Re: [PATCH v2 09/12] gpio: sim: new testing module

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Thu, Mar 04, 2021 at 11:24:49AM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> 
> Implement a new, modern GPIO testing module controlled by configfs
> attributes instead of module parameters. The goal of this driver is
> to provide a replacement for gpio-mockup that will be easily extensible
> with new features and doesn't require reloading the module to change
> the setup.

Shall we put a reference to this in the gpio-mockup documentation and mark the
latter deprecated?


> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> ---
>  Documentation/admin-guide/gpio/gpio-sim.rst |  72 ++
>  drivers/gpio/Kconfig                        |   8 +
>  drivers/gpio/Makefile                       |   1 +
>  drivers/gpio/gpio-sim.c                     | 878 ++++++++++++++++++++
>  4 files changed, 959 insertions(+)
>  create mode 100644 Documentation/admin-guide/gpio/gpio-sim.rst
>  create mode 100644 drivers/gpio/gpio-sim.c
> 
> diff --git a/Documentation/admin-guide/gpio/gpio-sim.rst b/Documentation/admin-guide/gpio/gpio-sim.rst
> new file mode 100644
> index 000000000000..08eac487e35e
> --- /dev/null
> +++ b/Documentation/admin-guide/gpio/gpio-sim.rst
> @@ -0,0 +1,72 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +Configfs GPIO Simulator
> +=======================
> +
> +The configfs GPIO Simulator (gpio-sim) provides a way to create simulated GPIO
> +chips for testing purposes. The lines exposed by these chips can be accessed
> +using the standard GPIO character device interface as well as manipulated
> +using sysfs attributes.
> +
> +Creating simulated chips
> +------------------------
> +
> +The gpio-sim module registers a configfs subsystem called 'gpio-sim'. It's a
> +subsystem with committable items which means two subdirectories are created in
> +the filesystem: pending and live. For more information on configfs and
> +committable items, please refer to Documentation/filesystems/configfs.rst.
> +
> +In order to instantiate a new simulated chip, the user needs to mkdir() a new
> +directory in pending/. Inside each new directory, there's a set of attributes
> +that can be used to configure the new chip. Once the configuration is complete,
> +the user needs to use rename() to move the chip to the live/ directory. This
> +creates and registers the new device.
> +
> +In order to destroy a simulated chip, it has to be moved back to pending first
> +and then removed using rmdir().
> +
> +Currently supported configuration attributes are:
> +
> +  num_lines - an unsigned integer value defining the number of GPIO lines to
> +              export
> +
> +  label - a string defining the label for the GPIO chip
> +
> +  line_names - a list of GPIO line names in the form of quoted strings
> +               separated by commas, e.g.: '"foo", "bar", "", "foobar"'. The
> +               number of strings doesn't have to be equal to the value set in
> +               the num_lines attribute. If it's lower than the number of lines,
> +               the remaining lines are unnamed. If it's larger, the superfluous
> +               lines are ignored. A name of the form: '""' means the line
> +               should be unnamed.
> +
> +Additionally two read-only attributes named 'chip_name' and 'dev_name' are
> +exposed in order to provide users with a mapping from configfs directories to
> +the actual devices created in the kernel. The former returns the name of the
> +GPIO device as assigned by gpiolib (i.e. "gpiochip0", "gpiochip1", etc.). The
> +latter returns the parent device name as defined by the gpio-sim driver (i.e.
> +"gpio-sim.0", "gpio-sim.1", etc.). This allows user-space to map the configfs
> +items both to the correct character device file as well as the associated entry
> +in sysfs.
> +
> +Simulated GPIO chips can also be defined in device-tree. The compatible string
> +must be: "gpio-simulator". Supported properties are:
> +
> +  "gpio-sim,label" - chip label
> +
> +  "gpio-sim,nr-gpios" - number of lines
> +
> +Other standard GPIO properties (like "gpio-line-names" and gpio-hog) are also
> +supported.
> +
> +Manipulating simulated lines
> +----------------------------
> +
> +Each simulated GPIO chip creates a sysfs attribute group under its device
> +directory called 'line-ctrl'. Inside each group, there's a separate attribute
