Linux 4.19.133

[linux/fpc-iii.git] / drivers / crypto / atmel-ecc.c

/*
 * Microchip / Atmel ECC (I2C) driver.
 *
 * Copyright (c) 2017, Microchip Technology Inc.
 * Author: Tudor Ambarus <tudor.ambarus@microchip.com>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * 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/bitrev.h>
#include <linux/crc16.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <crypto/internal/kpp.h>
#include <crypto/ecdh.h>
#include <crypto/kpp.h>
#include "atmel-ecc.h"

/* Used for binding tfm objects to i2c clients. */
struct atmel_ecc_driver_data {
        struct list_head i2c_client_list;
        spinlock_t i2c_list_lock;
} ____cacheline_aligned;

static struct atmel_ecc_driver_data driver_data;

/**
 * atmel_ecc_i2c_client_priv - i2c_client private data
 * @client              : pointer to i2c client device
 * @i2c_client_list_node: part of i2c_client_list
 * @lock                : lock for sending i2c commands
 * @wake_token          : wake token array of zeros
 * @wake_token_sz       : size in bytes of the wake_token
 * @tfm_count           : number of active crypto transformations on i2c client
 *
 * Reads and writes from/to the i2c client are sequential. The first byte
 * transmitted to the device is treated as the byte size. Any attempt to send
 * more than this number of bytes will cause the device to not ACK those bytes.
 * After the host writes a single command byte to the input buffer, reads are
 * prohibited until after the device completes command execution. Use a mutex
 * when sending i2c commands.
 */
struct atmel_ecc_i2c_client_priv {
        struct i2c_client *client;
        struct list_head i2c_client_list_node;
        struct mutex lock;
        u8 wake_token[WAKE_TOKEN_MAX_SIZE];
        size_t wake_token_sz;
        atomic_t tfm_count ____cacheline_aligned;
};

/**
 * atmel_ecdh_ctx - transformation context
 * @client     : pointer to i2c client device
 * @fallback   : used for unsupported curves or when user wants to use its own
 *               private key.
 * @public_key : generated when calling set_secret(). It's the responsibility
 *               of the user to not call set_secret() while
 *               generate_public_key() or compute_shared_secret() are in flight.
 * @curve_id   : elliptic curve id
 * @n_sz       : size in bytes of the n prime
 * @do_fallback: true when the device doesn't support the curve or when the user
 *               wants to use its own private key.
 */
struct atmel_ecdh_ctx {
        struct i2c_client *client;
        struct crypto_kpp *fallback;
        const u8 *public_key;
        unsigned int curve_id;
        size_t n_sz;
        bool do_fallback;
};

/**
 * atmel_ecc_work_data - data structure representing the work
 * @ctx : transformation context.
 * @cbk : pointer to a callback function to be invoked upon completion of this
 *        request. This has the form:
 *        callback(struct atmel_ecc_work_data *work_data, void *areq, u8 status)
 *        where:
 *        @work_data: data structure representing the work
 *        @areq     : optional pointer to an argument passed with the original
 *                    request.
 *        @status   : status returned from the i2c client device or i2c error.
 * @areq: optional pointer to a user argument for use at callback time.
 * @work: describes the task to be executed.
 * @cmd : structure used for communicating with the device.
 */
struct atmel_ecc_work_data {
        struct atmel_ecdh_ctx *ctx;
        void (*cbk)(struct atmel_ecc_work_data *work_data, void *areq,
                    int status);
        void *areq;
        struct work_struct work;
        struct atmel_ecc_cmd cmd;
};

static u16 atmel_ecc_crc16(u16 crc, const u8 *buffer, size_t len)
{
        return cpu_to_le16(bitrev16(crc16(crc, buffer, len)));
}

/**
 * atmel_ecc_checksum() - Generate 16-bit CRC as required by ATMEL ECC.
 * CRC16 verification of the count, opcode, param1, param2 and data bytes.
 * The checksum is saved in little-endian format in the least significant
 * two bytes of the command. CRC polynomial is 0x8005 and the initial register
 * value should be zero.
 *
 * @cmd : structure used for communicating with the device.
 */
static void atmel_ecc_checksum(struct atmel_ecc_cmd *cmd)
{
        u8 *data = &cmd->count;
        size_t len = cmd->count - CRC_SIZE;
        u16 *crc16 = (u16 *)(data + len);

