 * the greatest offset we can accept is (U16_MAX - 1).
+	 */
+	if (offset > (U16_MAX - 1) || offset < -1)
+		return -EINVAL;
+
+	guard(mutex)(&aggr->lock);
+
+	if (aggr_is_active(aggr))
+		return -EBUSY;
+
+	line->offset = offset;
+
+	return count;
+}
+CONFIGFS_ATTR(gpio_aggr_line_, offset);
+
+static struct configfs_attribute *gpio_aggr_line_attrs[] = {
+	&gpio_aggr_line_attr_key,
+	&gpio_aggr_line_attr_offset,
+	NULL
+};
+
+static ssize_t
+gpio_aggr_device_dev_name_show(struct config_item *item, char *page)
+{
+	struct gpio_aggregator *aggr = to_gpio_aggregator(item);
+	struct platform_device *pdev;
+
+	guard(mutex)(&aggr->lock);
+
+	pdev = aggr->common.pdev;
+	if (pdev)
+		return sysfs_emit(page, "%s\n", dev_name(&pdev->dev));
+
+	return sysfs_emit(page, "%s.%d\n", DRV_NAME, aggr->id);
+}
+CONFIGFS_ATTR_RO(gpio_aggr_device_, dev_name);
+
+static ssize_t
+gpio_aggr_device_live_show(struct config_item *item, char *page)
+{
+	struct gpio_aggregator *aggr = to_gpio_aggregator(item);
+	bool active;
+
+	scoped_guard(mutex, &aggr->lock)
+		active = aggr_is_active(aggr);
+
+	return sysfs_emit(page, "%c\n", active ? '1' : '0');
+}
+
+static ssize_t
+gpio_aggr_device_live_store(struct config_item *item, const char *page,
+			    size_t count)
+{
+	struct gpio_aggregator *aggr = to_gpio_aggregator(item);
+	int ret = 0;
+	bool live;
+
+	ret = kstrtobool(page, &live);
+	if (ret)
+		return ret;
+
+	if (!try_module_get(THIS_MODULE))
+		return -ENOENT;
+
+	if (live)
+		aggr_lockup_configfs(aggr, true);
+
+	scoped_guard(mutex, &aggr->lock) {
+		if (live == aggr_is_active(aggr))
+			ret = -EPERM;
+		else if (live)
+			ret = aggr_activate(aggr);
+		else
+			aggr_deactivate(aggr);
+	}
+
+	/*
+	 * Undepend is required only if device disablement (live == 0)
+	 * succeeds or if device enablement (live == 1) fails.
+	 */
+	if (live == !!ret)
+		aggr_lockup_configfs(aggr, false);
+
+	module_put(THIS_MODULE);
+
+	return ret ?: count;
+}
+CONFIGFS_ATTR(gpio_aggr_device_, live);
+
+static struct configfs_attribute *gpio_aggr_device_attrs[] = {
+	&gpio_aggr_device_attr_dev_name,
+	&gpio_aggr_device_attr_live,
+	NULL
+};
+
+static void
+gpio_aggr_line_release(struct config_item *item)
+{
+	struct gpio_aggregator_line *line = to_gpio_aggregator_line(item);
+	struct gpio_aggregator *aggr = line->parent;
+
+	guard(mutex)(&aggr->lock);
+
+	aggr_line_del(aggr, line);
+	kfree(line->key);
+	kfree(line);
+}
+
+static struct configfs_item_operations gpio_aggr_line_item_ops = {
+	.release	= gpio_aggr_line_release,
+};
+
+static const struct config_item_type gpio_aggr_line_type = {
+	.ct_item_ops	= &gpio_aggr_line_item_ops,
+	.ct_attrs	= gpio_aggr_line_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static void gpio_aggr_device_release(struct config_item *item)
+{
+	struct gpio_aggregator *aggr = to_gpio_aggregator(item);
+
+	guard(mutex)(&aggr->lock);
+
+	/*
+	 * If the aggregator is active, this code wouldn't be reached,
+	 * so calling aggr_deactivate() is always unnecessary.
+	 */
+	aggr_free(aggr);
+}
+
+static struct configfs_item_operations gpio_aggr_device_item_ops = {
+	.release	= gpio_aggr_device_release,
+};
+
+static struct config_group *
+gpio_aggr_device_make_group(struct config_group *group, const char *name)
+{
+	struct gpio_aggregator *aggr = to_gpio_aggregator(&group->cg_item);
+	struct gpio_aggregator_line *line;
+	unsigned int idx;
+	int ret, nchar;
+
+	ret = sscanf(name, "line%u%n", &idx, &nchar);
+	if (ret != 1 || nchar != strlen(name))
+		return ERR_PTR(-EINVAL);
+
+	guard(mutex)(&aggr->lock);
+
+	if (aggr_is_active(aggr))
+		return ERR_PTR(-EBUSY);
+
+	list_for_each_entry(line, &aggr->list_head, entry)
+		if (line->idx == idx)
+			return ERR_PTR(-EINVAL);
+
+	line = aggr_line_alloc(aggr, idx, NULL, -1);
+	if (!line)
+		return ERR_PTR(-ENOMEM);
+
+	config_group_init_type_name(&line->group, name, &gpio_aggr_line_type);
+
+	aggr_line_add(aggr, line);
+
+	return &line->group;
+}
+
+static struct configfs_group_operations gpio_aggr_device_group_ops = {
+	.make_group	= gpio_aggr_device_make_group,
+};
+
+static const struct config_item_type gpio_aggr_device_type = {
+	.ct_group_ops	= &gpio_aggr_device_group_ops,
+	.ct_item_ops	= &gpio_aggr_device_item_ops,
+	.ct_attrs	= gpio_aggr_device_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_group *
+gpio_aggr_make_group(struct config_group *group, const char *name)
+{
+	struct gpio_aggregator *aggr;
+	int ret;
+
+	/* arg space is unneeded */
+	ret = aggr_alloc(&aggr, 0);
+	if (ret)
+		return ERR_PTR(ret);
+
+	config_group_init_type_name(&aggr->group, name, &gpio_aggr_device_type);
+	pseudo_gpio_init(&aggr->common);
+
+	return &aggr->group;
+}
+
+static struct configfs_group_operations gpio_aggr_group_ops = {
+	.make_group	= gpio_aggr_make_group,
+};
+
+static const struct config_item_type gpio_aggr_type = {
+	.ct_group_ops	= &gpio_aggr_group_ops,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct configfs_subsystem gpio_aggr_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf	= DRV_NAME,
+			.ci_type	= &gpio_aggr_type,
+		},
+	},
+};
+
+
 /*
  * Sysfs interface
  */
@@ -487,6 +975,7 @@  static ssize_t new_device_store(struct device_driver *driver, const char *buf,
 
