/*
   * nvmem framework core.
   *
   * Copyright (C) 2015 Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
   * Copyright (C) 2013 Maxime Ripard <maxime.ripard@free-electrons.com>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 and
   * only version 2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #include <linux/device.h>
  #include <linux/export.h>
  #include <linux/fs.h>
  #include <linux/idr.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/nvmem-consumer.h>
  #include <linux/nvmem-provider.h>
  #include <linux/of.h>
  #include <linux/regmap.h>
  #include <linux/slab.h>
  
  struct nvmem_device {
  	const char		*name;
  	struct regmap		*regmap;
  	struct module		*owner;
  	struct device		dev;
  	int			stride;
  	int			word_size;
  	int			ncells;
  	int			id;
  	int			users;
  	size_t			size;
  	bool			read_only;
  };
  
  struct nvmem_cell {
  	const char		*name;
  	int			offset;
  	int			bytes;
  	int			bit_offset;
  	int			nbits;
  	struct nvmem_device	*nvmem;
  	struct list_head	node;
  };
  
  static DEFINE_MUTEX(nvmem_mutex);
  static DEFINE_IDA(nvmem_ida);
  
  static LIST_HEAD(nvmem_cells);
  static DEFINE_MUTEX(nvmem_cells_mutex);
  
  #define to_nvmem_device(d) container_of(d, struct nvmem_device, dev)
  
  static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
  				    struct bin_attribute *attr,
  				    char *buf, loff_t pos, size_t count)
  {
  	struct device *dev = container_of(kobj, struct device, kobj);
  	struct nvmem_device *nvmem = to_nvmem_device(dev);
  	int rc;
  
  	/* Stop the user from reading */
  	if (pos >= nvmem->size)
  		return 0;
  
  	if (pos + count > nvmem->size)
  		count = nvmem->size - pos;
  
  	count = round_down(count, nvmem->word_size);
  
  	rc = regmap_raw_read(nvmem->regmap, pos, buf, count);
  
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  	return count;
  }
  
  static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
  				     struct bin_attribute *attr,
  				     char *buf, loff_t pos, size_t count)
  {
  	struct device *dev = container_of(kobj, struct device, kobj);
  	struct nvmem_device *nvmem = to_nvmem_device(dev);
  	int rc;
  
  	/* Stop the user from writing */
  	if (pos >= nvmem->size)
  		return 0;
  
  	if (pos + count > nvmem->size)
  		count = nvmem->size - pos;
  
  	count = round_down(count, nvmem->word_size);
  
  	rc = regmap_raw_write(nvmem->regmap, pos, buf, count);
  
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  	return count;
  }
  
  /* default read/write permissions */
  static struct bin_attribute bin_attr_rw_nvmem = {
  	.attr	= {
  		.name	= "nvmem",
  		.mode	= S_IWUSR | S_IRUGO,
  	},
  	.read	= bin_attr_nvmem_read,
  	.write	= bin_attr_nvmem_write,
  };
  
  static struct bin_attribute *nvmem_bin_rw_attributes[] = {
  	&bin_attr_rw_nvmem,
  	NULL,
  };
  
  static const struct attribute_group nvmem_bin_rw_group = {
  	.bin_attrs	= nvmem_bin_rw_attributes,
  };
  
  static const struct attribute_group *nvmem_rw_dev_groups[] = {
  	&nvmem_bin_rw_group,
  	NULL,
  };
  
  /* read only permission */
  static struct bin_attribute bin_attr_ro_nvmem = {
  	.attr	= {
  		.name	= "nvmem",
  		.mode	= S_IRUGO,
  	},
  	.read	= bin_attr_nvmem_read,
  };
  
  static struct bin_attribute *nvmem_bin_ro_attributes[] = {
  	&bin_attr_ro_nvmem,
  	NULL,
  };
  
  static const struct attribute_group nvmem_bin_ro_group = {
  	.bin_attrs	= nvmem_bin_ro_attributes,
  };
  
  static const struct attribute_group *nvmem_ro_dev_groups[] = {
  	&nvmem_bin_ro_group,
  	NULL,
  };
  
  static void nvmem_release(struct device *dev)
  {
  	struct nvmem_device *nvmem = to_nvmem_device(dev);
  
  	ida_simple_remove(&nvmem_ida, nvmem->id);
  	kfree(nvmem);
  }
  
  static const struct device_type nvmem_provider_type = {
  	.release	= nvmem_release,
  };
  
  static struct bus_type nvmem_bus_type = {
  	.name		= "nvmem",
  };
  
  static int of_nvmem_match(struct device *dev, void *nvmem_np)
  {
  	return dev->of_node == nvmem_np;
  }
  
