1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * ee1004 - driver for DDR4 SPD EEPROMs
  4 *
  5 * Copyright (C) 2017-2019 Jean Delvare
  6 *
  7 * Based on the at24 driver:
  8 * Copyright (C) 2005-2007 David Brownell
  9 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 10 */
 11
 12#include <linux/i2c.h>
 13#include <linux/init.h>
 14#include <linux/kernel.h>
 15#include <linux/mod_devicetable.h>
 16#include <linux/module.h>
 17#include <linux/mutex.h>
 18
 19/*
 20 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
 21 * specification. These are 512-byte EEPROMs using a single I2C address
 22 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
 23 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
 24 *
 25 * Therefore we need to request these 2 additional addresses, and serialize
 26 * access to all such EEPROMs with a single mutex.
 27 *
 28 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
 29 * We use SMBus access even if I2C is available, these EEPROMs are small
 30 * enough, and reading from them infrequent enough, that we favor simplicity
 31 * over performance.
 32 */
 33
 34#define EE1004_ADDR_SET_PAGE		0x36
 35#define EE1004_NUM_PAGES		2
 36#define EE1004_PAGE_SIZE		256
 37#define EE1004_PAGE_SHIFT		8
 38#define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
 39
 40/*
 41 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
 42 * from page selection to end of read.
 43 */
 44static DEFINE_MUTEX(ee1004_bus_lock);
 45static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
 46static unsigned int ee1004_dev_count;
 47static int ee1004_current_page;
 48
 49static const struct i2c_device_id ee1004_ids[] = {
 50	{ "ee1004", 0 },
 51	{ }
 52};
 53MODULE_DEVICE_TABLE(i2c, ee1004_ids);
 54
 55/*-------------------------------------------------------------------------*/
 56
 57static int ee1004_get_current_page(void)
 58{
 59	int err;
 60
 61	err = i2c_smbus_read_byte(ee1004_set_page[0]);
 62	if (err == -ENXIO) {
 63		/* Nack means page 1 is selected */
 64		return 1;
 65	}
 66	if (err < 0) {
 67		/* Anything else is a real error, bail out */
 68		return err;
 69	}
 70
 71	/* Ack means page 0 is selected, returned value meaningless */
 72	return 0;
 73}
 74
 75static int ee1004_set_current_page(struct device *dev, int page)
 76{
 77	int ret;
 78
 79	if (page == ee1004_current_page)
 80		return 0;
 81
 82	/* Data is ignored */
 83	ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
 84	/*
 85	 * Don't give up just yet. Some memory modules will select the page
 86	 * but not ack the command. Check which page is selected now.
 87	 */
 88	if (ret == -ENXIO && ee1004_get_current_page() == page)
 89		ret = 0;
 90	if (ret < 0) {
 91		dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
 92		return ret;
 93	}
 94
 95	dev_dbg(dev, "Selected page %d\n", page);
 96	ee1004_current_page = page;
 97
 98	return 0;
 99}
100
101static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
102				  unsigned int offset, size_t count)
103{
104	int status, page;
105
106	page = offset >> EE1004_PAGE_SHIFT;
107	offset &= (1 << EE1004_PAGE_SHIFT) - 1;
108
109	status = ee1004_set_current_page(&client->dev, page);
110	if (status)
111		return status;
112
113	/* Can't cross page boundaries */
114	if (offset + count > EE1004_PAGE_SIZE)
115		count = EE1004_PAGE_SIZE - offset;
116
117	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
118}
119
120static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
121			   struct bin_attribute *bin_attr,
122			   char *buf, loff_t off, size_t count)
123{
124	struct i2c_client *client = kobj_to_i2c_client(kobj);
125	size_t requested = count;
126	int ret = 0;
127
128	/*
129	 * Read data from chip, protecting against concurrent access to
130	 * other EE1004 SPD EEPROMs on the same adapter.
131	 */
132	mutex_lock(&ee1004_bus_lock);
133
134	while (count) {
135		ret = ee1004_eeprom_read(client, buf, off, count);
136		if (ret < 0)
137			goto out;
138
139		buf += ret;
140		off += ret;
141		count -= ret;
142	}
143out:
144	mutex_unlock(&ee1004_bus_lock);
145
146	return ret < 0 ? ret : requested;
147}
148
149static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
150
151static struct bin_attribute *ee1004_attrs[] = {
152	&bin_attr_eeprom,
153	NULL
154};
155
156BIN_ATTRIBUTE_GROUPS(ee1004);
157
158static void ee1004_cleanup(int idx)
159{
160	if (--ee1004_dev_count == 0)
161		while (--idx >= 0) {
162			i2c_unregister_device(ee1004_set_page[idx]);
163			ee1004_set_page[idx] = NULL;
164		}
165}
166
167static int ee1004_probe(struct i2c_client *client)
168{
169	int err, cnr = 0;
170
171	/* Make sure we can operate on this adapter */
172	if (!i2c_check_functionality(client->adapter,
173				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
174	    !i2c_check_functionality(client->adapter,
175				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
176		return -EPFNOSUPPORT;
177
178	/* Use 2 dummy devices for page select command */
179	mutex_lock(&ee1004_bus_lock);
180	if (++ee1004_dev_count == 1) {
181		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
182			struct i2c_client *cl;
183
184			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
185			if (IS_ERR(cl)) {
186				err = PTR_ERR(cl);
187				goto err_clients;
188			}
189			ee1004_set_page[cnr] = cl;
190		}
191
192		/* Remember current page to avoid unneeded page select */
193		err = ee1004_get_current_page();
194		if (err < 0)
195			goto err_clients;
196		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
197		ee1004_current_page = err;
198	} else if (client->adapter != ee1004_set_page[0]->adapter) {
199		dev_err(&client->dev,
200			"Driver only supports devices on a single I2C bus\n");
201		err = -EOPNOTSUPP;
202		goto err_clients;
203	}
204	mutex_unlock(&ee1004_bus_lock);
205
206	dev_info(&client->dev,
207		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
208		 EE1004_EEPROM_SIZE);
209
210	return 0;
211
212 err_clients:
213	ee1004_cleanup(cnr);
214	mutex_unlock(&ee1004_bus_lock);
215
216	return err;
217}
218
219static int ee1004_remove(struct i2c_client *client)
220{
221	/* Remove page select clients if this is the last device */
222	mutex_lock(&ee1004_bus_lock);
223	ee1004_cleanup(EE1004_NUM_PAGES);
224	mutex_unlock(&ee1004_bus_lock);
225
226	return 0;
227}
228
229/*-------------------------------------------------------------------------*/
230
231static struct i2c_driver ee1004_driver = {
232	.driver = {
233		.name = "ee1004",
234		.dev_groups = ee1004_groups,
235	},
236	.probe_new = ee1004_probe,
237	.remove = ee1004_remove,
238	.id_table = ee1004_ids,
239};
240module_i2c_driver(ee1004_driver);
241
242MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
243MODULE_AUTHOR("Jean Delvare");
244MODULE_LICENSE("GPL");