linux/drivers/nvmem/core.c

// SPDX-License-Identifier: GPL-2.0
/*
 * nvmem framework core.
 *
 * Copyright (C) 2015 Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
 * Copyright (C) 2013 Maxime Ripard <maxime.ripard@free-electrons.com>
 */

#include <linux/device.h>
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/kref.h>
#include <linux/module.h>
#include <linux/nvmem-consumer.h>
#include <linux/nvmem-provider.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>
#include <linux/slab.h>
#include "nvmem.h"

struct nvmem_cell {
	const char		*name;
	int			offset;
	int			bytes;
	int			bit_offset;
	int			nbits;
	struct device_node	*np;
	struct nvmem_device	*nvmem;
	struct list_head	node;
};

static DEFINE_MUTEX(nvmem_mutex);
static DEFINE_IDA(nvmem_ida);

static DEFINE_MUTEX(nvmem_cell_mutex);
static LIST_HEAD(nvmem_cell_tables);

static DEFINE_MUTEX(nvmem_lookup_mutex);
static LIST_HEAD(nvmem_lookup_list);

static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);


static int nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
			  void *val, size_t bytes)
{
	if (nvmem->reg_read)
		return nvmem->reg_read(nvmem->priv, offset, val, bytes);

	return -EINVAL;
}

static int nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
			   void *val, size_t bytes)
{
	int ret;

	if (nvmem->reg_write) {
		gpiod_set_value_cansleep(nvmem->wp_gpio, 0);
		ret = nvmem->reg_write(nvmem->priv, offset, val, bytes);
		gpiod_set_value_cansleep(nvmem->wp_gpio, 1);
		return ret;
	}

	return -EINVAL;
}

static void nvmem_release(struct device *dev)
{
	struct nvmem_device *nvmem = to_nvmem_device(dev);

	ida_simple_remove(&nvmem_ida, nvmem->id);
	gpiod_put(nvmem->wp_gpio);
	kfree(nvmem);
}

static const struct device_type nvmem_provider_type = {
	.release	= nvmem_release,
};

static struct bus_type nvmem_bus_type = {
	.name		= "nvmem",
};

static void nvmem_cell_drop(struct nvmem_cell *cell)
{
	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_REMOVE, cell);
	mutex_lock(&nvmem_mutex);
	list_del(&cell->node);
	mutex_unlock(&nvmem_mutex);
	of_node_put(cell->np);
	kfree_const(cell->name);
	kfree(cell);
}

static void nvmem_device_remove_all_cells(const struct nvmem_device *nvmem)
{
	struct nvmem_cell *cell, *p;

	list_for_each_entry_safe(cell, p, &nvmem->cells, node)
		nvmem_cell_drop(cell);
}

static void nvmem_cell_add(struct nvmem_cell *cell)
{
	mutex_lock(&nvmem_mutex);
	list_add_tail(&cell->node, &cell->nvmem->cells);
	mutex_unlock(&nvmem_mutex);
	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_ADD, cell);
}

static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
				   const struct nvmem_cell_info *info,
				   struct nvmem_cell *cell)
{
	cell->nvmem = nvmem;
	cell->offset = info->offset;
	cell->bytes = info->bytes;
	cell->name = kstrdup_const(info->name, GFP_KERNEL);
	if (!cell->name)
		return -ENOMEM;

	cell->bit_offset = info->bit_offset;
	cell->nbits = info->nbits;

	if (cell->nbits)
		cell->bytes = DIV_ROUND_UP(cell->nbits + cell->bit_offset,
					   BITS_PER_BYTE);

	if (!IS_ALIGNED(cell->offset, nvmem->stride)) {
		dev_err(&nvmem->dev,
			"cell %s unaligned to nvmem stride %d\n",
			cell->name, nvmem->stride);
		return -EINVAL;
	}

	return 0;
}

/**
 * nvmem_add_cells() - Add cell information to an nvmem device
 *
 * @nvmem: nvmem device to add cells to.
 * @info: nvmem cell info to add to the device
 * @ncells: number of cells in info
 *
 * Return: 0 or negative error code on failure.
 */
static int nvmem_add_cells(struct nvmem_device *nvmem,
		    const struct nvmem_cell_info *info,
		    int ncells)
{
	struct nvmem_cell **cells;
	int i, rval;

	cells = kcalloc(ncells, sizeof(*cells), GFP_KERNEL);
	if (!cells)
		return -ENOMEM;

	for (i = 0; i < ncells; i++) {
		cells[i] = kzalloc(sizeof(**cells), GFP_KERNEL);
		if (!cells[i]) {
			rval = -ENOMEM;
			goto err;
		}

		rval = nvmem_cell_info_to_nvmem_cell(nvmem, &info[i], cells[i]);
		if (rval) {
			kfree(cells[i]);
			goto err;
		}

		nvmem_cell_add(cells[i]);
	}

	/* remove tmp array */
	kfree(cells);

	return 0;
err:
	while (i--)
		nvmem_cell_drop(cells[i]);

	kfree(cells);

	return rval;
}

/**
 * nvmem_register_notifier() - Register a notifier block for nvmem events.
 *
 * @nb: notifier block to be called on nvmem events.
 *
 * Return: 0 on success, negative error number on failure.
 */
int nvmem_register_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_register(&nvmem_notifier, nb);
}
EXPORT_SYMBOL_GPL(nvmem_register_notifier);

