atmel-sha204a.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Microchip / Atmel SHA204A (I2C) driver.
  4 *
  5 * Copyright (c) 2019 Linaro, Ltd. <ard.biesheuvel@linaro.org>
  6 */
  7
  8#include <linux/delay.h>
  9#include <linux/device.h>
 10#include <linux/err.h>
 11#include <linux/errno.h>
 12#include <linux/i2c.h>
 13#include <linux/init.h>
 14#include <linux/kernel.h>
 15#include <linux/module.h>
 16#include <linux/scatterlist.h>
 17#include <linux/slab.h>
 18#include <linux/workqueue.h>
 19#include "atmel-i2c.h"
 20
 21static void atmel_sha204a_rng_done(struct atmel_i2c_work_data *work_data,
 22				   void *areq, int status)
 23{
 24	struct atmel_i2c_client_priv *i2c_priv = work_data->ctx;
 25	struct hwrng *rng = areq;
 26
 27	if (status)
 28		dev_warn_ratelimited(&i2c_priv->client->dev,
 29				     "i2c transaction failed (%d)\n",
 30				     status);
 31
 32	rng->priv = (unsigned long)work_data;
 33	atomic_dec(&i2c_priv->tfm_count);
 34}
 35
 36static int atmel_sha204a_rng_read_nonblocking(struct hwrng *rng, void *data,
 37					      size_t max)
 38{
 39	struct atmel_i2c_client_priv *i2c_priv;
 40	struct atmel_i2c_work_data *work_data;
 41
 42	i2c_priv = container_of(rng, struct atmel_i2c_client_priv, hwrng);
 43
 44	/* keep maximum 1 asynchronous read in flight at any time */
 45	if (!atomic_add_unless(&i2c_priv->tfm_count, 1, 1))
 46		return 0;
 47
 48	if (rng->priv) {
 49		work_data = (struct atmel_i2c_work_data *)rng->priv;
 50		max = min(sizeof(work_data->cmd.data), max);
 51		memcpy(data, &work_data->cmd.data, max);
 52		rng->priv = 0;
 53	} else {
 54		work_data = kmalloc(sizeof(*work_data), GFP_ATOMIC);
 55		if (!work_data) {
 56			atomic_dec(&i2c_priv->tfm_count);
 57			return -ENOMEM;
 58		}
 59		work_data->ctx = i2c_priv;
 60		work_data->client = i2c_priv->client;
 61
 62		max = 0;
 63	}
 64
 65	atmel_i2c_init_random_cmd(&work_data->cmd);
 66	atmel_i2c_enqueue(work_data, atmel_sha204a_rng_done, rng);
 67
 68	return max;
 69}
 70
 71static int atmel_sha204a_rng_read(struct hwrng *rng, void *data, size_t max,
 72				  bool wait)
 73{
 74	struct atmel_i2c_client_priv *i2c_priv;
 75	struct atmel_i2c_cmd cmd;
 76	int ret;
 77
 78	if (!wait)
 79		return atmel_sha204a_rng_read_nonblocking(rng, data, max);
 80
 81	i2c_priv = container_of(rng, struct atmel_i2c_client_priv, hwrng);
 82
 83	atmel_i2c_init_random_cmd(&cmd);
 84
 85	ret = atmel_i2c_send_receive(i2c_priv->client, &cmd);
 86	if (ret)
 87		return ret;
 88
 89	max = min(sizeof(cmd.data), max);
 90	memcpy(data, cmd.data, max);
 91
 92	return max;
 93}
 94
 95static int atmel_sha204a_otp_read(struct i2c_client *client, u16 addr, u8 *otp)
 96{
 97	struct atmel_i2c_cmd cmd;
 98	int ret = -1;
 99
100	if (atmel_i2c_init_read_otp_cmd(&cmd, addr) < 0) {
101		dev_err(&client->dev, "failed, invalid otp address %04X\n",
102			addr);
103		return ret;
104	}
105
106	ret = atmel_i2c_send_receive(client, &cmd);
107
108	if (cmd.data[0] == 0xff) {
109		dev_err(&client->dev, "failed, device not ready\n");
110		return -EINVAL;
111	}
112
113	memcpy(otp, cmd.data+1, 4);
114
115	return ret;
116}
117
118static ssize_t otp_show(struct device *dev,
119			struct device_attribute *attr, char *buf)
120{
121	u16 addr;
122	u8 otp[OTP_ZONE_SIZE];
123	char *str = buf;