        *crc16 = atmel_ecc_crc16(0, data, len);
}

static void atmel_ecc_init_read_cmd(struct atmel_ecc_cmd *cmd)
{
        cmd->word_addr = COMMAND;
        cmd->opcode = OPCODE_READ;
        /*
         * Read the word from Configuration zone that contains the lock bytes
         * (UserExtra, Selector, LockValue, LockConfig).
         */
        cmd->param1 = CONFIG_ZONE;
        cmd->param2 = DEVICE_LOCK_ADDR;
        cmd->count = READ_COUNT;

        atmel_ecc_checksum(cmd);

        cmd->msecs = MAX_EXEC_TIME_READ;
        cmd->rxsize = READ_RSP_SIZE;
}

static void atmel_ecc_init_genkey_cmd(struct atmel_ecc_cmd *cmd, u16 keyid)
{
        cmd->word_addr = COMMAND;
        cmd->count = GENKEY_COUNT;
        cmd->opcode = OPCODE_GENKEY;
        cmd->param1 = GENKEY_MODE_PRIVATE;
        /* a random private key will be generated and stored in slot keyID */
        cmd->param2 = cpu_to_le16(keyid);

        atmel_ecc_checksum(cmd);

        cmd->msecs = MAX_EXEC_TIME_GENKEY;
        cmd->rxsize = GENKEY_RSP_SIZE;
}

static int atmel_ecc_init_ecdh_cmd(struct atmel_ecc_cmd *cmd,
                                   struct scatterlist *pubkey)
{
        size_t copied;

        cmd->word_addr = COMMAND;
        cmd->count = ECDH_COUNT;
        cmd->opcode = OPCODE_ECDH;
        cmd->param1 = ECDH_PREFIX_MODE;
        /* private key slot */
        cmd->param2 = cpu_to_le16(DATA_SLOT_2);

        /*
         * The device only supports NIST P256 ECC keys. The public key size will
         * always be the same. Use a macro for the key size to avoid unnecessary
         * computations.
         */
        copied = sg_copy_to_buffer(pubkey,
                                   sg_nents_for_len(pubkey,
                                                    ATMEL_ECC_PUBKEY_SIZE),
                                   cmd->data, ATMEL_ECC_PUBKEY_SIZE);
        if (copied != ATMEL_ECC_PUBKEY_SIZE)
                return -EINVAL;

        atmel_ecc_checksum(cmd);

        cmd->msecs = MAX_EXEC_TIME_ECDH;
        cmd->rxsize = ECDH_RSP_SIZE;

        return 0;
}

/*
 * After wake and after execution of a command, there will be error, status, or
 * result bytes in the device's output register that can be retrieved by the
 * system. When the length of that group is four bytes, the codes returned are
 * detailed in error_list.
 */
static int atmel_ecc_status(struct device *dev, u8 *status)
{
        size_t err_list_len = ARRAY_SIZE(error_list);
        int i;
        u8 err_id = status[1];

        if (*status != STATUS_SIZE)
                return 0;

        if (err_id == STATUS_WAKE_SUCCESSFUL || err_id == STATUS_NOERR)
                return 0;

        for (i = 0; i < err_list_len; i++)
                if (error_list[i].value == err_id)
                        break;

        /* if err_id is not in the error_list then ignore it */
        if (i != err_list_len) {
                dev_err(dev, "%02x: %s:\n", err_id, error_list[i].error_text);
                return err_id;
        }

        return 0;
}

static int atmel_ecc_wakeup(struct i2c_client *client)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
        u8 status[STATUS_RSP_SIZE];
        int ret;

        /*
         * The device ignores any levels or transitions on the SCL pin when the
         * device is idle, asleep or during waking up. Don't check for error
         * when waking up the device.
         */
        i2c_master_send(client, i2c_priv->wake_token, i2c_priv->wake_token_sz);