> +for each GPIO line. The name of the attribute is of the form 'gpioX' where X
> +is the line's offset in the chip.
> +
> +Reading from a line attribute returns the current value. Writing to it (0 or 1)
> +changes the configuration of the simulated pull-up/pull-down resistor
> +(1 - pull-up, 0 - pull-down).
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index e3607ec4c2e8..b6b6150d0d04 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -1633,6 +1633,14 @@ config GPIO_MOCKUP
>  	  tools/testing/selftests/gpio/gpio-mockup.sh. Reference the usage in
>  	  it.
>  
> +config GPIO_SIM
> +	tristate "GPIO Simulator Module"
> +	select IRQ_SIM
> +	select CONFIGFS_FS
> +	help
> +	  This enables the GPIO simulator - a configfs-based GPIO testing
> +	  driver.
> +
>  endmenu
>  
>  endif
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index c58a90a3c3b1..d717aa85f8e1 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -130,6 +130,7 @@ obj-$(CONFIG_GPIO_SAMA5D2_PIOBU)	+= gpio-sama5d2-piobu.o
>  obj-$(CONFIG_GPIO_SCH311X)		+= gpio-sch311x.o
>  obj-$(CONFIG_GPIO_SCH)			+= gpio-sch.o
>  obj-$(CONFIG_GPIO_SIFIVE)		+= gpio-sifive.o
> +obj-$(CONFIG_GPIO_SIM)			+= gpio-sim.o
>  obj-$(CONFIG_GPIO_SIOX)			+= gpio-siox.o
>  obj-$(CONFIG_GPIO_SL28CPLD)		+= gpio-sl28cpld.o
>  obj-$(CONFIG_GPIO_SODAVILLE)		+= gpio-sodaville.o
> diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
> new file mode 100644
> index 000000000000..0ed297127bca
> --- /dev/null
> +++ b/drivers/gpio/gpio-sim.c
> @@ -0,0 +1,878 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * GPIO testing driver based on configfs.
> + *
> + * Copyright (C) 2021 Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/bitmap.h>
> +#include <linux/configfs.h>
> +#include <linux/device.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/idr.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/irq_sim.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <linux/string_helpers.h>
> +#include <linux/sysfs.h>
> +
> +#include "gpiolib.h"
> +
> +/*
> + * This normally should correspond with the number of attributes exposed over
> + * configfs + sentinel.
> + */
> +#define GPIO_SIM_MAX_PROP 4
> +
> +static DEFINE_IDA(gpio_sim_ida);
> +
> +struct gpio_sim_chip {
> +	struct gpio_chip gc;
> +	unsigned long *directions;
> +	unsigned long *values;
> +	unsigned long *pulls;
> +	struct irq_domain *irq_sim;
> +	struct mutex lock;
> +	struct attribute_group attr_group;
> +};
> +
> +struct gpio_sim_attribute {
> +	struct device_attribute dev_attr;
> +	unsigned int offset;
> +};
> +
> +static struct gpio_sim_attribute *
> +to_gpio_sim_attr(struct device_attribute *dev_attr)
> +{
> +	return container_of(dev_attr, struct gpio_sim_attribute, dev_attr);
> +}
> +
> +static int gpio_sim_apply_pull(struct gpio_sim_chip *chip,
> +			       unsigned int offset, int value)
> +{
> +	int curr_val, irq, irq_type, ret;
> +	struct gpio_desc *desc;
> +	struct gpio_chip *gc;
> +
> +	gc = &chip->gc;
> +	desc = &gc->gpiodev->descs[offset];
> +
> +	mutex_lock(&chip->lock);
> +
> +	if (test_bit(FLAG_REQUESTED, &desc->flags) &&
> +	    !test_bit(FLAG_IS_OUT, &desc->flags)) {
> +		curr_val = !!test_bit(offset, chip->values);
> +		if (curr_val == value)
> +			goto set_pull;
> +
> +		/*
> +		 * This is fine - it just means, nobody is listening
> +		 * for interrupts on this line, otherwise
> +		 * irq_create_mapping() would have been called from
> +		 * the to_irq() callback.
> +		 */
> +		irq = irq_find_mapping(chip->irq_sim, offset);
> +		if (!irq)
> +			goto set_value;
> +
> +		irq_type = irq_get_trigger_type(irq);
> +
> +		if ((value && (irq_type & IRQ_TYPE_EDGE_RISING)) ||
> +		    (!value && (irq_type & IRQ_TYPE_EDGE_FALLING))) {
> +			ret = irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING,
> +						    true);
> +			if (ret)
> +				goto set_pull;
> +		}
> +	}
> +
> +set_value:
> +	/* Change the value unless we're actively driving the line. */
> +	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
> +	    !test_bit(FLAG_IS_OUT, &desc->flags))
> +		__assign_bit(offset, chip->values, value);
> +
> +set_pull:
> +	__assign_bit(offset, chip->pulls, value);
> +	mutex_unlock(&chip->lock);
> +	return 0;
> +}
> +
> +static int gpio_sim_get(struct gpio_chip *gc, unsigned int offset)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +	int ret;
> +
> +	mutex_lock(&chip->lock);
> +	ret = !!test_bit(offset, chip->values);
> +	mutex_unlock(&chip->lock);
