linux/drivers/crypto/atmel-i2c.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Microchip / Atmel ECC (I2C) driver.
   4 *
   5 * Copyright (c) 2017, Microchip Technology Inc.
   6 * Author: Tudor Ambarus <tudor.ambarus@microchip.com>
   7 */
   8
   9#include <linux/bitrev.h>
  10#include <linux/crc16.h>
  11#include <linux/delay.h>
  12#include <linux/device.h>
  13#include <linux/err.h>
  14#include <linux/errno.h>
  15#include <linux/i2c.h>
  16#include <linux/init.h>
  17#include <linux/kernel.h>
  18#include <linux/module.h>
  19#include <linux/scatterlist.h>
  20#include <linux/slab.h>
  21#include <linux/workqueue.h>
  22#include "atmel-i2c.h"
  23
  24static const struct {
  25        u8 value;
  26        const char *error_text;
  27} error_list[] = {
  28        { 0x01, "CheckMac or Verify miscompare" },
  29        { 0x03, "Parse Error" },
  30        { 0x05, "ECC Fault" },
  31        { 0x0F, "Execution Error" },
  32        { 0xEE, "Watchdog about to expire" },
  33        { 0xFF, "CRC or other communication error" },
  34};
  35
  36/**
  37 * atmel_i2c_checksum() - Generate 16-bit CRC as required by ATMEL ECC.
  38 * CRC16 verification of the count, opcode, param1, param2 and data bytes.
  39 * The checksum is saved in little-endian format in the least significant
  40 * two bytes of the command. CRC polynomial is 0x8005 and the initial register
  41 * value should be zero.
  42 *
  43 * @cmd : structure used for communicating with the device.
  44 */
  45static void atmel_i2c_checksum(struct atmel_i2c_cmd *cmd)
  46{
  47        u8 *data = &cmd->count;
  48        size_t len = cmd->count - CRC_SIZE;
  49        __le16 *__crc16 = (__le16 *)(data + len);
  50
  51        *__crc16 = cpu_to_le16(bitrev16(crc16(0, data, len)));
  52}
  53
  54void atmel_i2c_init_read_cmd(struct atmel_i2c_cmd *cmd)
  55{
  56        cmd->word_addr = COMMAND;
  57        cmd->opcode = OPCODE_READ;
  58        /*
  59         * Read the word from Configuration zone that contains the lock bytes
  60         * (UserExtra, Selector, LockValue, LockConfig).
  61         */
  62        cmd->param1 = CONFIG_ZONE;
  63        cmd->param2 = cpu_to_le16(DEVICE_LOCK_ADDR);
  64        cmd->count = READ_COUNT;
  65
  66        atmel_i2c_checksum(cmd);
  67
  68        cmd->msecs = MAX_EXEC_TIME_READ;
  69        cmd->rxsize = READ_RSP_SIZE;
  70}
  71EXPORT_SYMBOL(atmel_i2c_init_read_cmd);
  72
  73void atmel_i2c_init_random_cmd(struct atmel_i2c_cmd *cmd)
  74{
  75        cmd->word_addr = COMMAND;
  76        cmd->opcode = OPCODE_RANDOM;
  77        cmd->param1 = 0;
  78        cmd->param2 = 0;
  79        cmd->count = RANDOM_COUNT;
  80
  81        atmel_i2c_checksum(cmd);
  82
  83        cmd->msecs = MAX_EXEC_TIME_RANDOM;
  84        cmd->rxsize = RANDOM_RSP_SIZE;
  85}
  86EXPORT_SYMBOL(atmel_i2c_init_random_cmd);
  87
  88void atmel_i2c_init_genkey_cmd(struct atmel_i2c_cmd *cmd, u16 keyid)
  89{
  90        cmd->word_addr = COMMAND;
  91        cmd->count = GENKEY_COUNT;
  92        cmd->opcode = OPCODE_GENKEY;
  93        cmd->param1 = GENKEY_MODE_PRIVATE;
  94        /* a random private key will be generated and stored in slot keyID */
  95        cmd->param2 = cpu_to_le16(keyid);
  96
  97        atmel_i2c_checksum(cmd);
  98
  99        cmd->msecs = MAX_EXEC_TIME_GENKEY;
 100        cmd->rxsize = GENKEY_RSP_SIZE;
 101}
 102EXPORT_SYMBOL(atmel_i2c_init_genkey_cmd);
 103
 104int atmel_i2c_init_ecdh_cmd(struct atmel_i2c_cmd *cmd,
 105                            struct scatterlist *pubkey)
 106{
 107        size_t copied;
 108
 109        cmd->word_addr = COMMAND;
 110        cmd->count = ECDH_COUNT;
 111        cmd->opcode = OPCODE_ECDH;
 112        cmd->param1 = ECDH_PREFIX_MODE;
 113        /* private key slot */
 114        cmd->param2 = cpu_to_le16(DATA_SLOT_2);
 115
 116        /*
 117         * The device only supports NIST P256 ECC keys. The public key size will
 118         * always be the same. Use a macro for the key size to avoid unnecessary
 119         * computations.