/**
 * nvmem_unregister_notifier() - Unregister a notifier block for nvmem events.
 *
 * @nb: notifier block to be unregistered.
 *
 * Return: 0 on success, negative error number on failure.
 */
int nvmem_unregister_notifier(struct notifier_block *nb)
{
	return blocking_notifier_chain_unregister(&nvmem_notifier, nb);
}
EXPORT_SYMBOL_GPL(nvmem_unregister_notifier);

static int nvmem_add_cells_from_table(struct nvmem_device *nvmem)
{
	const struct nvmem_cell_info *info;
	struct nvmem_cell_table *table;
	struct nvmem_cell *cell;
	int rval = 0, i;

	mutex_lock(&nvmem_cell_mutex);
	list_for_each_entry(table, &nvmem_cell_tables, node) {
		if (strcmp(nvmem_dev_name(nvmem), table->nvmem_name) == 0) {
			for (i = 0; i < table->ncells; i++) {
				info = &table->cells[i];

				cell = kzalloc(sizeof(*cell), GFP_KERNEL);
				if (!cell) {
					rval = -ENOMEM;
					goto out;
				}

				rval = nvmem_cell_info_to_nvmem_cell(nvmem,
								     info,
								     cell);
				if (rval) {
					kfree(cell);
					goto out;
				}

				nvmem_cell_add(cell);
			}
		}
	}

out:
	mutex_unlock(&nvmem_cell_mutex);
	return rval;
}

static struct nvmem_cell *
nvmem_find_cell_by_name(struct nvmem_device *nvmem, const char *cell_id)
{
	struct nvmem_cell *iter, *cell = NULL;

	mutex_lock(&nvmem_mutex);
	list_for_each_entry(iter, &nvmem->cells, node) {
		if (strcmp(cell_id, iter->name) == 0) {
			cell = iter;
			break;
		}
	}
	mutex_unlock(&nvmem_mutex);

	return cell;
}

static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
{
	struct device_node *parent, *child;
	struct device *dev = &nvmem->dev;
	struct nvmem_cell *cell;
	const __be32 *addr;
	int len;

	parent = dev->of_node;

	for_each_child_of_node(parent, child) {
		addr = of_get_property(child, "reg", &len);
		if (!addr || (len < 2 * sizeof(u32))) {
			dev_err(dev, "nvmem: invalid reg on %pOF\n", child);
			return -EINVAL;
		}

		cell = kzalloc(sizeof(*cell), GFP_KERNEL);
		if (!cell)
			return -ENOMEM;

		cell->nvmem = nvmem;
		cell->np = of_node_get(child);
		cell->offset = be32_to_cpup(addr++);
		cell->bytes = be32_to_cpup(addr);
		cell->name = kasprintf(GFP_KERNEL, "%pOFn", child);

		addr = of_get_property(child, "bits", &len);
		if (addr && len == (2 * sizeof(u32))) {
			cell->bit_offset = be32_to_cpup(addr++);
			cell->nbits = be32_to_cpup(addr);
		}

		if (cell->nbits)
			cell->bytes = DIV_ROUND_UP(
					cell->nbits + cell->bit_offset,
					BITS_PER_BYTE);

		if (!IS_ALIGNED(cell->offset, nvmem->stride)) {
			dev_err(dev, "cell %s unaligned to nvmem stride %d\n",
				cell->name, nvmem->stride);
			/* Cells already added will be freed later. */
			kfree_const(cell->name);
			kfree(cell);
			return -EINVAL;
		}

		nvmem_cell_add(cell);
	}

	return 0;
}

/**
 * nvmem_register() - Register a nvmem device for given nvmem_config.
 * Also creates an binary entry in /sys/bus/nvmem/devices/dev-name/nvmem
 *
 * @config: nvmem device configuration with which nvmem device is created.
 *
 * Return: Will be an ERR_PTR() on error or a valid pointer to nvmem_device
 * on success.
 */

struct nvmem_device *nvmem_register(const struct nvmem_config *config)
{
	struct nvmem_device *nvmem;
	int rval;

	if (!config->dev)
		return ERR_PTR(-EINVAL);

	if (!config->reg_read && !config->reg_write)
		return ERR_PTR(-EINVAL);

	nvmem = kzalloc(sizeof(*nvmem), GFP_KERNEL);
	if (!nvmem)
		return ERR_PTR(-ENOMEM);

	rval  = ida_simple_get(&nvmem_ida, 0, 0, GFP_KERNEL);
	if (rval < 0) {
		kfree(nvmem);
		return ERR_PTR(rval);
	}

