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From:   Bartosz Golaszewski <brgl@bgdev.pl>
To:     Linus Walleij <linus.walleij@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kent Gibson <warthog618@gmail.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Subject: [RFC PATCH] gpio: consumer: new virtual driver
Date:   Wed,  2 Aug 2023 17:28:08 +0200
Message-Id: <20230802152808.33037-1-brgl@bgdev.pl>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

The GPIO subsystem has a serious problem with undefined behavior and
use-after-free bugs on hot-unplug of GPIO chips. This can be considered a
corner-case by some as most GPIO controllers are enabled early in the
boot process and live until the system goes down but most GPIO drivers
do allow unbind over sysfs, many are loadable modules that can be (force)
unloaded and there are also GPIO devices that can be dynamically detached,
for instance CP2112 which is a USB GPIO expender.

Bugs can be triggered both from user-space as well as by in-kernel users.
We have the means of testing it from user-space via the character device
but the issues manifest themselves differently in the kernel.

This is a proposition of adding a new virtual driver - a configurable
GPIO consumer that can be configured over configfs (similarly to
gpio-sim).

The configfs interface allows users to create dynamic GPIO lookup tables
that are registered with the GPIO subsystem. Every config group
represents a consumer device. Every sub-group represents a single GPIO
lookup. The device can work in three modes: just keeping the line
active, toggling it every second or requesting its interrupt and
reporting edges. Every lookup allows to specify the key, offset and
flags as per the lookup struct defined in linux/gpio/machine.h.

The module together with gpio-sim allows to easily trigger kernel
hot-unplug errors. A simple use-case is to create a simulated chip,
setup the consumer to lookup one of its lines in 'monitor' mode, unbind
the simulator, unbind the consumer and observe the fireworks in dmesg.

This driver is aimed as a helper in tackling the hot-unplug problem in
GPIO as well as basis for future regression testing once the fixes are
upstream.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/Kconfig         |    7 +
 drivers/gpio/Makefile        |    1 +
 drivers/gpio/gpio-consumer.c | 1004 ++++++++++++++++++++++++++++++++++
 3 files changed, 1012 insertions(+)
 create mode 100644 drivers/gpio/gpio-consumer.c

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index e382dfebad7c..ddae605341fd 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1796,6 +1796,13 @@ config GPIO_SIM
 	  This enables the GPIO simulator - a configfs-based GPIO testing
 	  driver.
 
+config GPIO_CONSUMER
+	tristate "GPIO Consumer Testing Module"
+	select CONFIGFS_FS
+	help
+	  This enables the configurable, configfs-based virtual GPIO consumer
+	  testing driver.
+
 endmenu
 
 endif
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index c3ac51d47aa9..268e8f65f3c8 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_GPIO_BT8XX)		+= gpio-bt8xx.o
 obj-$(CONFIG_GPIO_CADENCE)		+= gpio-cadence.o
 obj-$(CONFIG_GPIO_CLPS711X)		+= gpio-clps711x.o
 obj-$(CONFIG_GPIO_SNPS_CREG)		+= gpio-creg-snps.o
+obj-$(CONFIG_GPIO_CONSUMER)		+= gpio-consumer.o
 obj-$(CONFIG_GPIO_CRYSTAL_COVE)		+= gpio-crystalcove.o
 obj-$(CONFIG_GPIO_CS5535)		+= gpio-cs5535.o
 obj-$(CONFIG_GPIO_DA9052)		+= gpio-da9052.o
diff --git a/drivers/gpio/gpio-consumer.c b/drivers/gpio/gpio-consumer.c
new file mode 100644
index 000000000000..fc6657e1af91
--- /dev/null
+++ b/drivers/gpio/gpio-consumer.c
@@ -0,0 +1,1004 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Configurable virtual GPIO consumer module.