> +
> +	return ret;
> +}
> +
> +static void gpio_sim_set(struct gpio_chip *gc, unsigned int offset, int value)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	__assign_bit(offset, chip->values, value);
> +	mutex_unlock(&chip->lock);
> +}
> +
> +static int gpio_sim_get_multiple(struct gpio_chip *gc,
> +				 unsigned long *mask, unsigned long *bits)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	bitmap_copy(bits, chip->values, gc->ngpio);
> +	mutex_unlock(&chip->lock);
> +
> +	return 0;
> +}
> +
> +static void gpio_sim_set_multiple(struct gpio_chip *gc,
> +				  unsigned long *mask, unsigned long *bits)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	bitmap_copy(chip->values, bits, gc->ngpio);
> +	mutex_unlock(&chip->lock);
> +}
> +
> +static int gpio_sim_direction_output(struct gpio_chip *gc,
> +				     unsigned int offset, int value)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	__clear_bit(offset, chip->directions);
> +	__assign_bit(offset, chip->values, value);
> +	mutex_unlock(&chip->lock);
> +
> +	return 0;
> +}
> +
> +static int gpio_sim_direction_input(struct gpio_chip *gc, unsigned int offset)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	__set_bit(offset, chip->directions);
> +	mutex_unlock(&chip->lock);
> +
> +	return 0;
> +}
> +
> +static int gpio_sim_get_direction(struct gpio_chip *gc, unsigned int offset)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +	int direction;
> +
> +	mutex_lock(&chip->lock);
> +	direction = !!test_bit(offset, chip->directions);
> +	mutex_unlock(&chip->lock);
> +
> +	return direction ? GPIO_LINE_DIRECTION_IN : GPIO_LINE_DIRECTION_OUT;
> +}
> +
> +static int gpio_sim_set_config(struct gpio_chip *gc,
> +				  unsigned int offset, unsigned long config)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	switch (pinconf_to_config_param(config)) {
> +	case PIN_CONFIG_BIAS_PULL_UP:
> +		return gpio_sim_apply_pull(chip, offset, 1);
> +	case PIN_CONFIG_BIAS_PULL_DOWN:
> +		return gpio_sim_apply_pull(chip, offset, 0);
> +	default:
> +		break;
> +	}
> +
> +	return -ENOTSUPP;
> +}
> +
> +static int gpio_sim_to_irq(struct gpio_chip *gc, unsigned int offset)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	return irq_create_mapping(chip->irq_sim, offset);
> +}
> +
> +static void gpio_sim_free(struct gpio_chip *gc, unsigned int offset)
> +{
> +	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
> +
> +	mutex_lock(&chip->lock);
> +	__assign_bit(offset, chip->values, !!test_bit(offset, chip->pulls));
> +	mutex_unlock(&chip->lock);
> +}
> +
> +static ssize_t gpio_sim_sysfs_line_show(struct device *dev,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct gpio_sim_attribute *line_attr = to_gpio_sim_attr(attr);
> +	struct gpio_sim_chip *chip = dev_get_drvdata(dev);
> +	int ret;
> +
> +	mutex_lock(&chip->lock);
> +	ret = sprintf(buf, "%u\n", !!test_bit(line_attr->offset, chip->values));
> +	mutex_unlock(&chip->lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t gpio_sim_sysfs_line_store(struct device *dev,
> +					 struct device_attribute *attr,
> +					 const char *buf, size_t len)
> +{
> +	struct gpio_sim_attribute *line_attr = to_gpio_sim_attr(attr);
> +	struct gpio_sim_chip *chip = dev_get_drvdata(dev);
> +	int ret, val;
> +
> +	if (len > 2 || (buf[0] != '0' && buf[0] != '1'))
> +		return -EINVAL;
> +
> +	val = buf[0] == '0' ? 0 : 1;
> +
> +	ret = gpio_sim_apply_pull(chip, line_attr->offset, val);
> +	if (ret)
> +		return ret;
> +
> +	return len;
> +}
> +
> +static void gpio_sim_mutex_destroy(void *data)
> +{
> +	struct mutex *lock = data;
> +
> +	mutex_destroy(lock);
> +}
> +
> +static void gpio_sim_sysfs_remove(void *data)
> +{
> +	struct gpio_sim_chip *chip = data;
> +
> +	sysfs_remove_group(&chip->gc.parent->kobj, &chip->attr_group);
> +}
> +
> +static int gpio_sim_setup_sysfs(struct gpio_sim_chip *chip)
> +{
> +	unsigned int i, num_lines = chip->gc.ngpio;
> +	struct device *dev = chip->gc.parent;
> +	struct gpio_sim_attribute *line_attr;
> +	struct device_attribute *dev_attr;
> +	struct attribute **attrs;
> +	int ret;
> +
> +	attrs = devm_kcalloc(dev, sizeof(*attrs), num_lines + 1, GFP_KERNEL);
> +	if (!attrs)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < num_lines; i++) {
> +		line_attr = devm_kzalloc(dev, sizeof(*line_attr), GFP_KERNEL);
> +		if (!line_attr)
> +			return -ENOMEM;
> +
> +		line_attr->offset = i;
> +
> +		dev_attr = &line_attr->dev_attr;