	if (config->wp_gpio)
		nvmem->wp_gpio = config->wp_gpio;
	else
		nvmem->wp_gpio = gpiod_get_optional(config->dev, "wp",
						    GPIOD_OUT_HIGH);
	if (IS_ERR(nvmem->wp_gpio)) {
		ida_simple_remove(&nvmem_ida, nvmem->id);
		rval = PTR_ERR(nvmem->wp_gpio);
		kfree(nvmem);
		return ERR_PTR(rval);
	}

	kref_init(&nvmem->refcnt);
	INIT_LIST_HEAD(&nvmem->cells);

	nvmem->id = rval;
	nvmem->owner = config->owner;
	if (!nvmem->owner && config->dev->driver)
		nvmem->owner = config->dev->driver->owner;
	nvmem->stride = config->stride ?: 1;
	nvmem->word_size = config->word_size ?: 1;
	nvmem->size = config->size;
	nvmem->dev.type = &nvmem_provider_type;
	nvmem->dev.bus = &nvmem_bus_type;
	nvmem->dev.parent = config->dev;
	nvmem->root_only = config->root_only;
	nvmem->priv = config->priv;
	nvmem->type = config->type;
	nvmem->reg_read = config->reg_read;
	nvmem->reg_write = config->reg_write;
	if (!config->no_of_node)
		nvmem->dev.of_node = config->dev->of_node;

	if (config->id == -1 && config->name) {
		dev_set_name(&nvmem->dev, "%s", config->name);
	} else {
		dev_set_name(&nvmem->dev, "%s%d",
			     config->name ? : "nvmem",
			     config->name ? config->id : nvmem->id);
	}

	nvmem->read_only = device_property_present(config->dev, "read-only") ||
			   config->read_only || !nvmem->reg_write;

	nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);

	dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);

	rval = device_register(&nvmem->dev);
	if (rval)
		goto err_put_device;

	if (config->compat) {
		rval = nvmem_sysfs_setup_compat(nvmem, config);
		if (rval)
			goto err_device_del;
	}

	if (config->cells) {
		rval = nvmem_add_cells(nvmem, config->cells, config->ncells);
		if (rval)
			goto err_teardown_compat;
	}

	rval = nvmem_add_cells_from_table(nvmem);
	if (rval)
		goto err_remove_cells;

	rval = nvmem_add_cells_from_of(nvmem);
	if (rval)
		goto err_remove_cells;

	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);

	return nvmem;

err_remove_cells:
	nvmem_device_remove_all_cells(nvmem);
err_teardown_compat:
	if (config->compat)
		nvmem_sysfs_remove_compat(nvmem, config);
err_device_del:
	device_del(&nvmem->dev);
err_put_device:
	put_device(&nvmem->dev);

	return ERR_PTR(rval);
}
EXPORT_SYMBOL_GPL(nvmem_register);

static void nvmem_device_release(struct kref *kref)
{
	struct nvmem_device *nvmem;

	nvmem = container_of(kref, struct nvmem_device, refcnt);

	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_REMOVE, nvmem);

	if (nvmem->flags & FLAG_COMPAT)
		device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);

	nvmem_device_remove_all_cells(nvmem);
	device_unregister(&nvmem->dev);
}

/**
 * nvmem_unregister() - Unregister previously registered nvmem device
 *
 * @nvmem: Pointer to previously registered nvmem device.
 */
void nvmem_unregister(struct nvmem_device *nvmem)
{
	kref_put(&nvmem->refcnt, nvmem_device_release);
}
EXPORT_SYMBOL_GPL(nvmem_unregister);

static void devm_nvmem_release(struct device *dev, void *res)
{
	nvmem_unregister(*(struct nvmem_device **)res);
}

/**
 * devm_nvmem_register() - Register a managed nvmem device for given
 * nvmem_config.
 * Also creates an binary entry in /sys/bus/nvmem/devices/dev-name/nvmem
 *
 * @dev: Device that uses the nvmem device.
 * @config: nvmem device configuration with which nvmem device is created.
 *
 * Return: Will be an ERR_PTR() on error or a valid pointer to nvmem_device
 * on success.
 */
struct nvmem_device *devm_nvmem_register(struct device *dev,
					 const struct nvmem_config *config)
{
	struct nvmem_device **ptr, *nvmem;

	ptr = devres_alloc(devm_nvmem_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
		return ERR_PTR(-ENOMEM);

	nvmem = nvmem_register(config);

	if (!IS_ERR(nvmem)) {
		*ptr = nvmem;
		devres_add(dev, ptr);
	} else {
		devres_free(ptr);
	}

	return nvmem;
}
EXPORT_SYMBOL_GPL(devm_nvmem_register);

static int devm_nvmem_match(struct device *dev, void *res, void *data)
{
	struct nvmem_device **r = res;

	return *r == data;
}

/**
 * devm_nvmem_unregister() - Unregister previously registered managed nvmem
 * device.
 *
 * @dev: Device that uses the nvmem device.
 * @nvmem: Pointer to previously registered nvmem device.
 *
 * Return: Will be an negative on error or a zero on success.
 */
int devm_nvmem_unregister(struct device *dev, struct nvmem_device *nvmem)
{
	return devres_release(dev, devm_nvmem_release, devm_nvmem_match, nvmem);
}
EXPORT_SYMBOL(devm_nvmem_unregister);