 120         */
 121        copied = sg_copy_to_buffer(pubkey,
 122                                   sg_nents_for_len(pubkey,
 123                                                    ATMEL_ECC_PUBKEY_SIZE),
 124                                   cmd->data, ATMEL_ECC_PUBKEY_SIZE);
 125        if (copied != ATMEL_ECC_PUBKEY_SIZE)
 126                return -EINVAL;
 127
 128        atmel_i2c_checksum(cmd);
 129
 130        cmd->msecs = MAX_EXEC_TIME_ECDH;
 131        cmd->rxsize = ECDH_RSP_SIZE;
 132
 133        return 0;
 134}
 135EXPORT_SYMBOL(atmel_i2c_init_ecdh_cmd);
 136
 137/*
 138 * After wake and after execution of a command, there will be error, status, or
 139 * result bytes in the device's output register that can be retrieved by the
 140 * system. When the length of that group is four bytes, the codes returned are
 141 * detailed in error_list.
 142 */
 143static int atmel_i2c_status(struct device *dev, u8 *status)
 144{
 145        size_t err_list_len = ARRAY_SIZE(error_list);
 146        int i;
 147        u8 err_id = status[1];
 148
 149        if (*status != STATUS_SIZE)
 150                return 0;
 151
 152        if (err_id == STATUS_WAKE_SUCCESSFUL || err_id == STATUS_NOERR)
 153                return 0;
 154
 155        for (i = 0; i < err_list_len; i++)
 156                if (error_list[i].value == err_id)
 157                        break;
 158
 159        /* if err_id is not in the error_list then ignore it */
 160        if (i != err_list_len) {
 161                dev_err(dev, "%02x: %s:\n", err_id, error_list[i].error_text);
 162                return err_id;
 163        }
 164
 165        return 0;
 166}
 167
 168static int atmel_i2c_wakeup(struct i2c_client *client)
 169{
 170        struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
 171        u8 status[STATUS_RSP_SIZE];
 172        int ret;
 173
 174        /*
 175         * The device ignores any levels or transitions on the SCL pin when the
 176         * device is idle, asleep or during waking up. Don't check for error
 177         * when waking up the device.
 178         */
 179        i2c_transfer_buffer_flags(client, i2c_priv->wake_token,
 180                                i2c_priv->wake_token_sz, I2C_M_IGNORE_NAK);
 181
 182        /*
 183         * Wait to wake the device. Typical execution times for ecdh and genkey
 184         * are around tens of milliseconds. Delta is chosen to 50 microseconds.
 185         */
 186        usleep_range(TWHI_MIN, TWHI_MAX);
 187
 188        ret = i2c_master_recv(client, status, STATUS_SIZE);
 189        if (ret < 0)
 190                return ret;
 191
 192        return atmel_i2c_status(&client->dev, status);
 193}
 194
 195static int atmel_i2c_sleep(struct i2c_client *client)
 196{
 197        u8 sleep = SLEEP_TOKEN;
 198
 199        return i2c_master_send(client, &sleep, 1);
 200}
 201
 202/*
 203 * atmel_i2c_send_receive() - send a command to the device and receive its
 204 *                            response.
 205 * @client: i2c client device
 206 * @cmd   : structure used to communicate with the device
 207 *
 208 * After the device receives a Wake token, a watchdog counter starts within the
 209 * device. After the watchdog timer expires, the device enters sleep mode
 210 * regardless of whether some I/O transmission or command execution is in
 211 * progress. If a command is attempted when insufficient time remains prior to
 212 * watchdog timer execution, the device will return the watchdog timeout error
 213 * code without attempting to execute the command. There is no way to reset the
 214 * counter other than to put the device into sleep or idle mode and then
 215 * wake it up again.