 	memcpy(aggr->args, buf, count + 1);
 
+	aggr->init_via_sysfs = true;
 	aggr->lookups = kzalloc(struct_size(aggr->lookups, table, 1),
 				GFP_KERNEL);
 	if (!aggr->lookups) {
@@ -533,10 +1022,7 @@  static DRIVER_ATTR_WO(new_device);
 
 static void gpio_aggregator_free(struct gpio_aggregator *aggr)
 {
-	platform_device_unregister(aggr->common.pdev);
-	gpiod_remove_lookup_table(aggr->lookups);
-	kfree(aggr->lookups->dev_id);
-	kfree(aggr->lookups);
+	aggr_deactivate(aggr);
 	kfree(aggr);
 }
 
@@ -558,12 +1044,19 @@  static ssize_t delete_device_store(struct device_driver *driver,
 		return -ENOENT;
 
 	mutex_lock(&gpio_aggregator_lock);
-	aggr = idr_remove(&gpio_aggregator_idr, id);
-	mutex_unlock(&gpio_aggregator_lock);
-	if (!aggr) {
+	aggr = idr_find(&gpio_aggregator_idr, id);
+	/*
+	 * For simplicity, devices created via configfs cannot be deleted
+	 * via sysfs.
+	 */
+	if (aggr && aggr->init_via_sysfs)
+		idr_remove(&gpio_aggregator_idr, id);
+	else {
+		mutex_unlock(&gpio_aggregator_lock);
 		module_put(THIS_MODULE);
 		return -ENOENT;
 	}
+	mutex_unlock(&gpio_aggregator_lock);
 
 	gpio_aggregator_free(aggr);
 	module_put(THIS_MODULE);
@@ -638,6 +1131,10 @@  static struct platform_driver gpio_aggregator_driver = {
 
 static int __exit gpio_aggregator_idr_remove(int id, void *p, void *data)
 {
+	/*
+	 * There should be no aggregator created via configfs, as their
+	 * presence would prevent module unloading.
+	 */
 	gpio_aggregator_free(p);
 	return 0;
 }
@@ -652,7 +1149,33 @@  static void __exit gpio_aggregator_remove_all(void)
 
 static int __init gpio_aggregator_init(void)
 {
-	return platform_driver_register(&gpio_aggregator_driver);
+	int ret = 0;
+
+	config_group_init(&gpio_aggr_subsys.su_group);
+	mutex_init(&gpio_aggr_subsys.su_mutex);
+	ret = configfs_register_subsystem(&gpio_aggr_subsys);
+	if (ret) {
+		pr_err("Failed to register the '%s' configfs subsystem: %d\n",
+		       gpio_aggr_subsys.su_group.cg_item.ci_namebuf, ret);
+		mutex_destroy(&gpio_aggr_subsys.su_mutex);
+		return ret;
+	}
+
+	/*
+	 * CAVEAT: This must occur after configfs registration. Otherwise,
+	 * a race condition could arise: driver attribute groups might be
+	 * exposed and accessed by users before configfs registration
+	 * completes. new_device_store() does not expect a partially
+	 * initialized configfs state.
+	 */
+	ret = platform_driver_register(&gpio_aggregator_driver);
+	if (ret) {
+		pr_err("Failed to register the platform driver: %d\n", ret);
+		mutex_destroy(&gpio_aggr_subsys.su_mutex);
+		configfs_unregister_subsystem(&gpio_aggr_subsys);
+	}
+
+	return ret;
 }
 module_init(gpio_aggregator_init);
 
@@ -660,6 +1183,7 @@  static void __exit gpio_aggregator_exit(void)
 {
 	gpio_aggregator_remove_all();
 	platform_driver_unregister(&gpio_aggregator_driver);
+	configfs_unregister_subsystem(&gpio_aggr_subsys);
 }
 module_exit(gpio_aggregator_exit);