> +		dev_attr->attr.name = devm_kasprintf(dev, GFP_KERNEL,
> +						     "gpio%u", i);

Reads better as one line.

> +		if (!dev_attr->attr.name)
> +			return -ENOMEM;
> +
> +		dev_attr->attr.mode = 0644;
> +
> +		dev_attr->show = gpio_sim_sysfs_line_show;
> +		dev_attr->store = gpio_sim_sysfs_line_store;
> +
> +		attrs[i] = &dev_attr->attr;
> +	}
> +
> +	chip->attr_group.name = "line-ctrl";
> +	chip->attr_group.attrs = attrs;
> +
> +	ret = sysfs_create_group(&dev->kobj, &chip->attr_group);
> +	if (ret)
> +		return ret;
> +
> +	return devm_add_action_or_reset(dev, gpio_sim_sysfs_remove, chip);
> +}
> +
> +static int gpio_sim_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct gpio_sim_chip *chip;
> +	struct gpio_chip *gc;
> +	const char *label;
> +	u32 num_lines;
> +	int ret;
> +
> +	ret = device_property_read_u32(dev, "gpio-sim,nr-gpios", &num_lines);
> +	if (ret)
> +		return ret;
> +
> +	ret = device_property_read_string(dev, "gpio-sim,label", &label);
> +	if (ret)
> +		label = dev_name(dev);
> +
> +	chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
> +	if (!chip)
> +		return -ENOMEM;
> +
> +	chip->directions = devm_bitmap_zalloc(dev, num_lines, GFP_KERNEL);

What's the point to have "z" variant here...

> +	if (!chip->directions)
> +		return -ENOMEM;
> +
> +	/* Default to input mode. */
> +	bitmap_fill(chip->directions, num_lines);

...followed by filling all 1:s here?