+ *
+ * Copyright (C) 2023 Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/completion.h>
+#include <linux/configfs.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/machine.h>
+#include <linux/idr.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/printk.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/timer.h>
+
+#include "gpiolib.h"
+
+#define GPIO_CONSUMER_MAX_PROPS 3
+
+enum gpio_consumer_function {
+	GPIO_CONSUMER_FUNCTION_ACTIVE = 0,
+	GPIO_CONSUMER_FUNCTION_TOGGLE,
+	GPIO_CONSUMER_FUNCTION_MONITOR,
+	__GPIO_CONSUMER_FUNCTION_LAST,
+};
+
+static const char *const gpio_consumer_function_strings[] = {
+	[GPIO_CONSUMER_FUNCTION_ACTIVE] = "active",
+	[GPIO_CONSUMER_FUNCTION_TOGGLE] = "toggle",
+	[GPIO_CONSUMER_FUNCTION_MONITOR] = "monitor",
+	NULL
+};
+
+struct gpio_consumer_irq_data {
+	struct device *dev;
+	struct gpio_desc *desc;
+};
+
+struct gpio_consumer_timer_data {
+	struct timer_list timer;
+	struct gpio_desc *desc;
+	int val;
+};
+
+static struct gpio_consumer_timer_data *to_timer_data(struct timer_list *timer)
+{
+	return container_of(timer, struct gpio_consumer_timer_data, timer);
+}
+
+static DEFINE_IDA(gpio_consumer_ida);
+
+static irqreturn_t gpio_consumer_on_irq(int irq, void *data)
+{
+	struct gpio_consumer_irq_data *irq_data = data;
+	struct gpio_desc *desc = irq_data->desc;
+	struct gpio_device *gdev = desc->gdev;
+	struct device *dev = irq_data->dev;
+	int val;
+
+	val = gpiod_get_value_cansleep(desc);
+	if (val < 0) {
+		dev_err(dev, "failed to read GPIO value: %d\n", val);
+		return IRQ_HANDLED;
+	}
+
+	dev_info(dev, "interrupt triggered on line %u of %s, new value: %d\n",
+		 gpio_chip_hwgpio(desc), dev_name(&gdev->dev), val);
+
+	return IRQ_HANDLED;
+}
+
+static void gpio_consumer_on_timer(struct timer_list *timer)
+{
+	struct gpio_consumer_timer_data *timer_data = to_timer_data(timer);
+
+	timer_data->val = timer_data->val == 0 ? 1 : 0;
+	gpiod_set_value_cansleep(timer_data->desc, timer_data->val);
+	mod_timer(&timer_data->timer, jiffies + msecs_to_jiffies(1000));
+}
+
+static void gpio_consumer_del_timer(void *data)
+{
+	struct timer_list *timer = data;
+
+	del_timer(timer);
+}
+
+static int gpio_consumer_probe(struct platform_device *pdev)
+{
+	struct gpio_consumer_timer_data *timer_data;
+	struct gpio_consumer_irq_data *irq_data;
+	enum gpio_consumer_function function;
+	const char *function_prop, **lines;
+	struct device *dev = &pdev->dev;
+	struct gpio_desc *desc;
+	enum gpiod_flags flags;
+	int ret, num_lines, i;
+
+	ret = device_property_read_string(dev, "gpio-virtual-consumer,function",
+					  &function_prop);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to read the consumer GPIO function\n");
+
+	ret = match_string(gpio_consumer_function_strings, -1, function_prop);
+	if (ret < 0)
+		return dev_err_probe(dev, -EINVAL,
+				     "Invalid consumer function: '%s'\n",
+				     function_prop);
+
+	function = ret;
+	num_lines = device_property_string_array_count(dev,
+					"gpio-virtual-consumer,lines");
+	if (num_lines < 0)
+		return dev_err_probe(dev, num_lines,
+				     "List of GPIO lines to request not found\n");
+
+	lines = devm_kcalloc(dev, num_lines, sizeof(*lines), GFP_KERNEL);
+	if (!lines)
+		return -ENOMEM;
+
+	ret = device_property_read_string_array(dev,
+						"gpio-virtual-consumer,lines",
+						lines, num_lines);
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "Failed to read GPIO line names\n");
+
+	flags = function == GPIO_CONSUMER_FUNCTION_MONITOR ?
