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
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 = CONFIGURATION_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
266static struct workqueue_struct *atmel_wq;
267
268void atmel_i2c_enqueue(struct atmel_i2c_work_data *work_data,
269		       void (*cbk)(struct atmel_i2c_work_data *work_data,
270				   void *areq, int status),
271		       void *areq)
272{
273	work_data->cbk = (void *)cbk;
274	work_data->areq = areq;
275
276	INIT_WORK(&work_data->work, atmel_i2c_work_handler);
277	queue_work(atmel_wq, &work_data->work);
278}
279EXPORT_SYMBOL(atmel_i2c_enqueue);
280
281void atmel_i2c_flush_queue(void)
282{
283	flush_workqueue(atmel_wq);
284}
285EXPORT_SYMBOL(atmel_i2c_flush_queue);
286
287static inline size_t atmel_i2c_wake_token_sz(u32 bus_clk_rate)
288{
289	u32 no_of_bits = DIV_ROUND_UP(TWLO_USEC * bus_clk_rate, USEC_PER_SEC);
290
291	/* return the size of the wake_token in bytes */
292	return DIV_ROUND_UP(no_of_bits, 8);
293}
294
295static int device_sanity_check(struct i2c_client *client)
296{
297	struct atmel_i2c_cmd *cmd;
298	int ret;
299
300	cmd = kmalloc(sizeof(*cmd), GFP_KERNEL);
301	if (!cmd)
302		return -ENOMEM;
303
304	atmel_i2c_init_read_cmd(cmd);
305
306	ret = atmel_i2c_send_receive(client, cmd);
307	if (ret)
308		goto free_cmd;
309
310	/*
311	 * It is vital that the Configuration, Data and OTP zones be locked
312	 * prior to release into the field of the system containing the device.
313	 * Failure to lock these zones may permit modification of any secret
314	 * keys and may lead to other security problems.
315	 */
316	if (cmd->data[LOCK_CONFIG_IDX] || cmd->data[LOCK_VALUE_IDX]) {
317		dev_err(&client->dev, "Configuration or Data and OTP zones are unlocked!\n");
318		ret = -ENOTSUPP;
319	}
320
321	/* fall through */
322free_cmd:
323	kfree(cmd);
324	return ret;
325}
326
327int atmel_i2c_probe(struct i2c_client *client)
328{
329	struct atmel_i2c_client_priv *i2c_priv;
330	struct device *dev = &client->dev;
331	int ret;
332	u32 bus_clk_rate;
333
334	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
335		dev_err(dev, "I2C_FUNC_I2C not supported\n");
336		return -ENODEV;
337	}
338
339	bus_clk_rate = i2c_acpi_find_bus_speed(&client->adapter->dev);
340	if (!bus_clk_rate) {
341		ret = device_property_read_u32(&client->adapter->dev,
342					       "clock-frequency", &bus_clk_rate);
343		if (ret) {
344			dev_err(dev, "failed to read clock-frequency property\n");
345			return ret;
346		}
347	}
348
349	if (bus_clk_rate > 1000000L) {
350		dev_err(dev, "%u exceeds maximum supported clock frequency (1MHz)\n",
351			bus_clk_rate);
352		return -EINVAL;
353	}
354
355	i2c_priv = devm_kmalloc(dev, sizeof(*i2c_priv), GFP_KERNEL);
356	if (!i2c_priv)
357		return -ENOMEM;
358
359	i2c_priv->client = client;
360	mutex_init(&i2c_priv->lock);
361
362	/*
363	 * WAKE_TOKEN_MAX_SIZE was calculated for the maximum bus_clk_rate -
364	 * 1MHz. The previous bus_clk_rate check ensures us that wake_token_sz
365	 * will always be smaller than or equal to WAKE_TOKEN_MAX_SIZE.
366	 */
367	i2c_priv->wake_token_sz = atmel_i2c_wake_token_sz(bus_clk_rate);
368
369	memset(i2c_priv->wake_token, 0, sizeof(i2c_priv->wake_token));
370
371	atomic_set(&i2c_priv->tfm_count, 0);
372
373	i2c_set_clientdata(client, i2c_priv);
374
375	return device_sanity_check(client);
376}
377EXPORT_SYMBOL(atmel_i2c_probe);
378
379static int __init atmel_i2c_init(void)
380{
381	atmel_wq = alloc_workqueue("atmel_wq", 0, 0);
382	return atmel_wq ? 0 : -ENOMEM;
383}
384
385static void __exit atmel_i2c_exit(void)
386{
387	destroy_workqueue(atmel_wq);
388}
389
390module_init(atmel_i2c_init);
391module_exit(atmel_i2c_exit);
392
393MODULE_AUTHOR("Tudor Ambarus");
394MODULE_DESCRIPTION("Microchip / Atmel ECC (I2C) driver");
395MODULE_LICENSE("GPL v2");
396