> +	chip->values = devm_bitmap_zalloc(dev, num_lines, GFP_KERNEL);
> +	if (!chip->values)
> +		return -ENOMEM;
> +
> +	chip->pulls = devm_bitmap_zalloc(dev, num_lines, GFP_KERNEL);
> +	if (!chip->pulls)
> +		return -ENOMEM;
> +
> +	chip->irq_sim = devm_irq_domain_create_sim(dev, NULL, num_lines);
> +	if (IS_ERR(chip->irq_sim))
> +		return PTR_ERR(chip->irq_sim);
> +
> +	mutex_init(&chip->lock);
> +	ret = devm_add_action_or_reset(dev, gpio_sim_mutex_destroy,
> +				       &chip->lock);
> +	if (ret)
> +		return ret;
> +
> +	gc = &chip->gc;
> +	gc->base = -1;
> +	gc->ngpio = num_lines;
> +	gc->label = label;
> +	gc->owner = THIS_MODULE;
> +	gc->parent = dev;
> +	gc->get = gpio_sim_get;
> +	gc->set = gpio_sim_set;
> +	gc->get_multiple = gpio_sim_get_multiple;
> +	gc->set_multiple = gpio_sim_set_multiple;
> +	gc->direction_output = gpio_sim_direction_output;
> +	gc->direction_input = gpio_sim_direction_input;
> +	gc->get_direction = gpio_sim_get_direction;
> +	gc->set_config = gpio_sim_set_config;
> +	gc->to_irq = gpio_sim_to_irq;
> +	gc->free = gpio_sim_free;
> +
> +	ret = devm_gpiochip_add_data(dev, gc, chip);
> +	if (ret)
> +		return ret;
> +
> +	/* Used by sysfs and configfs callbacks. */
> +	dev_set_drvdata(dev, chip);
> +
> +	ret = gpio_sim_setup_sysfs(chip);
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id gpio_sim_of_match[] = {
> +	{ .compatible = "gpio-simulator" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, gpio_sim_of_match);
> +
> +static struct platform_driver gpio_sim_driver = {
> +	.driver = {
> +		.name = "gpio-sim",
> +	},
> +	.probe = gpio_sim_probe,
> +};
> +
> +struct gpio_sim_chip_config {
> +	struct config_item item;
> +
> +	/*
> +	 * If pdev is NULL, the item is 'pending' (waiting for configuration).
> +	 * Once the pointer is assigned, the device has been created and the
> +	 * item is 'live'.
> +	 */
> +	struct platform_device *pdev;
> +
> +	/*
> +	 * Each configfs filesystem operation is protected with the subsystem
> +	 * mutex. Each separate attribute is protected with the buffer mutex.
> +	 * This structure however can be modified by callbacks of different
> +	 * attributes so we need another lock.
> +	 */
> +	struct mutex lock;
> +
> +	char label[32];
> +	unsigned int num_lines;
> +	char **line_names;
> +	unsigned int num_line_names;
> +};
> +
> +static struct gpio_sim_chip_config *
> +to_gpio_sim_chip_config(struct config_item *item)
> +{
> +	return container_of(item, struct gpio_sim_chip_config, item);
> +}
> +
> +static ssize_t gpio_sim_config_dev_name_show(struct config_item *item,
> +					     char *page)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	struct platform_device *pdev;
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +	pdev = config->pdev;
> +	if (pdev && device_is_bound(&pdev->dev))
> +		ret = sprintf(page, "%s\n", dev_name(&pdev->dev));
> +	else
> +		ret = -ENODEV;
> +	mutex_unlock(&config->lock);
> +
> +	return ret;
> +}
> +
> +CONFIGFS_ATTR_RO(gpio_sim_config_, dev_name);
> +
> +static ssize_t gpio_sim_config_chip_name_show(struct config_item *item,
> +					      char *page)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	struct platform_device *pdev;
> +	struct gpio_sim_chip *chip;
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +	pdev = config->pdev;
> +	if (pdev && device_is_bound(&pdev->dev)) {
> +		chip = dev_get_drvdata(&pdev->dev);
> +		ret = sprintf(page, "%s\n", dev_name(&chip->gc.gpiodev->dev));
> +	} else {
> +		ret = -ENODEV;
> +	}
> +	mutex_unlock(&config->lock);
> +
> +	return ret;
> +}
> +
> +CONFIGFS_ATTR_RO(gpio_sim_config_, chip_name);
> +
> +static ssize_t gpio_sim_config_label_show(struct config_item *item, char *page)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +	ret = sprintf(page, "%s\n", config->label);
> +	mutex_unlock(&config->lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t gpio_sim_config_label_store(struct config_item *item,
> +					   const char *page, size_t count)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	char *dup, *trimmed;
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +
> +	if (config->pdev) {
> +		mutex_unlock(&config->lock);
> +		return -EBUSY;
> +	}
> +
> +	dup = kstrndup(page, count, GFP_KERNEL);
> +	if (!dup) {
> +		mutex_unlock(&config->lock);
> +		return -ENOMEM;
> +	}
> +
> +	trimmed = strstrip(dup);
> +	ret = snprintf(config->label, sizeof(config->label), "%s", trimmed);
> +	kfree(dup);
> +	if (ret < 0) {
> +		mutex_unlock(&config->lock);
> +		return ret;
> +	}
> +
> +	mutex_unlock(&config->lock);
> +	return count;
> +}
> +
> +CONFIGFS_ATTR(gpio_sim_config_, label);
> +
> +static ssize_t gpio_sim_config_num_lines_show(struct config_item *item,
> +					      char *page)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +	ret = sprintf(page, "%u\n", config->num_lines);
> +	mutex_unlock(&config->lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t gpio_sim_config_num_lines_store(struct config_item *item,
> +					       const char *page, size_t count)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	unsigned int num_lines;
> +	int ret;
> +
> +	mutex_lock(&config->lock);
> +
> +	if (config->pdev) {
> +		mutex_unlock(&config->lock);
> +		return -EBUSY;
> +	}
> +
> +	ret = kstrtouint(page, 10, &num_lines);
> +	if (ret) {
> +		mutex_unlock(&config->lock);
> +		return ret;
> +	}
> +
> +	if (num_lines == 0) {
> +		mutex_unlock(&config->lock);
> +		return -EINVAL;
> +	}
> +
> +	config->num_lines = num_lines;
> +
> +	mutex_unlock(&config->lock);
> +	return count;
> +}
> +
> +CONFIGFS_ATTR(gpio_sim_config_, num_lines);
> +
> +static ssize_t gpio_sim_config_line_names_show(struct config_item *item,
> +					       char *page)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	int ret, i, written = 0;
> +
> +	mutex_lock(&config->lock);
> +
> +	if (!config->line_names) {
> +		mutex_unlock(&config->lock);
> +		return sprintf(page, "\n");
> +	}
> +
> +	for (i = 0; i < config->num_line_names; i++) {