+					GPIOD_IN : GPIOD_OUT_HIGH;
+	for (i = 0; i < num_lines; i++) {
+		desc = devm_gpiod_get(dev, lines[i], flags);
+		if (IS_ERR(desc))
+			return dev_err_probe(dev, PTR_ERR(desc),
+					     "Failed to get GPIO '%s'\n",
+					     lines[i]);
+
+		if (function == GPIO_CONSUMER_FUNCTION_MONITOR) {
+			irq_data = devm_kzalloc(dev, sizeof(*irq_data),
+						GFP_KERNEL);
+			if (!irq_data)
+				return -ENOMEM;
+
+			irq_data->dev = dev;
+			irq_data->desc = desc;
+
+			ret = devm_request_threaded_irq(dev, gpiod_to_irq(desc),
+							NULL,
+							gpio_consumer_on_irq,
+							IRQF_TRIGGER_FALLING |
+							IRQF_TRIGGER_RISING |
+							IRQF_ONESHOT,
+							lines[i], irq_data);
+			if (ret)
+				return dev_err_probe(dev, ret,
+						"Failed to request GPIO line interrupt\n");
+		} else if (function == GPIO_CONSUMER_FUNCTION_TOGGLE) {
+			timer_data = devm_kzalloc(dev, sizeof(*timer_data),
+						  GFP_KERNEL);
+			if (!timer_data)
+				return -ENOMEM;
+
+			timer_data->desc = desc;
+			timer_data->val = 1;
+
+			timer_setup(&timer_data->timer,
+				    gpio_consumer_on_timer, 0);
+			mod_timer(&timer_data->timer,
+				  jiffies + msecs_to_jiffies(1000));
+
+			ret = devm_add_action_or_reset(dev,
+						       gpio_consumer_del_timer,
+						       &timer_data->timer);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+static const struct of_device_id gpio_consumer_of_match[] = {
+	{ .compatible = "gpio-virtual-consumer" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, gpio_consumer_of_match);
+
+static struct platform_driver gpio_consumer_driver = {
+	.driver = {
+		.name = "gpio-virtual-consumer",
+		.of_match_table = gpio_consumer_of_match,
+	},
+	.probe = gpio_consumer_probe,
+};
+
+struct gpio_consumer_device {
+	struct config_group group;
+
+	struct platform_device *pdev;
+	int id;
+	struct mutex lock;
+
+	struct notifier_block bus_notifier;
+	struct completion probe_completion;
+	bool driver_bound;
+
+	struct gpiod_lookup_table *lookup_table;
+	enum gpio_consumer_function function;
+
+	struct list_head lookup_list;
+};
+
+static int gpio_consumer_bus_notifier_call(struct notifier_block *nb,
+					   unsigned long action, void *data)
+{
+	struct gpio_consumer_device *consumer;
+	struct device *dev = data;
+	char devname[32];
+
+	consumer = container_of(nb, struct gpio_consumer_device, bus_notifier);
+	snprintf(devname, sizeof(devname), "gpio-virtual-consumer.%d",
+		 consumer->id);
+
+	if (strcmp(dev_name(dev), devname) == 0) {
+		switch (action) {
+		case BUS_NOTIFY_BOUND_DRIVER:
+			consumer->driver_bound = true;
+			break;
+		case BUS_NOTIFY_DRIVER_NOT_BOUND:
+			consumer->driver_bound = false;
+			break;
+		default:
+			return NOTIFY_DONE;
+		}
+
+		complete(&consumer->probe_completion);
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct gpio_consumer_device *
+to_gpio_consumer_device(struct config_item *item)
+{
+	struct config_group *group = to_config_group(item);
+
+	return container_of(group, struct gpio_consumer_device, group);
+}
+
+static bool
+gpio_consumer_device_is_live_unlocked(struct gpio_consumer_device *dev)
+{
+	return !!dev->pdev;
+}
+
+struct gpio_consumer_lookup {
+	struct config_group group;
+
+	struct gpio_consumer_device *parent;
+	struct list_head siblings;
+
+	char *con_id;
+	char *key;
+	/* Can be negative to indicate lookup by name. */
+	int offset;
+
+	enum gpio_lookup_flags flags;
+};
+
+static struct gpio_consumer_lookup *
+to_gpio_consumer_lookup(struct config_item *item)
+{
+	struct config_group *group = to_config_group(item);