124	struct i2c_client *client = to_i2c_client(dev);
125	int i;
126
127	for (addr = 0; addr < OTP_ZONE_SIZE/4; addr++) {
128		if (atmel_sha204a_otp_read(client, addr, otp + addr * 4) < 0) {
129			dev_err(dev, "failed to read otp zone\n");
130			break;
131		}
132	}
133
134	for (i = 0; i < addr*2; i++)
135		str += sprintf(str, "%02X", otp[i]);
136	str += sprintf(str, "\n");
137	return str - buf;
138}
139static DEVICE_ATTR_RO(otp);
140
141static struct attribute *atmel_sha204a_attrs[] = {
142	&dev_attr_otp.attr,
143	NULL
144};
145
146static const struct attribute_group atmel_sha204a_groups = {
147	.name = "atsha204a",
148	.attrs = atmel_sha204a_attrs,
149};
150
151static int atmel_sha204a_probe(struct i2c_client *client)
152{
153	struct atmel_i2c_client_priv *i2c_priv;
154	int ret;
155
156	ret = atmel_i2c_probe(client);
157	if (ret)
158		return ret;
159
160	i2c_priv = i2c_get_clientdata(client);
161
162	memset(&i2c_priv->hwrng, 0, sizeof(i2c_priv->hwrng));
163
164	i2c_priv->hwrng.name = dev_name(&client->dev);
165	i2c_priv->hwrng.read = atmel_sha204a_rng_read;
166
167	/*
168	 * According to review by Bill Cox [1], this HWRNG has very low entropy.
169	 * [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html
170	 */
171	i2c_priv->hwrng.quality = 1;
172
173	ret = devm_hwrng_register(&client->dev, &i2c_priv->hwrng);
174	if (ret)
175		dev_warn(&client->dev, "failed to register RNG (%d)\n", ret);
176
177	/* otp read out */
178	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
179		return -ENODEV;
180
181	ret = sysfs_create_group(&client->dev.kobj, &atmel_sha204a_groups);
182	if (ret) {
183		dev_err(&client->dev, "failed to register sysfs entry\n");
184		return ret;
185	}
186
187	return ret;
188}
189
190static void atmel_sha204a_remove(struct i2c_client *client)
191{
192	struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
193
194	if (atomic_read(&i2c_priv->tfm_count)) {
195		dev_emerg(&client->dev, "Device is busy, will remove it anyhow\n");
196		return;
197	}
198
199	sysfs_remove_group(&client->dev.kobj, &atmel_sha204a_groups);
200
201	kfree((void *)i2c_priv->hwrng.priv);
202}
203
204static const struct of_device_id atmel_sha204a_dt_ids[] __maybe_unused = {
205	{ .compatible = "atmel,atsha204", },
206	{ .compatible = "atmel,atsha204a", },
207	{ /* sentinel */ }
208};
209MODULE_DEVICE_TABLE(of, atmel_sha204a_dt_ids);
210
211static const struct i2c_device_id atmel_sha204a_id[] = {
212	{ "atsha204" },
213	{ "atsha204a" },
214	{ /* sentinel */ }
215};
216MODULE_DEVICE_TABLE(i2c, atmel_sha204a_id);
217
218static struct i2c_driver atmel_sha204a_driver = {
219	.probe			= atmel_sha204a_probe,
220	.remove			= atmel_sha204a_remove,
221	.id_table		= atmel_sha204a_id,
222
223	.driver.name		= "atmel-sha204a",
224	.driver.of_match_table	= of_match_ptr(atmel_sha204a_dt_ids),
225};
226
227static int __init atmel_sha204a_init(void)
228{
229	return i2c_add_driver(&atmel_sha204a_driver);
230}
231
232static void __exit atmel_sha204a_exit(void)
233{
234	atmel_i2c_flush_queue();
235	i2c_del_driver(&atmel_sha204a_driver);
236}
237
238module_init(atmel_sha204a_init);
239module_exit(atmel_sha204a_exit);
240
241MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
242MODULE_DESCRIPTION("Microchip / Atmel SHA204A (I2C) driver");
243MODULE_LICENSE("GPL v2");