> +		ret = sprintf(page + written,
> +			i < config->num_line_names - 1 ?
> +				"\"%s\", " : "\"%s\"\n",
> +			config->line_names[i] ?: "");

Indentation here looks not the best...

> +		if (ret < 0) {
> +			mutex_unlock(&config->lock);
> +			return ret;
> +		}
> +
> +		written += ret;
> +	}

> +	mutex_unlock(&config->lock);
> +	return written;
> +}
> +
> +static ssize_t gpio_sim_config_line_names_store(struct config_item *item,
> +						const char *page, size_t count)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	unsigned int num_new_names = 1, num_old_names, name_idx = 0;
> +	bool in_quote = false, got_comma = true;
> +	char **new_names, **old_names, *name, c;
> +	const char *start = page;
> +	size_t pos, name_len;
> +	int err = -EINVAL;
> +
> +	mutex_lock(&config->lock);
> +
> +	if (config->pdev) {
> +		mutex_unlock(&config->lock);
> +		return -EBUSY;
> +	}
> +
> +	/*
> +	 * Line names are stored in a pointer array so that we can easily
> +	 * pass them down to the GPIO subsystem in a "gpio-line-names"
> +	 * property.
> +	 *
> +	 * Line names must be passed as a list of quoted names separated by
> +	 * commas, for example: '"foo", "bar", "foobar"'.
> +	 */
> +
> +	for (pos = 0; pos < count; pos++) {
> +		/*
> +		 * Just count the commas and assume the number if strings
> +		 * equals the number of commas + 1. If the format is wrong
> +		 * we'll bail out anyway.
> +		 */
> +		if (page[pos] == ',')
> +			num_new_names++;
> +	}
> +
> +	new_names = kcalloc(num_new_names, sizeof(char *), GFP_KERNEL);
> +	if (!new_names) {
> +		mutex_unlock(&config->lock);
> +		return -ENOMEM;
> +	}
> +
> +	/*
> +	 * FIXME If anyone knows a better way to parse that - please let me
> +	 * know.
> +	 */

If comma can be replaced with ' ' (space) then why not to use next_arg() from
cmdline.c? I.o.w. do you have strong opinion why should we use comma here?