+
+	return container_of(group, struct gpio_consumer_lookup, group);
+}
+
+static ssize_t
+gpio_consumer_lookup_config_key_show(struct config_item *item, char *page)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	int ret;
+
+	mutex_lock(&dev->lock);
+	ret = sprintf(page, "%s\n", lookup->key);
+	mutex_unlock(&dev->lock);
+
+	return ret;
+}
+
+static ssize_t
+gpio_consumer_lookup_config_key_store(struct config_item *item,
+				      const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	char *key, *stripped;
+
+	key = kstrndup(page, count, GFP_KERNEL);
+	if (!key)
+		return -ENOMEM;
+
+	stripped = strstrip(key);
+	memmove(key, stripped, strlen(stripped) + 1);
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		kfree(key);
+		return -EBUSY;
+	}
+
+	kfree(lookup->key);
+	lookup->key = key;
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, key);
+
+static ssize_t
+gpio_consumer_lookup_config_offset_show(struct config_item *item, char *page)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	unsigned int offset;
+
+	mutex_lock(&dev->lock);
+	offset = lookup->offset;
+	mutex_unlock(&dev->lock);
+
+	return sprintf(page, "%d\n", offset);
+}
+
+static ssize_t
+gpio_consumer_lookup_config_offset_store(struct config_item *item,
+					 const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	int offset, ret;
+
+	ret = kstrtoint(page, 0, &offset);
+	if (ret)
+		return ret;
+
+	/* Use -1 to indicate lookup by name. */
+	if (offset > (U16_MAX - 1))
+		return -EINVAL;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	lookup->offset = offset;
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, offset);
+
+static enum gpio_lookup_flags
+gpio_consumer_lookup_get_flags(struct config_item *item)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	enum gpio_lookup_flags flags;
+
+	mutex_lock(&dev->lock);
+	flags = lookup->flags;
+	mutex_unlock(&dev->lock);
+
+	return flags;
+}
+
+static ssize_t
+gpio_consumer_lookup_config_drive_show(struct config_item *item, char *page)
+{
+	enum gpio_lookup_flags flags;
+	const char *repr;
+
+	flags = gpio_consumer_lookup_get_flags(item);
+
+	if (flags & GPIO_OPEN_DRAIN)
+		repr = "open-drain";
+	else if (flags & GPIO_OPEN_SOURCE)
+		repr = "open-source";
+	else
+		repr = "push-pull";
+
+	return sprintf(page, "%s\n", repr);
+}
+
+static ssize_t
+gpio_consumer_lookup_config_drive_store(struct config_item *item,
+					const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	if (sysfs_streq(page, "push-pull")) {
+		lookup->flags &= ~(GPIO_OPEN_DRAIN | GPIO_OPEN_SOURCE);
+	} else if (sysfs_streq(page, "open-drain")) {
+		lookup->flags &= ~GPIO_OPEN_SOURCE;
+		lookup->flags |= GPIO_OPEN_DRAIN;
+	} else if (sysfs_streq(page, "open-source")) {
+		lookup->flags &= ~GPIO_OPEN_DRAIN;
+		lookup->flags |= GPIO_OPEN_SOURCE;
+	} else {
+		count = -EINVAL;
+	}
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, drive);
+
+static ssize_t
+gpio_consumer_lookup_config_pull_show(struct config_item *item, char *page)
+{
+	enum gpio_lookup_flags flags;
+	const char *repr;
+
+	flags = gpio_consumer_lookup_get_flags(item);
+
+	if (flags & GPIO_PULL_UP)
+		repr = "pull-up";
+	else if (flags & GPIO_PULL_DOWN)
+		repr = "pull-down";
+	else if (flags & GPIO_PULL_DISABLE)
+		repr = "pull-disabled";
+	else
+		repr = "as-is";
+
+	return sprintf(page, "%s\n", repr);
+}
+
+static ssize_t
+gpio_consumer_lookup_config_pull_store(struct config_item *item,
+				       const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	if (sysfs_streq(page, "pull-up")) {