        /*
         * Wait to wake the device. Typical execution times for ecdh and genkey
         * are around tens of milliseconds. Delta is chosen to 50 microseconds.
         */
        usleep_range(TWHI_MIN, TWHI_MAX);

        ret = i2c_master_recv(client, status, STATUS_SIZE);
        if (ret < 0)
                return ret;

        return atmel_ecc_status(&client->dev, status);
}

static int atmel_ecc_sleep(struct i2c_client *client)
{
        u8 sleep = SLEEP_TOKEN;

        return i2c_master_send(client, &sleep, 1);
}

static void atmel_ecdh_done(struct atmel_ecc_work_data *work_data, void *areq,
                            int status)
{
        struct kpp_request *req = areq;
        struct atmel_ecdh_ctx *ctx = work_data->ctx;
        struct atmel_ecc_cmd *cmd = &work_data->cmd;
        size_t copied, n_sz;

        if (status)
                goto free_work_data;

        /* might want less than we've got */
        n_sz = min_t(size_t, ctx->n_sz, req->dst_len);

        /* copy the shared secret */
        copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, n_sz),
                                     &cmd->data[RSP_DATA_IDX], n_sz);
        if (copied != n_sz)
                status = -EINVAL;

        /* fall through */
free_work_data:
        kzfree(work_data);
        kpp_request_complete(req, status);
}

/*
 * atmel_ecc_send_receive() - send a command to the device and receive its
 *                            response.
 * @client: i2c client device
 * @cmd   : structure used to communicate with the device
 *
 * After the device receives a Wake token, a watchdog counter starts within the
 * device. After the watchdog timer expires, the device enters sleep mode
 * regardless of whether some I/O transmission or command execution is in
 * progress. If a command is attempted when insufficient time remains prior to
 * watchdog timer execution, the device will return the watchdog timeout error
 * code without attempting to execute the command. There is no way to reset the
 * counter other than to put the device into sleep or idle mode and then
 * wake it up again.
 */
static int atmel_ecc_send_receive(struct i2c_client *client,
                                  struct atmel_ecc_cmd *cmd)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
        int ret;

        mutex_lock(&i2c_priv->lock);

        ret = atmel_ecc_wakeup(client);
        if (ret)
                goto err;

        /* send the command */
        ret = i2c_master_send(client, (u8 *)cmd, cmd->count + WORD_ADDR_SIZE);
        if (ret < 0)
                goto err;

        /* delay the appropriate amount of time for command to execute */
        msleep(cmd->msecs);

        /* receive the response */
        ret = i2c_master_recv(client, cmd->data, cmd->rxsize);
        if (ret < 0)
                goto err;

        /* put the device into low-power mode */
        ret = atmel_ecc_sleep(client);
        if (ret < 0)
                goto err;

        mutex_unlock(&i2c_priv->lock);
        return atmel_ecc_status(&client->dev, cmd->data);
err:
        mutex_unlock(&i2c_priv->lock);
        return ret;
}

static void atmel_ecc_work_handler(struct work_struct *work)
{
        struct atmel_ecc_work_data *work_data =
                        container_of(work, struct atmel_ecc_work_data, work);
        struct atmel_ecc_cmd *cmd = &work_data->cmd;
        struct i2c_client *client = work_data->ctx->client;
        int status;

        status = atmel_ecc_send_receive(client, cmd);
        work_data->cbk(work_data, work_data->areq, status);
}

static void atmel_ecc_enqueue(struct atmel_ecc_work_data *work_data,
                              void (*cbk)(struct atmel_ecc_work_data *work_data,
                                          void *areq, int status),
                              void *areq)
{
        work_data->cbk = (void *)cbk;
        work_data->areq = areq;

        INIT_WORK(&work_data->work, atmel_ecc_work_handler);
        schedule_work(&work_data->work);
}

static unsigned int atmel_ecdh_supported_curve(unsigned int curve_id)
{
        if (curve_id == ECC_CURVE_NIST_P256)
                return ATMEL_ECC_NIST_P256_N_SIZE;

        return 0;
}

/*
 * A random private key is generated and stored in the device. The device
 * returns the pair public key.
 */
static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
                                 unsigned int len)
{
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
        struct atmel_ecc_cmd *cmd;
        void *public_key;
        struct ecdh params;
        int ret = -ENOMEM;