static struct nvmem_device *__nvmem_device_get(void *data,
			int (*match)(struct device *dev, const void *data))
{
	struct nvmem_device *nvmem = NULL;
	struct device *dev;

	mutex_lock(&nvmem_mutex);
	dev = bus_find_device(&nvmem_bus_type, NULL, data, match);
	if (dev)
		nvmem = to_nvmem_device(dev);
	mutex_unlock(&nvmem_mutex);
	if (!nvmem)
		return ERR_PTR(-EPROBE_DEFER);

	if (!try_module_get(nvmem->owner)) {
		dev_err(&nvmem->dev,
			"could not increase module refcount for cell %s\n",
			nvmem_dev_name(nvmem));

		put_device(&nvmem->dev);
		return ERR_PTR(-EINVAL);
	}

	kref_get(&nvmem->refcnt);

	return nvmem;
}

static void __nvmem_device_put(struct nvmem_device *nvmem)
{
	put_device(&nvmem->dev);
	module_put(nvmem->owner);
	kref_put(&nvmem->refcnt, nvmem_device_release);
}

#if IS_ENABLED(CONFIG_OF)
/**
 * of_nvmem_device_get() - Get nvmem device from a given id
 *
 * @np: Device tree node that uses the nvmem device.
 * @id: nvmem name from nvmem-names property.
 *
 * Return: ERR_PTR() on error or a valid pointer to a struct nvmem_device
 * on success.
 */
struct nvmem_device *of_nvmem_device_get(struct device_node *np, const char *id)
{

	struct device_node *nvmem_np;
	int index = 0;

	if (id)
		index = of_property_match_string(np, "nvmem-names", id);

	nvmem_np = of_parse_phandle(np, "nvmem", index);
	if (!nvmem_np)
		return ERR_PTR(-ENOENT);

	return __nvmem_device_get(nvmem_np, device_match_of_node);
}
EXPORT_SYMBOL_GPL(of_nvmem_device_get);
#endif

/**
 * nvmem_device_get() - Get nvmem device from a given id
 *
 * @dev: Device that uses the nvmem device.
 * @dev_name: name of the requested nvmem device.
 *
 * Return: ERR_PTR() on error or a valid pointer to a struct nvmem_device
 * on success.
 */
struct nvmem_device *nvmem_device_get(struct device *dev, const char *dev_name)
{
	if (dev->of_node) { /* try dt first */
		struct nvmem_device *nvmem;

		nvmem = of_nvmem_device_get(dev->of_node, dev_name);

		if (!IS_ERR(nvmem) || PTR_ERR(nvmem) == -EPROBE_DEFER)
			return nvmem;

	}

	return __nvmem_device_get((void *)dev_name, device_match_name);
}
EXPORT_SYMBOL_GPL(nvmem_device_get);

/**
 * nvmem_device_find() - Find nvmem device with matching function
 *
 * @data: Data to pass to match function
 * @match: Callback function to check device
 *
 * Return: ERR_PTR() on error or a valid pointer to a struct nvmem_device
 * on success.
 */
struct nvmem_device *nvmem_device_find(void *data,
			int (*match)(struct device *dev, const void *data))
{
	return __nvmem_device_get(data, match);
}
EXPORT_SYMBOL_GPL(nvmem_device_find);

static int devm_nvmem_device_match(struct device *dev, void *res, void *data)
{
	struct nvmem_device **nvmem = res;

	if (WARN_ON(!nvmem || !*nvmem))
		return 0;

	return *nvmem == data;
}

static void devm_nvmem_device_release(struct device *dev, void *res)
{
	nvmem_device_put(*(struct nvmem_device **)res);
}

/**
 * devm_nvmem_device_put() - put alredy got nvmem device
 *
 * @dev: Device that uses the nvmem device.
 * @nvmem: pointer to nvmem device allocated by devm_nvmem_cell_get(),
 * that needs to be released.
 */
void devm_nvmem_device_put(struct device *dev, struct nvmem_device *nvmem)
{
	int ret;

	ret = devres_release(dev, devm_nvmem_device_release,
			     devm_nvmem_device_match, nvmem);

	WARN_ON(ret);
}
EXPORT_SYMBOL_GPL(devm_nvmem_device_put);

/**
 * nvmem_device_put() - put alredy got nvmem device
 *
 * @nvmem: pointer to nvmem device that needs to be released.
 */
void nvmem_device_put(struct nvmem_device *nvmem)
{
	__nvmem_device_put(nvmem);
}
EXPORT_SYMBOL_GPL(nvmem_device_put);