+		lookup->flags &= ~(GPIO_PULL_DOWN | GPIO_PULL_DISABLE);
+		lookup->flags |= GPIO_PULL_UP;
+	} else if (sysfs_streq(page, "pull-down")) {
+		lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DISABLE);
+		lookup->flags |= GPIO_PULL_DOWN;
+	} else if (sysfs_streq(page, "pull-disabled")) {
+		lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DOWN);
+		lookup->flags |= GPIO_PULL_DISABLE;
+	} else if (sysfs_streq(page, "as-is")) {
+		lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DOWN |
+				   GPIO_PULL_DISABLE);
+	} else {
+		count = -EINVAL;
+	}
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, pull);
+
+static ssize_t
+gpio_consumer_lookup_config_active_low_show(struct config_item *item,
+					    char *page)
+{
+	enum gpio_lookup_flags flags;
+
+	flags = gpio_consumer_lookup_get_flags(item);
+
+	return sprintf(page, "%s\n", flags & GPIO_ACTIVE_LOW ? "1" : "0");
+}
+
+static ssize_t
+gpio_consumer_lookup_config_active_low_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	bool active_low;
+	int ret;
+
+	ret = kstrtobool(page, &active_low);
+	if (ret)
+		return ret;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	if (active_low)
+		lookup->flags |= GPIO_ACTIVE_LOW;
+	else
+		lookup->flags &= ~GPIO_ACTIVE_LOW;
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, active_low);
+
+static ssize_t
+gpio_consumer_lookup_config_transitory_show(struct config_item *item,
+					    char *page)
+{
+	enum gpio_lookup_flags flags;
+
+	flags = gpio_consumer_lookup_get_flags(item);
+
+	return sprintf(page, "%s\n", flags & GPIO_TRANSITORY ? "1" : "0");
+}
+
+static ssize_t
+gpio_consumer_lookup_config_transitory_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+	bool transitory;
+	int ret;
+
+	ret = kstrtobool(page, &transitory);
+	if (ret)
+		return ret;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	if (transitory)
+		lookup->flags |= GPIO_TRANSITORY;
+	else
+		lookup->flags &= ~GPIO_TRANSITORY;
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_lookup_config_, transitory);
+
+static struct configfs_attribute *gpio_consumer_lookup_config_attrs[] = {
+	&gpio_consumer_lookup_config_attr_key,
+	&gpio_consumer_lookup_config_attr_offset,
+	&gpio_consumer_lookup_config_attr_drive,
+	&gpio_consumer_lookup_config_attr_pull,
+	&gpio_consumer_lookup_config_attr_active_low,
+	&gpio_consumer_lookup_config_attr_transitory,
+	NULL
+};
+
+static ssize_t gpio_consumer_device_config_live_show(struct config_item *item,
+						     char *page)
+{
+	struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
+	bool live;
+
+	mutex_lock(&dev->lock);
+	live = gpio_consumer_device_is_live_unlocked(dev);
+	mutex_unlock(&dev->lock);
+
+	return sprintf(page, "%c\n", live ? '1' : '0');
+}
+
+static int
+gpio_consumer_make_lookup_table_unlocked(struct gpio_consumer_device *dev)
+{
+	struct gpio_consumer_lookup *lookup;
+	struct gpiod_lookup_table *table;
+	struct gpiod_lookup *curr;
+	size_t num_entries;
+	unsigned int i = 0;
+
+	num_entries = list_count_nodes(&dev->lookup_list);
+	table = kzalloc(sizeof(*table) + num_entries * sizeof(*table->table),
+			GFP_KERNEL);
+	if (!table)
+		return -ENOMEM;
+
+	table->dev_id = kasprintf(GFP_KERNEL, "gpio-virtual-consumer.%d",
+				  dev->id);
+	if (!table->dev_id) {
+		kfree(table);
+		return -ENOMEM;
+	}
+
+	list_for_each_entry(lookup, &dev->lookup_list, siblings) {
+		curr = &table->table[i];
+
+		curr->key = lookup->key;
+		curr->chip_hwnum = lookup->offset < 0 ?