        /* free the old public key, if any */
        kfree(ctx->public_key);
        /* make sure you don't free the old public key twice */
        ctx->public_key = NULL;

        if (crypto_ecdh_decode_key(buf, len, &params) < 0) {
                dev_err(&ctx->client->dev, "crypto_ecdh_decode_key failed\n");
                return -EINVAL;
        }

        ctx->n_sz = atmel_ecdh_supported_curve(params.curve_id);
        if (!ctx->n_sz || params.key_size) {
                /* fallback to ecdh software implementation */
                ctx->do_fallback = true;
                return crypto_kpp_set_secret(ctx->fallback, buf, len);
        }

        cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
        if (!cmd)
                return -ENOMEM;

        /*
         * The device only supports NIST P256 ECC keys. The public key size will
         * always be the same. Use a macro for the key size to avoid unnecessary
         * computations.
         */
        public_key = kmalloc(ATMEL_ECC_PUBKEY_SIZE, GFP_KERNEL);
        if (!public_key)
                goto free_cmd;

        ctx->do_fallback = false;
        ctx->curve_id = params.curve_id;

        atmel_ecc_init_genkey_cmd(cmd, DATA_SLOT_2);

        ret = atmel_ecc_send_receive(ctx->client, cmd);
        if (ret)
                goto free_public_key;

        /* save the public key */
        memcpy(public_key, &cmd->data[RSP_DATA_IDX], ATMEL_ECC_PUBKEY_SIZE);
        ctx->public_key = public_key;

        kfree(cmd);
        return 0;

free_public_key:
        kfree(public_key);
free_cmd:
        kfree(cmd);
        return ret;
}

static int atmel_ecdh_generate_public_key(struct kpp_request *req)
{
        struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
        size_t copied, nbytes;
        int ret = 0;

        if (ctx->do_fallback) {
                kpp_request_set_tfm(req, ctx->fallback);
                return crypto_kpp_generate_public_key(req);
        }

        /* might want less than we've got */
        nbytes = min_t(size_t, ATMEL_ECC_PUBKEY_SIZE, req->dst_len);

        /* public key was saved at private key generation */
        copied = sg_copy_from_buffer(req->dst,
                                     sg_nents_for_len(req->dst, nbytes),
                                     ctx->public_key, nbytes);
        if (copied != nbytes)
                ret = -EINVAL;

        return ret;
}

static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
{
        struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);
        struct atmel_ecc_work_data *work_data;
        gfp_t gfp;
        int ret;

        if (ctx->do_fallback) {
                kpp_request_set_tfm(req, ctx->fallback);
                return crypto_kpp_compute_shared_secret(req);
        }

        /* must have exactly two points to be on the curve */
        if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
                return -EINVAL;

        gfp = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ? GFP_KERNEL :
                                                             GFP_ATOMIC;

        work_data = kmalloc(sizeof(*work_data), gfp);
        if (!work_data)
                return -ENOMEM;

        work_data->ctx = ctx;

        ret = atmel_ecc_init_ecdh_cmd(&work_data->cmd, req->src);
        if (ret)
                goto free_work_data;

        atmel_ecc_enqueue(work_data, atmel_ecdh_done, req);

        return -EINPROGRESS;

free_work_data:
        kfree(work_data);
        return ret;
}

static struct i2c_client *atmel_ecc_i2c_client_alloc(void)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv, *min_i2c_priv = NULL;
        struct i2c_client *client = ERR_PTR(-ENODEV);
        int min_tfm_cnt = INT_MAX;
        int tfm_cnt;

        spin_lock(&driver_data.i2c_list_lock);

        if (list_empty(&driver_data.i2c_client_list)) {
                spin_unlock(&driver_data.i2c_list_lock);
                return ERR_PTR(-ENODEV);
        }

        list_for_each_entry(i2c_priv, &driver_data.i2c_client_list,
                            i2c_client_list_node) {
                tfm_cnt = atomic_read(&i2c_priv->tfm_count);
                if (tfm_cnt < min_tfm_cnt) {
                        min_tfm_cnt = tfm_cnt;
                        min_i2c_priv = i2c_priv;
                }
                if (!min_tfm_cnt)
                        break;
        }

        if (min_i2c_priv) {
                atomic_inc(&min_i2c_priv->tfm_count);
                client = min_i2c_priv->client;
        }