/**
 * devm_nvmem_device_get() - Get nvmem cell of device form a given id
 *
 * @dev: Device that requests the nvmem device.
 * @id: name id for the requested nvmem device.
 *
 * Return: ERR_PTR() on error or a valid pointer to a struct nvmem_cell
 * on success.  The nvmem_cell will be freed by the automatically once the
 * device is freed.
 */
struct nvmem_device *devm_nvmem_device_get(struct device *dev, const char *id)
{
	struct nvmem_device **ptr, *nvmem;

	ptr = devres_alloc(devm_nvmem_device_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
		return ERR_PTR(-ENOMEM);

	nvmem = nvmem_device_get(dev, id);
	if (!IS_ERR(nvmem)) {
		*ptr = nvmem;
		devres_add(dev, ptr);
	} else {
		devres_free(ptr);
	}

	return nvmem;
}
EXPORT_SYMBOL_GPL(devm_nvmem_device_get);

static struct nvmem_cell *
nvmem_cell_get_from_lookup(struct device *dev, const char *con_id)
{
	struct nvmem_cell *cell = ERR_PTR(-ENOENT);
	struct nvmem_cell_lookup *lookup;
	struct nvmem_device *nvmem;
	const char *dev_id;

	if (!dev)
		return ERR_PTR(-EINVAL);

	dev_id = dev_name(dev);

	mutex_lock(&nvmem_lookup_mutex);

	list_for_each_entry(lookup, &nvmem_lookup_list, node) {
		if ((strcmp(lookup->dev_id, dev_id) == 0) &&
		    (strcmp(lookup->con_id, con_id) == 0)) {
			/* This is the right entry. */
			nvmem = __nvmem_device_get((void *)lookup->nvmem_name,
						   device_match_name);
			if (IS_ERR(nvmem)) {
				/* Provider may not be registered yet. */
				cell = ERR_CAST(nvmem);
				break;
			}

			cell = nvmem_find_cell_by_name(nvmem,
						       lookup->cell_name);
			if (!cell) {
				__nvmem_device_put(nvmem);
				cell = ERR_PTR(-ENOENT);
			}
			break;
		}
	}

	mutex_unlock(&nvmem_lookup_mutex);
	return cell;
}

#if IS_ENABLED(CONFIG_OF)
static struct nvmem_cell *
nvmem_find_cell_by_node(struct nvmem_device *nvmem, struct device_node *np)
{
	struct nvmem_cell *iter, *cell = NULL;

	mutex_lock(&nvmem_mutex);
	list_for_each_entry(iter, &nvmem->cells, node) {
		if (np == iter->np) {
			cell = iter;
			break;
		}
	}
	mutex_unlock(&nvmem_mutex);

	return cell;
}

/**
 * of_nvmem_cell_get() - Get a nvmem cell from given device node and cell id
 *
 * @np: Device tree node that uses the nvmem cell.
 * @id: nvmem cell name from nvmem-cell-names property, or NULL
 *      for the cell at index 0 (the lone cell with no accompanying
 *      nvmem-cell-names property).
 *
 * Return: Will be an ERR_PTR() on error or a valid pointer
 * to a struct nvmem_cell.  The nvmem_cell will be freed by the
 * nvmem_cell_put().
 */
struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
{
	struct device_node *cell_np, *nvmem_np;
	struct nvmem_device *nvmem;
	struct nvmem_cell *cell;
	int index = 0;

	/* if cell name exists, find index to the name */
	if (id)
		index = of_property_match_string(np, "nvmem-cell-names", id);

	cell_np = of_parse_phandle(np, "nvmem-cells", index);
	if (!cell_np)
		return ERR_PTR(-ENOENT);

	nvmem_np = of_get_next_parent(cell_np);
	if (!nvmem_np)
		return ERR_PTR(-EINVAL);

	nvmem = __nvmem_device_get(nvmem_np, device_match_of_node);
	of_node_put(nvmem_np);
	if (IS_ERR(nvmem))
		return ERR_CAST(nvmem);

	cell = nvmem_find_cell_by_node(nvmem, cell_np);
	if (!cell) {
		__nvmem_device_put(nvmem);
		return ERR_PTR(-ENOENT);
	}

	return cell;
}
EXPORT_SYMBOL_GPL(of_nvmem_cell_get);
#endif

/**
 * nvmem_cell_get() - Get nvmem cell of device form a given cell name
 *
 * @dev: Device that requests the nvmem cell.
 * @id: nvmem cell name to get (this corresponds with the name from the
 *      nvmem-cell-names property for DT systems and with the con_id from
 *      the lookup entry for non-DT systems).
 *
 * Return: Will be an ERR_PTR() on error or a valid pointer
 * to a struct nvmem_cell.  The nvmem_cell will be freed by the
 * nvmem_cell_put().
 */
struct nvmem_cell *nvmem_cell_get(struct device *dev, const char *id)
{
	struct nvmem_cell *cell;

	if (dev->of_node) { /* try dt first */
		cell = of_nvmem_cell_get(dev->of_node, id);
		if (!IS_ERR(cell) || PTR_ERR(cell) == -EPROBE_DEFER)
			return cell;
	}

	/* NULL cell id only allowed for device tree; invalid otherwise */
	if (!id)
		return ERR_PTR(-EINVAL);

	return nvmem_cell_get_from_lookup(dev, id);
}
EXPORT_SYMBOL_GPL(nvmem_cell_get);

static void devm_nvmem_cell_release(struct device *dev, void *res)
{
	nvmem_cell_put(*(struct nvmem_cell **)res);
}