+					U16_MAX : lookup->offset;
+		curr->con_id = lookup->con_id;
+		curr->flags = lookup->flags;
+	}
+
+	gpiod_add_lookup_table(table);
+	dev->lookup_table = table;
+
+	return 0;
+}
+
+static struct fwnode_handle *
+gpio_consumer_make_device_swnode(struct gpio_consumer_device *dev)
+{
+	struct property_entry properties[GPIO_CONSUMER_MAX_PROPS];
+	struct gpio_consumer_lookup *lookup;
+	struct fwnode_handle *swnode;
+	int prop_idx = 0, i = 0;
+	size_t num_lookups;
+	char **lines;
+
+	memset(properties, 0, sizeof(properties));
+
+	properties[prop_idx++] = PROPERTY_ENTRY_STRING(
+			"gpio-virtual-consumer,function",
+			gpio_consumer_function_strings[dev->function]);
+
+	num_lookups = list_count_nodes(&dev->lookup_list);
+	lines = kcalloc(num_lookups + 1, sizeof(*lines), GFP_KERNEL);
+	if (!lines)
+		return ERR_PTR(-ENOMEM);
+
+	list_for_each_entry(lookup, &dev->lookup_list, siblings)
+		lines[i++] = lookup->con_id;
+
+	properties[prop_idx++] = PROPERTY_ENTRY_STRING_ARRAY_LEN(
+		"gpio-virtual-consumer,lines", lines, num_lookups);
+
+	swnode = fwnode_create_software_node(properties, NULL);
+	kfree(lines);
+	return swnode;
+}
+
+static int
+gpio_consumer_device_activate_unlocked(struct gpio_consumer_device *dev)
+{
+	struct platform_device_info pdevinfo;
+	struct fwnode_handle *swnode;
+	struct platform_device *pdev;
+	int ret;
+
+	if (list_empty(&dev->lookup_list))
+		return -ENODATA;
+
+	swnode = gpio_consumer_make_device_swnode(dev);
+	if (IS_ERR(swnode))
+		return PTR_ERR(swnode);
+
+	memset(&pdevinfo, 0, sizeof(pdevinfo));
+	pdevinfo.name = "gpio-virtual-consumer";
+	pdevinfo.id = dev->id;
+	pdevinfo.fwnode = swnode;
+
+	ret = gpio_consumer_make_lookup_table_unlocked(dev);
+	if (ret) {
+		fwnode_remove_software_node(swnode);
+		return ret;
+	}
+
+	reinit_completion(&dev->probe_completion);
+	dev->driver_bound = false;
+	bus_register_notifier(&platform_bus_type, &dev->bus_notifier);
+
+	pdev = platform_device_register_full(&pdevinfo);
+	if (IS_ERR(pdev)) {
+		bus_unregister_notifier(&platform_bus_type, &dev->bus_notifier);
+		fwnode_remove_software_node(swnode);
+		return PTR_ERR(pdev);
+	}
+
+	wait_for_completion(&dev->probe_completion);
+	bus_unregister_notifier(&platform_bus_type, &dev->bus_notifier);
+
+	if (!dev->driver_bound) {
+		platform_device_unregister(pdev);
+		fwnode_remove_software_node(swnode);
+		return -ENXIO;
+	}
+
+	dev->pdev = pdev;
+
+	return 0;
+}
+
+static void
+gpio_consumer_device_deactivate_unlocked(struct gpio_consumer_device *dev)
+{
+	struct fwnode_handle *swnode;
+
+	swnode = dev_fwnode(&dev->pdev->dev);
+	platform_device_unregister(dev->pdev);
+	fwnode_remove_software_node(swnode);
+	dev->pdev = NULL;
+	kfree(dev->lookup_table);
+}
+
+static ssize_t
+gpio_consumer_device_config_live_store(struct config_item *item,
+				       const char *page, size_t count)
+{
+	struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
+	bool live;
+	int ret;
+
+	ret = kstrtobool(page, &live);
+	if (ret)
+		return ret;
+
+	mutex_lock(&dev->lock);
+
+	if ((!live && !gpio_consumer_device_is_live_unlocked(dev)) ||
+	    (live && gpio_consumer_device_is_live_unlocked(dev)))
+		ret = -EPERM;
+	else if (live)