  static struct nvmem_device *of_nvmem_find(struct device_node *nvmem_np)
  {
  	struct device *d;
  
  	if (!nvmem_np)
  		return NULL;
  
  	d = bus_find_device(&nvmem_bus_type, NULL, nvmem_np, of_nvmem_match);
  
  	if (!d)
  		return NULL;
  
  	return to_nvmem_device(d);
  }
  
  static struct nvmem_cell *nvmem_find_cell(const char *cell_id)
  {
  	struct nvmem_cell *p;
  
  	list_for_each_entry(p, &nvmem_cells, node)
  		if (p && !strcmp(p->name, cell_id))
  			return p;
  
  	return NULL;
  }
  
  static void nvmem_cell_drop(struct nvmem_cell *cell)
  {
  	mutex_lock(&nvmem_cells_mutex);
  	list_del(&cell->node);
  	mutex_unlock(&nvmem_cells_mutex);
  	kfree(cell);
  }
  
  static void nvmem_device_remove_all_cells(const struct nvmem_device *nvmem)
  {
  	struct nvmem_cell *cell;
  	struct list_head *p, *n;
  
  	list_for_each_safe(p, n, &nvmem_cells) {
  		cell = list_entry(p, struct nvmem_cell, node);
  		if (cell->nvmem == nvmem)
  			nvmem_cell_drop(cell);
  	}
  }
  
  static void nvmem_cell_add(struct nvmem_cell *cell)
  {
  	mutex_lock(&nvmem_cells_mutex);
  	list_add_tail(&cell->node, &nvmem_cells);
  	mutex_unlock(&nvmem_cells_mutex);
  }
  
  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 = info->name;
  
  	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
  ",
  			cell->name, nvmem->stride);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int nvmem_add_cells(struct nvmem_device *nvmem,
  			   const struct nvmem_config *cfg)
  {
  	struct nvmem_cell **cells;
  	const struct nvmem_cell_info *info = cfg->cells;
  	int i, rval;
  
  	cells = kcalloc(cfg->ncells, sizeof(*cells), GFP_KERNEL);
  	if (!cells)
  		return -ENOMEM;
  
  	for (i = 0; i < cfg->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 (IS_ERR_VALUE(rval)) {
  			kfree(cells[i]);
  			goto err;
  		}
  
  		nvmem_cell_add(cells[i]);
  	}
  
  	nvmem->ncells = cfg->ncells;
  	/* remove tmp array */
  	kfree(cells);
  
  	return 0;
  err:
  	while (--i)
  		nvmem_cell_drop(cells[i]);
  
  	return rval;
  }
  
  /**
   * 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;
  	struct device_node *np;
  	struct regmap *rm;
  	int rval;
  
  	if (!config->dev)
  		return ERR_PTR(-EINVAL);
  
  	rm = dev_get_regmap(config->dev, NULL);
  	if (!rm) {
  		dev_err(config->dev, "Regmap not found
  ");
  		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);
  	}
  
  	nvmem->id = rval;
  	nvmem->regmap = rm;
  	nvmem->owner = config->owner;
  	nvmem->stride = regmap_get_reg_stride(rm);
  	nvmem->word_size = regmap_get_val_bytes(rm);
  	nvmem->size = regmap_get_max_register(rm) + nvmem->stride;
  	nvmem->dev.type = &nvmem_provider_type;
  	nvmem->dev.bus = &nvmem_bus_type;
  	nvmem->dev.parent = config->dev;
  	np = config->dev->of_node;
  	nvmem->dev.of_node = np;
  	dev_set_name(&nvmem->dev, "%s%d",
  		     config->name ? : "nvmem", config->id);
  
  	nvmem->read_only = of_property_read_bool(np, "read-only") |
  			   config->read_only;
  
  	nvmem->dev.groups = nvmem->read_only ? nvmem_ro_dev_groups :
  					       nvmem_rw_dev_groups;
  
  	device_initialize(&nvmem->dev);
  
  	dev_dbg(&nvmem->dev, "Registering nvmem device %s
  ", config->name);
  
  	rval = device_add(&nvmem->dev);
  	if (rval) {
  		ida_simple_remove(&nvmem_ida, nvmem->id);
  		kfree(nvmem);
  		return ERR_PTR(rval);
  	}
  
  	if (config->cells)
  		nvmem_add_cells(nvmem, config);
  
  	return nvmem;
  }
  EXPORT_SYMBOL_GPL(nvmem_register);
  