/**
 * devm_nvmem_cell_get() - Get nvmem cell of device form a given id
 *
 * @dev: Device that requests the nvmem cell.
 * @id: nvmem cell name id to get.
 *
 * Return: Will be an ERR_PTR() on error or a valid pointer
 * to a struct nvmem_cell.  The nvmem_cell will be freed by the
 * automatically once the device is freed.
 */
struct nvmem_cell *devm_nvmem_cell_get(struct device *dev, const char *id)
{
	struct nvmem_cell **ptr, *cell;

	ptr = devres_alloc(devm_nvmem_cell_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
		return ERR_PTR(-ENOMEM);

	cell = nvmem_cell_get(dev, id);
	if (!IS_ERR(cell)) {
		*ptr = cell;
		devres_add(dev, ptr);
	} else {
		devres_free(ptr);
	}

	return cell;
}
EXPORT_SYMBOL_GPL(devm_nvmem_cell_get);

static int devm_nvmem_cell_match(struct device *dev, void *res, void *data)
{
	struct nvmem_cell **c = res;

	if (WARN_ON(!c || !*c))
		return 0;

	return *c == data;
}

/**
 * devm_nvmem_cell_put() - Release previously allocated nvmem cell
 * from devm_nvmem_cell_get.
 *
 * @dev: Device that requests the nvmem cell.
 * @cell: Previously allocated nvmem cell by devm_nvmem_cell_get().
 */
void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell)
{
	int ret;

	ret = devres_release(dev, devm_nvmem_cell_release,
				devm_nvmem_cell_match, cell);

	WARN_ON(ret);
}
EXPORT_SYMBOL(devm_nvmem_cell_put);

/**
 * nvmem_cell_put() - Release previously allocated nvmem cell.
 *
 * @cell: Previously allocated nvmem cell by nvmem_cell_get().
 */
void nvmem_cell_put(struct nvmem_cell *cell)
{
	struct nvmem_device *nvmem = cell->nvmem;

	__nvmem_device_put(nvmem);
}
EXPORT_SYMBOL_GPL(nvmem_cell_put);

static void nvmem_shift_read_buffer_in_place(struct nvmem_cell *cell, void *buf)
{
	u8 *p, *b;
	int i, extra, bit_offset = cell->bit_offset;

	p = b = buf;
	if (bit_offset) {
		/* First shift */
		*b++ >>= bit_offset;

		/* setup rest of the bytes if any */
		for (i = 1; i < cell->bytes; i++) {
			/* Get bits from next byte and shift them towards msb */
			*p |= *b << (BITS_PER_BYTE - bit_offset);

			p = b;
			*b++ >>= bit_offset;
		}
	} else {
		/* point to the msb */
		p += cell->bytes - 1;
	}

	/* result fits in less bytes */
	extra = cell->bytes - DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE);
	while (--extra >= 0)
		*p-- = 0;

	/* clear msb bits if any leftover in the last byte */
	*p &= GENMASK((cell->nbits%BITS_PER_BYTE) - 1, 0);
}

static int __nvmem_cell_read(struct nvmem_device *nvmem,
		      struct nvmem_cell *cell,
		      void *buf, size_t *len)
{
	int rc;

	rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->bytes);

	if (rc)
		return rc;

	/* shift bits in-place */
	if (cell->bit_offset || cell->nbits)
		nvmem_shift_read_buffer_in_place(cell, buf);

	if (len)
		*len = cell->bytes;

	return 0;
}

/**
 * nvmem_cell_read() - Read a given nvmem cell
 *
 * @cell: nvmem cell to be read.
 * @len: pointer to length of cell which will be populated on successful read;
 *	 can be NULL.
 *
 * Return: ERR_PTR() on error or a valid pointer to a buffer on success. The
 * buffer should be freed by the consumer with a kfree().
 */
void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len)
{
	struct nvmem_device *nvmem = cell->nvmem;
	u8 *buf;
	int rc;

	if (!nvmem)
		return ERR_PTR(-EINVAL);

	buf = kzalloc(cell->bytes, GFP_KERNEL);
	if (!buf)
		return ERR_PTR(-ENOMEM);

	rc = __nvmem_cell_read(nvmem, cell, buf, len);
	if (rc) {
		kfree(buf);
		return ERR_PTR(rc);
	}

	return buf;
}
EXPORT_SYMBOL_GPL(nvmem_cell_read);

static void *nvmem_cell_prepare_write_buffer(struct nvmem_cell *cell,
					     u8 *_buf, int len)
{
	struct nvmem_device *nvmem = cell->nvmem;
	int i, rc, nbits, bit_offset = cell->bit_offset;
	u8 v, *p, *buf, *b, pbyte, pbits;

	nbits = cell->nbits;
	buf = kzalloc(cell->bytes, GFP_KERNEL);
	if (!buf)
		return ERR_PTR(-ENOMEM);

	memcpy(buf, _buf, len);
	p = b = buf;

	if (bit_offset) {
		pbyte = *b;
		*b <<= bit_offset;