 216 */
 217int atmel_i2c_send_receive(struct i2c_client *client, struct atmel_i2c_cmd *cmd)
 218{
 219        struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
 220        int ret;
 221
 222        mutex_lock(&i2c_priv->lock);
 223
 224        ret = atmel_i2c_wakeup(client);
 225        if (ret)
 226                goto err;
 227
 228        /* send the command */
 229        ret = i2c_master_send(client, (u8 *)cmd, cmd->count + WORD_ADDR_SIZE);
 230        if (ret < 0)
 231                goto err;
 232
 233        /* delay the appropriate amount of time for command to execute */
 234        msleep(cmd->msecs);
 235
 236        /* receive the response */
 237        ret = i2c_master_recv(client, cmd->data, cmd->rxsize);
 238        if (ret < 0)
 239                goto err;
 240
 241        /* put the device into low-power mode */
 242        ret = atmel_i2c_sleep(client);
 243        if (ret < 0)
 244                goto err;
 245
 246        mutex_unlock(&i2c_priv->lock);
 247        return atmel_i2c_status(&client->dev, cmd->data);
 248err:
 249        mutex_unlock(&i2c_priv->lock);
 250        return ret;
 251}
 252EXPORT_SYMBOL(atmel_i2c_send_receive);
 253
 254static void atmel_i2c_work_handler(struct work_struct *work)
 255{
 256        struct atmel_i2c_work_data *work_data =
 257                        container_of(work, struct atmel_i2c_work_data, work);
 258        struct atmel_i2c_cmd *cmd = &work_data->cmd;
 259        struct i2c_client *client = work_data->client;
 260        int status;
 261
 262        status = atmel_i2c_send_receive(client, cmd);
 263        work_data->cbk(work_data, work_data->areq, status);
 264}
 265
 266void atmel_i2c_enqueue(struct atmel_i2c_work_data *work_data,
 267                       void (*cbk)(struct atmel_i2c_work_data *work_data,
 268                                   void *areq, int status),
 269                       void *areq)
 270{
 271        work_data->cbk = (void *)cbk;
 272        work_data->areq = areq;
 273
 274        INIT_WORK(&work_data->work, atmel_i2c_work_handler);
 275        schedule_work(&work_data->work);
 276}
 277EXPORT_SYMBOL(atmel_i2c_enqueue);
 278
 279static inline size_t atmel_i2c_wake_token_sz(u32 bus_clk_rate)
 280{
 281        u32 no_of_bits = DIV_ROUND_UP(TWLO_USEC * bus_clk_rate, USEC_PER_SEC);
 282
 283        /* return the size of the wake_token in bytes */
 284        return DIV_ROUND_UP(no_of_bits, 8);
 285}
 286
 287static int device_sanity_check(struct i2c_client *client)
 288{
 289        struct atmel_i2c_cmd *cmd;
 290        int ret;
 291
 292        cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
 293        if (!cmd)
 294                return -ENOMEM;
 295
 296        atmel_i2c_init_read_cmd(cmd);
 297
 298        ret = atmel_i2c_send_receive(client, cmd);
 299        if (ret)
 300                goto free_cmd;
 301
 302        /*
 303         * It is vital that the Configuration, Data and OTP zones be locked
 304         * prior to release into the field of the system containing the device.
 305         * Failure to lock these zones may permit modification of any secret
 306         * keys and may lead to other security problems.
 307         */
 308        if (cmd->data[LOCK_CONFIG_IDX] || cmd->data[LOCK_VALUE_IDX]) {
 309                dev_err(&client->dev, "Configuration or Data and OTP zones are unlocked!\n");
 310                ret = -ENOTSUPP;
 311        }
 312
 313        /* fall through */
 314free_cmd:
 315        kfree(cmd);
 316        return ret;
 317}
 318
 319int atmel_i2c_probe(struct i2c_client *client, const struct i2c_device_id *id)
 320{
 321        struct atmel_i2c_client_priv *i2c_priv;
 322        struct device *dev = &client->dev;
 323        int ret;
 324        u32 bus_clk_rate;
 325
 326        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 327                dev_err(dev, "I2C_FUNC_I2C not supported\n");
 328                return -ENODEV;
 329        }
 330
 331        bus_clk_rate = i2c_acpi_find_bus_speed(&client->adapter->dev);
 332        if (!bus_clk_rate) {
 333                ret = device_property_read_u32(&client->adapter->dev,
 334                                               "clock-frequency", &bus_clk_rate);
 335                if (ret) {
 336                        dev_err(dev, "failed to read clock-frequency property\n");
 337                        return ret;
 338                }
 339        }
 340
 341        if (bus_clk_rate > 1000000L) {
 342                dev_err(dev, "%u exceeds maximum supported clock frequency (1MHz)\n",
 343                        bus_clk_rate);
 344                return -EINVAL;
 345        }
 346
 347        i2c_priv = devm_kmalloc(dev, sizeof(*i2c_priv), GFP_KERNEL);
 348        if (!i2c_priv)
 349                return -ENOMEM;
 350
 351        i2c_priv->client = client;
 352        mutex_init(&i2c_priv->lock);
 353
 354        /*
 355         * WAKE_TOKEN_MAX_SIZE was calculated for the maximum bus_clk_rate -
 356         * 1MHz. The previous bus_clk_rate check ensures us that wake_token_sz
 357         * will always be smaller than or equal to WAKE_TOKEN_MAX_SIZE.
 358         */
 359        i2c_priv->wake_token_sz = atmel_i2c_wake_token_sz(bus_clk_rate);
 360
 361        memset(i2c_priv->wake_token, 0, sizeof(i2c_priv->wake_token));
 362
 363        atomic_set(&i2c_priv->tfm_count, 0);
 364
 365        i2c_set_clientdata(client, i2c_priv);
 366
 367        ret = device_sanity_check(client);
 368        if (ret)
 369                return ret;
 370
 371        return 0;
 372}
 373EXPORT_SYMBOL(atmel_i2c_probe);
 374
 375MODULE_AUTHOR("Tudor Ambarus <tudor.ambarus@microchip.com>");
 376MODULE_DESCRIPTION("Microchip / Atmel ECC (I2C) driver");
 377MODULE_LICENSE("GPL v2");
 378