usb: dwc2: refactor common low-level hw code to platform.c

[linux/fpc-iii.git] / drivers / nvmem / core.c

/*
 * 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\n",
                        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\n");
                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\n", 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\n",
                        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\n",
                        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\n",
                                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->bit_offset)
                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)
                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");