  /**
   * nvmem_unregister() - Unregister previously registered nvmem device
   *
   * @nvmem: Pointer to previously registered nvmem device.
   *
   * Return: Will be an negative on error or a zero on success.
   */
  int nvmem_unregister(struct nvmem_device *nvmem)
  {
  	mutex_lock(&nvmem_mutex);
  	if (nvmem->users) {
  		mutex_unlock(&nvmem_mutex);
  		return -EBUSY;
  	}
  	mutex_unlock(&nvmem_mutex);
  
  	nvmem_device_remove_all_cells(nvmem);
  	device_del(&nvmem->dev);
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(nvmem_unregister);
  
  static struct nvmem_device *__nvmem_device_get(struct device_node *np,
  					       struct nvmem_cell **cellp,
  					       const char *cell_id)
  {
  	struct nvmem_device *nvmem = NULL;
  
  	mutex_lock(&nvmem_mutex);
  
  	if (np) {
  		nvmem = of_nvmem_find(np);
  		if (!nvmem) {
  			mutex_unlock(&nvmem_mutex);
  			return ERR_PTR(-EPROBE_DEFER);
  		}
  	} else {
  		struct nvmem_cell *cell = nvmem_find_cell(cell_id);
  
  		if (cell) {
  			nvmem = cell->nvmem;
  			*cellp = cell;
  		}
  
  		if (!nvmem) {
  			mutex_unlock(&nvmem_mutex);
  			return ERR_PTR(-ENOENT);
  		}
  	}
  
  	nvmem->users++;
  	mutex_unlock(&nvmem_mutex);
  
  	if (!try_module_get(nvmem->owner)) {
  		dev_err(&nvmem->dev,
  			"could not increase module refcount for cell %s
  ",
  			nvmem->name);
  
  		mutex_lock(&nvmem_mutex);
  		nvmem->users--;
  		mutex_unlock(&nvmem_mutex);
  
  		return ERR_PTR(-EINVAL);
  	}
  
  	return nvmem;
  }
  
  static void __nvmem_device_put(struct nvmem_device *nvmem)
  {
  	module_put(nvmem->owner);
  	mutex_lock(&nvmem_mutex);
  	nvmem->users--;
  	mutex_unlock(&nvmem_mutex);
  }
  
  static int nvmem_match(struct device *dev, void *data)
  {
  	return !strcmp(dev_name(dev), data);
  }
  
  static struct nvmem_device *nvmem_find(const char *name)
  {
  	struct device *d;
  
  	d = bus_find_device(&nvmem_bus_type, NULL, (void *)name, nvmem_match);
  
  	if (!d)
  		return NULL;
  
  	return to_nvmem_device(d);
  }
  
  #if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)
  /**
   * of_nvmem_device_get() - Get nvmem device from a given id
   *
   * @dev node: 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;
  
  	index = of_property_match_string(np, "nvmem-names", id);
  
  	nvmem_np = of_parse_phandle(np, "nvmem", index);
  	if (!nvmem_np)
  		return ERR_PTR(-EINVAL);
  
  	return __nvmem_device_get(nvmem_np, NULL, NULL);
  }
  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
   * @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 *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_find(dev_name);
  }
  EXPORT_SYMBOL_GPL(nvmem_device_get);
  
  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
   *
   * @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 node: Device tree node that uses the nvmem cell
   * @id: nvmem name in nvmems property.
   *
   * 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_list(const char *cell_id)
  {
  	struct nvmem_cell *cell = NULL;
  	struct nvmem_device *nvmem;
  
  	nvmem = __nvmem_device_get(NULL, &cell, cell_id);
  	if (IS_ERR(nvmem))
  		return ERR_CAST(nvmem);
  
  	return cell;
  }
  
  #if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)
  /**
   * of_nvmem_cell_get() - Get a nvmem cell from given device node and cell id
   *
   * @dev node: Device tree node that uses the nvmem cell
   * @id: nvmem cell name from 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 *name)
  {
  	struct device_node *cell_np, *nvmem_np;
  	struct nvmem_cell *cell;
  	struct nvmem_device *nvmem;
  	const __be32 *addr;
  	int rval, len, index;
  
  	index = of_property_match_string(np, "nvmem-cell-names", name);
  
  	cell_np = of_parse_phandle(np, "nvmem-cells", index);
  	if (!cell_np)
  		return ERR_PTR(-EINVAL);
  
  	nvmem_np = of_get_next_parent(cell_np);
  	if (!nvmem_np)
  		return ERR_PTR(-EINVAL);
  
  	nvmem = __nvmem_device_get(nvmem_np, NULL, NULL);
  	if (IS_ERR(nvmem))
  		return ERR_CAST(nvmem);
  