        spin_unlock(&driver_data.i2c_list_lock);

        return client;
}

static void atmel_ecc_i2c_client_free(struct i2c_client *client)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);

        atomic_dec(&i2c_priv->tfm_count);
}

static int atmel_ecdh_init_tfm(struct crypto_kpp *tfm)
{
        const char *alg = kpp_alg_name(tfm);
        struct crypto_kpp *fallback;
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

        ctx->client = atmel_ecc_i2c_client_alloc();
        if (IS_ERR(ctx->client)) {
                pr_err("tfm - i2c_client binding failed\n");
                return PTR_ERR(ctx->client);
        }

        fallback = crypto_alloc_kpp(alg, 0, CRYPTO_ALG_NEED_FALLBACK);
        if (IS_ERR(fallback)) {
                dev_err(&ctx->client->dev, "Failed to allocate transformation for '%s': %ld\n",
                        alg, PTR_ERR(fallback));
                return PTR_ERR(fallback);
        }

        crypto_kpp_set_flags(fallback, crypto_kpp_get_flags(tfm));
        ctx->fallback = fallback;

        return 0;
}

static void atmel_ecdh_exit_tfm(struct crypto_kpp *tfm)
{
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

        kfree(ctx->public_key);
        crypto_free_kpp(ctx->fallback);
        atmel_ecc_i2c_client_free(ctx->client);
}

static unsigned int atmel_ecdh_max_size(struct crypto_kpp *tfm)
{
        struct atmel_ecdh_ctx *ctx = kpp_tfm_ctx(tfm);

        if (ctx->fallback)
                return crypto_kpp_maxsize(ctx->fallback);

        /*
         * The device only supports NIST P256 ECC keys. The public key size will
         * always be the same. Use a macro for the key size to avoid unnecessary
         * computations.
         */
        return ATMEL_ECC_PUBKEY_SIZE;
}

static struct kpp_alg atmel_ecdh = {
        .set_secret = atmel_ecdh_set_secret,
        .generate_public_key = atmel_ecdh_generate_public_key,
        .compute_shared_secret = atmel_ecdh_compute_shared_secret,
        .init = atmel_ecdh_init_tfm,
        .exit = atmel_ecdh_exit_tfm,
        .max_size = atmel_ecdh_max_size,
        .base = {
                .cra_flags = CRYPTO_ALG_NEED_FALLBACK,
                .cra_name = "ecdh",
                .cra_driver_name = "atmel-ecdh",
                .cra_priority = ATMEL_ECC_PRIORITY,
                .cra_module = THIS_MODULE,
                .cra_ctxsize = sizeof(struct atmel_ecdh_ctx),
        },
};

static inline size_t atmel_ecc_wake_token_sz(u32 bus_clk_rate)
{
        u32 no_of_bits = DIV_ROUND_UP(TWLO_USEC * bus_clk_rate, USEC_PER_SEC);

        /* return the size of the wake_token in bytes */
        return DIV_ROUND_UP(no_of_bits, 8);
}

static int device_sanity_check(struct i2c_client *client)
{
        struct atmel_ecc_cmd *cmd;
        int ret;

        cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
        if (!cmd)
                return -ENOMEM;

        atmel_ecc_init_read_cmd(cmd);

        ret = atmel_ecc_send_receive(client, cmd);
        if (ret)
                goto free_cmd;

        /*
         * It is vital that the Configuration, Data and OTP zones be locked
         * prior to release into the field of the system containing the device.
         * Failure to lock these zones may permit modification of any secret
         * keys and may lead to other security problems.
         */
        if (cmd->data[LOCK_CONFIG_IDX] || cmd->data[LOCK_VALUE_IDX]) {
                dev_err(&client->dev, "Configuration or Data and OTP zones are unlocked!\n");
                ret = -ENOTSUPP;
        }

        /* fall through */
free_cmd:
        kfree(cmd);
        return ret;
}

static int atmel_ecc_probe(struct i2c_client *client,
                           const struct i2c_device_id *id)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv;
        struct device *dev = &client->dev;
        int ret;
        u32 bus_clk_rate;