+		ret = gpio_consumer_device_activate_unlocked(dev);
+	else
+		gpio_consumer_device_deactivate_unlocked(dev);
+
+	mutex_unlock(&dev->lock);
+
+	return ret ?: count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_device_config_, live);
+
+static ssize_t
+gpio_consumer_device_config_function_show(struct config_item *item, char *page)
+{
+	struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
+	enum gpio_consumer_function function;
+	const char *repr;
+
+	mutex_lock(&dev->lock);
+	function = dev->function;
+	mutex_unlock(&dev->lock);
+
+	repr = gpio_consumer_function_strings[function];
+
+	return sprintf(page, "%s\n", repr);
+}
+
+static ssize_t
+gpio_consumer_device_config_function_store(struct config_item *item,
+					   const char *page, size_t count)
+{
+	struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
+	int ret;
+
+	ret = sysfs_match_string(gpio_consumer_function_strings, page);
+	if (ret < 0)
+		return -EINVAL;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return -EBUSY;
+	}
+
+	dev->function = ret;
+
+	mutex_unlock(&dev->lock);
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_consumer_device_config_, function);
+
+static struct configfs_attribute *gpio_consumer_device_config_attrs[] = {
+	&gpio_consumer_device_config_attr_live,
+	&gpio_consumer_device_config_attr_function,
+	NULL
+};
+
+static void gpio_consumer_lookup_config_group_release(struct config_item *item)
+{
+	struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
+	struct gpio_consumer_device *dev = lookup->parent;
+
+	mutex_lock(&dev->lock);
+	list_del(&lookup->siblings);
+	mutex_unlock(&dev->lock);
+
+	kfree(lookup->con_id);
+	kfree(lookup->key);
+	kfree(lookup);
+}
+
+static struct configfs_item_operations gpio_consumer_lookup_config_item_ops = {
+	.release	= gpio_consumer_lookup_config_group_release,
+};
+
+static const struct config_item_type gpio_consumer_lookup_config_group_type = {
+	.ct_item_ops	= &gpio_consumer_lookup_config_item_ops,
+	.ct_attrs	= gpio_consumer_lookup_config_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_group *
+gpio_consumer_device_make_lookup_group(struct config_group *group,
+				       const char *name)
+{
+	struct gpio_consumer_device *dev =
+			to_gpio_consumer_device(&group->cg_item);
+	struct gpio_consumer_lookup *lookup;
+
+	mutex_lock(&dev->lock);
+
+	if (gpio_consumer_device_is_live_unlocked(dev)) {
+		mutex_unlock(&dev->lock);
+		return ERR_PTR(-EBUSY);
+	}
+
+	lookup = kzalloc(sizeof(*lookup), GFP_KERNEL);
+	if (!lookup) {
+		mutex_unlock(&dev->lock);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	lookup->con_id = kstrdup(name, GFP_KERNEL);
+	if (!lookup->con_id) {
+		mutex_unlock(&dev->lock);
+		kfree(lookup);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	config_group_init_type_name(&lookup->group, name,
+				    &gpio_consumer_lookup_config_group_type);
+	lookup->flags = GPIO_LOOKUP_FLAGS_DEFAULT;
+	lookup->parent = dev;
+	list_add_tail(&lookup->siblings, &dev->lookup_list);
+
+	mutex_unlock(&dev->lock);
+
+	return &lookup->group;
+}
+
+static void gpio_consumer_device_config_group_release(struct config_item *item)
+{
+	struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