> +	for (pos = 0; pos < count; pos++) {
> +		c = page[pos];
> +
> +		if (in_quote) {
> +			if (c == '"') {
> +				/* This is the end of the name. */
> +				in_quote = got_comma = false;
> +				name_len = (page + pos) - start;
> +				if (name_len == 0) {
> +					/* Name is empty (passed as ""). */
> +					name_idx++;
> +					continue;
> +				}

> +				name = kzalloc(name_len + 1, GFP_KERNEL);
> +				if (!name) {
> +					err = -ENOMEM;
> +					goto err_out;
> +				}
> +
> +				memcpy(name, start, name_len);

kmemdup()/kstrndup() or so?

> +				new_names[name_idx++] = name;
> +			}
> +		} else {
> +			if (c == '"') {
> +				/* Enforce separating names with commas. */
> +				if (!got_comma)
> +					goto err_out;
> +
> +				start = page + pos + 1;
> +				in_quote = true;
> +			} else if (c == ',') {
> +				if (!got_comma)
> +					got_comma = true;
> +				else
> +					/* Double commas are not allowed. */
> +					goto err_out;
> +			} else if (!isspace(c)) {
> +				goto err_out;
> +			}
> +		}
> +	}
> +
> +	/*
> +	 * End of input sanity checks, must not have a comma at the end and
> +	 * must have finished scanning the last name.
> +	 */
> +	if (in_quote || got_comma)
> +		goto err_out;
> +
> +	old_names = config->line_names;
> +	num_old_names = config->num_line_names;
> +	config->line_names = new_names;
> +	config->num_line_names = num_new_names;
> +
> +	mutex_unlock(&config->lock);
> +	kfree_strarray(old_names, num_old_names);
> +	return count;
> +
> +err_out:
> +	mutex_unlock(&config->lock);
> +	kfree_strarray(new_names, name_idx);
> +	return err;
> +}
> +
> +CONFIGFS_ATTR(gpio_sim_config_, line_names);
> +
> +static struct configfs_attribute *gpio_sim_config_attrs[] = {
> +	&gpio_sim_config_attr_dev_name,
> +	&gpio_sim_config_attr_chip_name,
> +	&gpio_sim_config_attr_label,
> +	&gpio_sim_config_attr_num_lines,
> +	&gpio_sim_config_attr_line_names,
> +	NULL
> +};
> +
> +static void gpio_sim_chip_config_release(struct config_item *item)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +
> +	mutex_destroy(&config->lock);
> +	kfree_strarray(config->line_names, config->num_line_names);
> +	kfree(config);
> +}
> +
> +static struct configfs_item_operations gpio_sim_config_item_ops = {
> +	.release	= gpio_sim_chip_config_release,
> +};
> +
> +static const struct config_item_type gpio_sim_chip_config_type = {
> +	.ct_item_ops	= &gpio_sim_config_item_ops,
> +	.ct_attrs	= gpio_sim_config_attrs,
> +	.ct_owner	= THIS_MODULE,
> +};
> +
> +static struct config_item *
> +gpio_sim_config_make_item(struct config_group *group, const char *name)
> +{
> +	struct gpio_sim_chip_config *config;
> +
> +	config = kzalloc(sizeof(*config), GFP_KERNEL);
> +	if (!config)
> +		return ERR_PTR(-ENOMEM);
> +
> +	config_item_init_type_name(&config->item, name,
> +				   &gpio_sim_chip_config_type);
> +	config->num_lines = 1;
> +	mutex_init(&config->lock);
> +
> +	return &config->item;
> +}
> +
> +static int gpio_sim_config_commit_item(struct config_item *item)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	struct property_entry properties[GPIO_SIM_MAX_PROP];
> +	struct platform_device_info pdevinfo;
> +	struct platform_device *pdev;
> +	unsigned int prop_idx = 0;
> +
> +	memset(&pdevinfo, 0, sizeof(pdevinfo));
> +	memset(properties, 0, sizeof(properties));
> +
> +	mutex_lock(&config->lock);
> +
> +	properties[prop_idx++] = PROPERTY_ENTRY_U32("gpio-sim,nr-gpios",
> +						    config->num_lines);
> +
> +	if (config->label[0] != '\0')
> +		properties[prop_idx++] = PROPERTY_ENTRY_STRING("gpio-sim,label",
> +							       config->label);
> +
> +	if (config->line_names)
> +		properties[prop_idx++] = PROPERTY_ENTRY_STRING_ARRAY_LEN(
> +						"gpio-line-names",
> +						config->line_names,
> +						config->num_line_names);
> +
> +	pdevinfo.id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
> +	if (pdevinfo.id < 0) {
> +		mutex_unlock(&config->lock);
> +		return pdevinfo.id;
> +	}
> +
> +	pdevinfo.name = "gpio-sim";
> +	pdevinfo.properties = properties;
> +
> +	pdev = platform_device_register_full(&pdevinfo);
> +	if (IS_ERR(pdev)) {
> +		ida_free(&gpio_sim_ida, pdevinfo.id);
> +		mutex_unlock(&config->lock);
> +		return PTR_ERR(pdev);
> +	}
> +
> +	config->pdev = pdev;
> +	mutex_unlock(&config->lock);
> +
> +	return 0;
> +}
> +
> +static int gpio_sim_config_uncommit_item(struct config_item *item)
> +{
> +	struct gpio_sim_chip_config *config = to_gpio_sim_chip_config(item);
> +	int id;
> +
> +	mutex_lock(&config->lock);
> +	id = config->pdev->id;
> +	platform_device_unregister(config->pdev);
> +	config->pdev = NULL;