		/* setup the first byte with lsb bits from nvmem */
		rc = nvmem_reg_read(nvmem, cell->offset, &v, 1);
		if (rc)
			goto err;
		*b++ |= GENMASK(bit_offset - 1, 0) & v;

		/* setup rest of the byte if any */
		for (i = 1; i < cell->bytes; i++) {
			/* Get last byte bits and shift them towards lsb */
			pbits = pbyte >> (BITS_PER_BYTE - 1 - bit_offset);
			pbyte = *b;
			p = b;
			*b <<= bit_offset;
			*b++ |= pbits;
		}
	}

	/* if it's not end on byte boundary */
	if ((nbits + bit_offset) % BITS_PER_BYTE) {
		/* setup the last byte with msb bits from nvmem */
		rc = nvmem_reg_read(nvmem,
				    cell->offset + cell->bytes - 1, &v, 1);
		if (rc)
			goto err;
		*p |= GENMASK(7, (nbits + bit_offset) % BITS_PER_BYTE) & v;

	}

	return buf;
err:
	kfree(buf);
	return ERR_PTR(rc);
}

/**
 * nvmem_cell_write() - Write to a given nvmem cell
 *
 * @cell: nvmem cell to be written.
 * @buf: Buffer to be written.
 * @len: length of buffer to be written to nvmem cell.
 *
 * Return: length of bytes written or negative on failure.
 */
int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len)
{
	struct nvmem_device *nvmem = cell->nvmem;
	int rc;

	if (!nvmem || nvmem->read_only ||
	    (cell->bit_offset == 0 && len != cell->bytes))
		return -EINVAL;

	if (cell->bit_offset || cell->nbits) {
		buf = nvmem_cell_prepare_write_buffer(cell, buf, len);
		if (IS_ERR(buf))
			return PTR_ERR(buf);
	}

	rc = nvmem_reg_write(nvmem, cell->offset, buf, cell->bytes);

	/* free the tmp buffer */
	if (cell->bit_offset || cell->nbits)
		kfree(buf);

	if (rc)
		return rc;

	return len;
}
EXPORT_SYMBOL_GPL(nvmem_cell_write);

static int nvmem_cell_read_common(struct device *dev, const char *cell_id,
				  void *val, size_t count)
{
	struct nvmem_cell *cell;
	void *buf;
	size_t len;

	cell = nvmem_cell_get(dev, cell_id);
	if (IS_ERR(cell))
		return PTR_ERR(cell);

	buf = nvmem_cell_read(cell, &len);
	if (IS_ERR(buf)) {
		nvmem_cell_put(cell);
		return PTR_ERR(buf);
	}
	if (len != count) {
		kfree(buf);
		nvmem_cell_put(cell);
		return -EINVAL;
	}
	memcpy(val, buf, count);
	kfree(buf);
	nvmem_cell_put(cell);

	return 0;
}

/**
 * nvmem_cell_read_u16() - Read a cell value as an u16
 *
 * @dev: Device that requests the nvmem cell.
 * @cell_id: Name of nvmem cell to read.
 * @val: pointer to output value.
 *
 * Return: 0 on success or negative errno.
 */
int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val)
{
	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
}
EXPORT_SYMBOL_GPL(nvmem_cell_read_u16);

/**
 * nvmem_cell_read_u32() - Read a cell value as an u32
 *
 * @dev: Device that requests the nvmem cell.
 * @cell_id: Name of nvmem cell to read.
 * @val: pointer to output value.
 *
 * Return: 0 on success or negative errno.
 */
int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val)
{
	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
}
EXPORT_SYMBOL_GPL(nvmem_cell_read_u32);

/**
 * nvmem_cell_read_u64() - Read a cell value as an u64
 *
 * @dev: Device that requests the nvmem cell.
 * @cell_id: Name of nvmem cell to read.
 * @val: pointer to output value.
 *
 * Return: 0 on success or negative errno.
 */
int nvmem_cell_read_u64(struct device *dev, const char *cell_id, u64 *val)
{
	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
}
EXPORT_SYMBOL_GPL(nvmem_cell_read_u64);

/**
 * nvmem_device_cell_read() - Read a given nvmem device and cell
 *
 * @nvmem: nvmem device to read from.
 * @info: nvmem cell info to be read.
 * @buf: buffer pointer which will be populated on successful read.
 *
 * Return: length of successful bytes read on success and negative
 * error code on error.
 */
ssize_t nvmem_device_cell_read(struct nvmem_device *nvmem,
			   struct nvmem_cell_info *info, void *buf)
{
	struct nvmem_cell cell;
	int rc;
	ssize_t len;

	if (!nvmem)
		return -EINVAL;

	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
	if (rc)
		return rc;

	rc = __nvmem_cell_read(nvmem, &cell, buf, &len);
	if (rc)
		return rc;

	return len;
}
EXPORT_SYMBOL_GPL(nvmem_device_cell_read);