  	addr = of_get_property(cell_np, "reg", &len);
  	if (!addr || (len < 2 * sizeof(u32))) {
  		dev_err(&nvmem->dev, "nvmem: invalid reg on %s
  ",
  			cell_np->full_name);
  		rval  = -EINVAL;
  		goto err_mem;
  	}
  
  	cell = kzalloc(sizeof(*cell), GFP_KERNEL);
  	if (!cell) {
  		rval = -ENOMEM;
  		goto err_mem;
  	}
  
  	cell->nvmem = nvmem;
  	cell->offset = be32_to_cpup(addr++);
  	cell->bytes = be32_to_cpup(addr);
  	cell->name = cell_np->name;
  
  	addr = of_get_property(cell_np, "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(&nvmem->dev,
  				"cell %s unaligned to nvmem stride %d
  ",
  				cell->name, nvmem->stride);
  		rval  = -EINVAL;
  		goto err_sanity;
  	}
  
  	nvmem_cell_add(cell);
  
  	return cell;
  
  err_sanity:
  	kfree(cell);
  
  err_mem:
  	__nvmem_device_put(nvmem);
  
  	return ERR_PTR(rval);
  }
  EXPORT_SYMBOL_GPL(of_nvmem_cell_get);
  #endif
  
  /**
   * nvmem_cell_get() - Get nvmem cell of device form a given cell name
   *
   * @dev node: Device tree node that uses the nvmem cell
   * @id: nvmem cell name 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
   * nvmem_cell_put().
   */
  struct nvmem_cell *nvmem_cell_get(struct device *dev, const char *cell_id)
  {
  	struct nvmem_cell *cell;
  
  	if (dev->of_node) { /* try dt first */
  		cell = of_nvmem_cell_get(dev->of_node, cell_id);
  		if (!IS_ERR(cell) || PTR_ERR(cell) == -EPROBE_DEFER)
  			return cell;
  	}
  
  	return nvmem_cell_get_from_list(cell_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 node: Device tree node that uses the nvmem cell
   * @id: nvmem id in nvmem-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
   * 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.
   *
   * @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);
  	nvmem_cell_drop(cell);
  }
  EXPORT_SYMBOL_GPL(nvmem_cell_put);
  
  static inline void nvmem_shift_read_buffer_in_place(struct nvmem_cell *cell,
  						    void *buf)
  {
  	u8 *p, *b;
  	int i, 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;
  		}
  
  		/* result fits in less bytes */
  		if (cell->bytes != DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE))
  			*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 = regmap_raw_read(nvmem->regmap, cell->offset, buf, cell->bytes);
  
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  	/* shift bits in-place */
  	if (cell->bit_offset || cell->nbits)
  		nvmem_shift_read_buffer_in_place(cell, buf);
  
  	*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.
   *
   * Return: ERR_PTR() on error or a valid pointer to a char * 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 || !nvmem->regmap)
  		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 (IS_ERR_VALUE(rc)) {
  		kfree(buf);
  		return ERR_PTR(rc);
  	}
  
  	return buf;
  }
  EXPORT_SYMBOL_GPL(nvmem_cell_read);
  
  static inline 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 = regmap_raw_read(nvmem->regmap, cell->offset, &v, 1);
  		*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 = regmap_raw_read(nvmem->regmap,
  				    cell->offset + cell->bytes - 1, &v, 1);
  		*p |= GENMASK(7, (nbits + bit_offset) % BITS_PER_BYTE) & v;
  
  	}
  
  	return buf;
  }
  
  /**
   * 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->regmap || 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 = regmap_raw_write(nvmem->regmap, cell->offset, buf, cell->bytes);
  
  	/* free the tmp buffer */
  	if (cell->bit_offset || cell->nbits)
  		kfree(buf);
  
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  	return len;
  }
  EXPORT_SYMBOL_GPL(nvmem_cell_write);
  
  /**
   * 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 || !nvmem->regmap)
  		return -EINVAL;
  
  	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  	rc = __nvmem_cell_read(nvmem, &cell, buf, &len);
  	if (IS_ERR_VALUE(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 || !nvmem->regmap)
  		return -EINVAL;
  
  	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
  	if (IS_ERR_VALUE(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 || !nvmem->regmap)
  		return -EINVAL;
  
  	rc = regmap_raw_read(nvmem->regmap, offset, buf, bytes);
  
  	if (IS_ERR_VALUE(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 || !nvmem->regmap)
  		return -EINVAL;
  
  	rc = regmap_raw_write(nvmem->regmap, offset, buf, bytes);
  
  	if (IS_ERR_VALUE(rc))
  		return rc;
  
  
  	return bytes;
  }
  EXPORT_SYMBOL_GPL(nvmem_device_write);
  
  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");