        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
                dev_err(dev, "I2C_FUNC_I2C not supported\n");
                return -ENODEV;
        }

        ret = of_property_read_u32(client->adapter->dev.of_node,
                                   "clock-frequency", &bus_clk_rate);
        if (ret) {
                dev_err(dev, "of: failed to read clock-frequency property\n");
                return ret;
        }

        if (bus_clk_rate > 1000000L) {
                dev_err(dev, "%d exceeds maximum supported clock frequency (1MHz)\n",
                        bus_clk_rate);
                return -EINVAL;
        }

        i2c_priv = devm_kmalloc(dev, sizeof(*i2c_priv), GFP_KERNEL);
        if (!i2c_priv)
                return -ENOMEM;

        i2c_priv->client = client;
        mutex_init(&i2c_priv->lock);

        /*
         * WAKE_TOKEN_MAX_SIZE was calculated for the maximum bus_clk_rate -
         * 1MHz. The previous bus_clk_rate check ensures us that wake_token_sz
         * will always be smaller than or equal to WAKE_TOKEN_MAX_SIZE.
         */
        i2c_priv->wake_token_sz = atmel_ecc_wake_token_sz(bus_clk_rate);

        memset(i2c_priv->wake_token, 0, sizeof(i2c_priv->wake_token));

        atomic_set(&i2c_priv->tfm_count, 0);

        i2c_set_clientdata(client, i2c_priv);

        ret = device_sanity_check(client);
        if (ret)
                return ret;

        spin_lock(&driver_data.i2c_list_lock);
        list_add_tail(&i2c_priv->i2c_client_list_node,
                      &driver_data.i2c_client_list);
        spin_unlock(&driver_data.i2c_list_lock);

        ret = crypto_register_kpp(&atmel_ecdh);
        if (ret) {
                spin_lock(&driver_data.i2c_list_lock);
                list_del(&i2c_priv->i2c_client_list_node);
                spin_unlock(&driver_data.i2c_list_lock);

                dev_err(dev, "%s alg registration failed\n",
                        atmel_ecdh.base.cra_driver_name);
        } else {
                dev_info(dev, "atmel ecc algorithms registered in /proc/crypto\n");
        }

        return ret;
}

static int atmel_ecc_remove(struct i2c_client *client)
{
        struct atmel_ecc_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);

        /* Return EBUSY if i2c client already allocated. */
        if (atomic_read(&i2c_priv->tfm_count)) {
                dev_err(&client->dev, "Device is busy\n");
                return -EBUSY;
        }

        crypto_unregister_kpp(&atmel_ecdh);

        spin_lock(&driver_data.i2c_list_lock);
        list_del(&i2c_priv->i2c_client_list_node);
        spin_unlock(&driver_data.i2c_list_lock);

        return 0;
}

#ifdef CONFIG_OF
static const struct of_device_id atmel_ecc_dt_ids[] = {
        {
                .compatible = "atmel,atecc508a",
        }, {
                /* sentinel */
        }
};
MODULE_DEVICE_TABLE(of, atmel_ecc_dt_ids);
#endif

static const struct i2c_device_id atmel_ecc_id[] = {
        { "atecc508a", 0 },
        { }
};
MODULE_DEVICE_TABLE(i2c, atmel_ecc_id);

static struct i2c_driver atmel_ecc_driver = {
        .driver = {
                .name   = "atmel-ecc",
                .of_match_table = of_match_ptr(atmel_ecc_dt_ids),
        },
        .probe          = atmel_ecc_probe,
        .remove         = atmel_ecc_remove,
        .id_table       = atmel_ecc_id,
};

static int __init atmel_ecc_init(void)
{
        spin_lock_init(&driver_data.i2c_list_lock);
        INIT_LIST_HEAD(&driver_data.i2c_client_list);
        return i2c_add_driver(&atmel_ecc_driver);
}

static void __exit atmel_ecc_exit(void)
{
        flush_scheduled_work();
        i2c_del_driver(&atmel_ecc_driver);
}

module_init(atmel_ecc_init);
module_exit(atmel_ecc_exit);

MODULE_AUTHOR("Tudor Ambarus <tudor.ambarus@microchip.com>");
MODULE_DESCRIPTION("Microchip / Atmel ECC (I2C) driver");
MODULE_LICENSE("GPL v2");