/**
 * nvmem_device_cell_write() - Write cell to a given nvmem device
 *
 * @nvmem: nvmem device to be written to.
 * @info: nvmem cell info to be written.
 * @buf: buffer to be written to cell.
 *
 * Return: length of bytes written or negative error code on failure.
 */
int nvmem_device_cell_write(struct nvmem_device *nvmem,
			    struct nvmem_cell_info *info, void *buf)
{
	struct nvmem_cell cell;
	int rc;

	if (!nvmem)
		return -EINVAL;

	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
	if (rc)
		return rc;

	return nvmem_cell_write(&cell, buf, cell.bytes);
}
EXPORT_SYMBOL_GPL(nvmem_device_cell_write);

/**
 * nvmem_device_read() - Read from a given nvmem device
 *
 * @nvmem: nvmem device to read from.
 * @offset: offset in nvmem device.
 * @bytes: number of bytes to read.
 * @buf: buffer pointer which will be populated on successful read.
 *
 * Return: length of successful bytes read on success and negative
 * error code on error.
 */
int nvmem_device_read(struct nvmem_device *nvmem,
		      unsigned int offset,
		      size_t bytes, void *buf)
{
	int rc;

	if (!nvmem)
		return -EINVAL;

	rc = nvmem_reg_read(nvmem, offset, buf, bytes);

	if (rc)
		return rc;

	return bytes;
}
EXPORT_SYMBOL_GPL(nvmem_device_read);

/**
 * nvmem_device_write() - Write cell to a given nvmem device
 *
 * @nvmem: nvmem device to be written to.
 * @offset: offset in nvmem device.
 * @bytes: number of bytes to write.
 * @buf: buffer to be written.
 *
 * Return: length of bytes written or negative error code on failure.
 */
int nvmem_device_write(struct nvmem_device *nvmem,
		       unsigned int offset,
		       size_t bytes, void *buf)
{
	int rc;

	if (!nvmem)
		return -EINVAL;

	rc = nvmem_reg_write(nvmem, offset, buf, bytes);

	if (rc)
		return rc;


	return bytes;
}
EXPORT_SYMBOL_GPL(nvmem_device_write);

/**
 * nvmem_add_cell_table() - register a table of cell info entries
 *
 * @table: table of cell info entries
 */
void nvmem_add_cell_table(struct nvmem_cell_table *table)
{
	mutex_lock(&nvmem_cell_mutex);
	list_add_tail(&table->node, &nvmem_cell_tables);
	mutex_unlock(&nvmem_cell_mutex);
}
EXPORT_SYMBOL_GPL(nvmem_add_cell_table);

/**
 * nvmem_del_cell_table() - remove a previously registered cell info table
 *
 * @table: table of cell info entries
 */
void nvmem_del_cell_table(struct nvmem_cell_table *table)
{
	mutex_lock(&nvmem_cell_mutex);
	list_del(&table->node);
	mutex_unlock(&nvmem_cell_mutex);
}
EXPORT_SYMBOL_GPL(nvmem_del_cell_table);

/**
 * nvmem_add_cell_lookups() - register a list of cell lookup entries
 *
 * @entries: array of cell lookup entries
 * @nentries: number of cell lookup entries in the array
 */
void nvmem_add_cell_lookups(struct nvmem_cell_lookup *entries, size_t nentries)
{
	int i;

	mutex_lock(&nvmem_lookup_mutex);
	for (i = 0; i < nentries; i++)
		list_add_tail(&entries[i].node, &nvmem_lookup_list);
	mutex_unlock(&nvmem_lookup_mutex);
}
EXPORT_SYMBOL_GPL(nvmem_add_cell_lookups);

/**
 * nvmem_del_cell_lookups() - remove a list of previously added cell lookup
 *                            entries
 *
 * @entries: array of cell lookup entries
 * @nentries: number of cell lookup entries in the array
 */
void nvmem_del_cell_lookups(struct nvmem_cell_lookup *entries, size_t nentries)
{
	int i;

	mutex_lock(&nvmem_lookup_mutex);
	for (i = 0; i < nentries; i++)
		list_del(&entries[i].node);
	mutex_unlock(&nvmem_lookup_mutex);
}
EXPORT_SYMBOL_GPL(nvmem_del_cell_lookups);

/**
 * nvmem_dev_name() - Get the name of a given nvmem device.
 *
 * @nvmem: nvmem device.
 *
 * Return: name of the nvmem device.
 */
const char *nvmem_dev_name(struct nvmem_device *nvmem)
{
	return dev_name(&nvmem->dev);
}
EXPORT_SYMBOL_GPL(nvmem_dev_name);

static int __init nvmem_init(void)
{
	return bus_register(&nvmem_bus_type);
}

static void __exit nvmem_exit(void)
{
	bus_unregister(&nvmem_bus_type);
}

subsys_initcall(nvmem_init);
module_exit(nvmem_exit);

MODULE_AUTHOR("Srinivas Kandagatla <srinivas.kandagatla@linaro.org");
MODULE_AUTHOR("Maxime Ripard <maxime.ripard@free-electrons.com");
MODULE_DESCRIPTION("nvmem Driver Core");
MODULE_LICENSE("GPL v2");