+
+	mutex_lock(&dev->lock);
+	if (gpio_consumer_device_is_live_unlocked(dev))
+		gpio_consumer_device_deactivate_unlocked(dev);
+	mutex_unlock(&dev->lock);
+
+	mutex_destroy(&dev->lock);
+	ida_free(&gpio_consumer_ida, dev->id);
+	kfree(dev);
+}
+
+static struct configfs_item_operations gpio_consumer_device_config_item_ops = {
+	.release	= gpio_consumer_device_config_group_release,
+};
+
+static struct configfs_group_operations gpio_consumer_device_config_group_ops = {
+	.make_group	= gpio_consumer_device_make_lookup_group,
+};
+
+static const struct config_item_type gpio_consumer_device_config_group_type = {
+	.ct_group_ops	= &gpio_consumer_device_config_group_ops,
+	.ct_item_ops	= &gpio_consumer_device_config_item_ops,
+	.ct_attrs	= gpio_consumer_device_config_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_group *
+gpio_consumer_config_make_device_group(struct config_group *group,
+				       const char *name)
+{
+	struct gpio_consumer_device *dev;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	dev->id = ida_alloc(&gpio_consumer_ida, GFP_KERNEL);
+	if (dev->id < 0) {
+		kfree(dev);
+		return ERR_PTR(dev->id);
+	}
+
+	config_group_init_type_name(&dev->group, name,
+				    &gpio_consumer_device_config_group_type);
+	mutex_init(&dev->lock);
+	INIT_LIST_HEAD(&dev->lookup_list);
+	dev->bus_notifier.notifier_call = gpio_consumer_bus_notifier_call;
+	dev->function = GPIO_CONSUMER_FUNCTION_ACTIVE;
+	init_completion(&dev->probe_completion);
+
+	return &dev->group;
+}
+
+static struct configfs_group_operations gpio_consumer_config_group_ops = {
+	.make_group	= gpio_consumer_config_make_device_group,
+};
+
+static const struct config_item_type gpio_consumer_config_type = {
+	.ct_group_ops	= &gpio_consumer_config_group_ops,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct configfs_subsystem gpio_consumer_config_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf	= "gpio-consumer",
+			.ci_type	= &gpio_consumer_config_type,
+		},
+	},
+};
+
+static int __init gpio_consumer_init(void)
+{
+	int ret;
+
+	ret = platform_driver_register(&gpio_consumer_driver);
+	if (ret) {
+		pr_err("Failed to register the gpio-consumer platform driver: %d\n",
+		       ret);
+		return ret;
+	}
+
+	config_group_init(&gpio_consumer_config_subsys.su_group);
+	mutex_init(&gpio_consumer_config_subsys.su_mutex);
+	ret = configfs_register_subsystem(&gpio_consumer_config_subsys);
+	if (ret) {
+		pr_err("Failed to register the '%s' configfs subsystem: %d\n",
+		       gpio_consumer_config_subsys.su_group.cg_item.ci_namebuf,
+		       ret);
+		mutex_destroy(&gpio_consumer_config_subsys.su_mutex);
+		platform_driver_unregister(&gpio_consumer_driver);
+		return ret;
+	}
+
+	return 0;
+}
+module_init(gpio_consumer_init);
+
+static void __exit gpio_consumer_exit(void)
+{
+	configfs_unregister_subsystem(&gpio_consumer_config_subsys);
+	mutex_destroy(&gpio_consumer_config_subsys.su_mutex);
+	platform_driver_unregister(&gpio_consumer_driver);
+}
+module_exit(gpio_consumer_exit);
+
+MODULE_AUTHOR("Bartosz Golaszewski <bartosz.golaszewski@linaro.org>");
+MODULE_DESCRIPTION("Virtual GPIO consumer module");
+MODULE_LICENSE("GPL");
-- 
2.39.2