> +	ida_free(&gpio_sim_ida, id);

Isn't it atomic per se? I mean that IDA won't give the same ID until you free
it. I.o.w. why is it under the mutex?

> +	mutex_unlock(&config->lock);
> +
> +	return 0;
> +}
> +
> +static struct configfs_group_operations gpio_sim_config_group_ops = {
> +	.make_item	= gpio_sim_config_make_item,
> +	.commit_item	= gpio_sim_config_commit_item,
> +	.uncommit_item	= gpio_sim_config_uncommit_item,
> +};
> +
> +static const struct config_item_type gpio_sim_config_type = {
> +	.ct_group_ops	= &gpio_sim_config_group_ops,
> +	.ct_owner	= THIS_MODULE,
> +};
> +
> +static struct configfs_subsystem gpio_sim_config_subsys = {
> +	.su_group = {
> +		.cg_item = {
> +			.ci_namebuf	= "gpio-sim",
> +			.ci_type	= &gpio_sim_config_type,
> +		},
> +	},
> +};
> +
> +static int __init gpio_sim_init(void)
> +{
> +	int ret;
> +
> +	ret = platform_driver_register(&gpio_sim_driver);
> +	if (ret) {
> +		pr_err("Error %d while registering the platform driver\n", ret);
> +		return ret;
> +	}
> +
> +	config_group_init(&gpio_sim_config_subsys.su_group);
> +	mutex_init(&gpio_sim_config_subsys.su_mutex);
> +	ret = configfs_register_subsystem(&gpio_sim_config_subsys);
> +	if (ret) {
> +		pr_err("Error %d while registering the configfs subsystem %s\n",
> +		       ret, gpio_sim_config_subsys.su_group.cg_item.ci_namebuf);
> +		mutex_destroy(&gpio_sim_config_subsys.su_mutex);
> +		platform_driver_unregister(&gpio_sim_driver);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +module_init(gpio_sim_init);
> +
> +static void __exit gpio_sim_exit(void)
> +{
> +	configfs_unregister_subsystem(&gpio_sim_config_subsys);
> +	mutex_destroy(&gpio_sim_config_subsys.su_mutex);
> +	platform_driver_unregister(&gpio_sim_driver);
> +}
> +module_exit(gpio_sim_exit);
> +
> +MODULE_AUTHOR("Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("GPIO Simulator Module");
> +MODULE_LICENSE("GPL");
> -- 
> 2.29.1
> 

-- 
With Best Regards,
Andy Shevchenko