245 lines
6.1 KiB
C
245 lines
6.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* ee1004 - driver for DDR4 SPD EEPROMs
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*
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* Copyright (C) 2017-2019 Jean Delvare
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*
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* Based on the at24 driver:
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* Copyright (C) 2005-2007 David Brownell
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* Copyright (C) 2008 Wolfram Sang, Pengutronix
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*/
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#include <linux/i2c.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/mod_devicetable.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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/*
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* DDR4 memory modules use special EEPROMs following the Jedec EE1004
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* specification. These are 512-byte EEPROMs using a single I2C address
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* in the 0x50-0x57 range for data. One of two 256-byte page is selected
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* by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
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*
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* Therefore we need to request these 2 additional addresses, and serialize
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* access to all such EEPROMs with a single mutex.
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*
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* We assume it is safe to read up to 32 bytes at once from these EEPROMs.
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* We use SMBus access even if I2C is available, these EEPROMs are small
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* enough, and reading from them infrequent enough, that we favor simplicity
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* over performance.
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*/
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#define EE1004_ADDR_SET_PAGE 0x36
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#define EE1004_NUM_PAGES 2
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#define EE1004_PAGE_SIZE 256
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#define EE1004_PAGE_SHIFT 8
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#define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
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/*
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* Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
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* from page selection to end of read.
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*/
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static DEFINE_MUTEX(ee1004_bus_lock);
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static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
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static unsigned int ee1004_dev_count;
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static int ee1004_current_page;
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static const struct i2c_device_id ee1004_ids[] = {
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{ "ee1004", 0 },
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{ }
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};
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MODULE_DEVICE_TABLE(i2c, ee1004_ids);
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/*-------------------------------------------------------------------------*/
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static int ee1004_get_current_page(void)
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{
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int err;
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err = i2c_smbus_read_byte(ee1004_set_page[0]);
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if (err == -ENXIO) {
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/* Nack means page 1 is selected */
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return 1;
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}
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if (err < 0) {
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/* Anything else is a real error, bail out */
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return err;
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}
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/* Ack means page 0 is selected, returned value meaningless */
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return 0;
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}
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static int ee1004_set_current_page(struct device *dev, int page)
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{
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int ret;
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if (page == ee1004_current_page)
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return 0;
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/* Data is ignored */
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ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
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/*
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* Don't give up just yet. Some memory modules will select the page
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* but not ack the command. Check which page is selected now.
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*/
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if (ret == -ENXIO && ee1004_get_current_page() == page)
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ret = 0;
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if (ret < 0) {
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dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
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return ret;
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}
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dev_dbg(dev, "Selected page %d\n", page);
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ee1004_current_page = page;
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return 0;
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}
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static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
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unsigned int offset, size_t count)
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{
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int status, page;
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page = offset >> EE1004_PAGE_SHIFT;
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offset &= (1 << EE1004_PAGE_SHIFT) - 1;
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status = ee1004_set_current_page(&client->dev, page);
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if (status)
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return status;
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/* Can't cross page boundaries */
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if (offset + count > EE1004_PAGE_SIZE)
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count = EE1004_PAGE_SIZE - offset;
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return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
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}
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static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
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struct bin_attribute *bin_attr,
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char *buf, loff_t off, size_t count)
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{
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struct i2c_client *client = kobj_to_i2c_client(kobj);
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size_t requested = count;
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int ret = 0;
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/*
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* Read data from chip, protecting against concurrent access to
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* other EE1004 SPD EEPROMs on the same adapter.
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*/
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mutex_lock(&ee1004_bus_lock);
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while (count) {
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ret = ee1004_eeprom_read(client, buf, off, count);
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if (ret < 0)
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goto out;
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buf += ret;
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off += ret;
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count -= ret;
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}
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out:
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mutex_unlock(&ee1004_bus_lock);
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return ret < 0 ? ret : requested;
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}
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static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
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static struct bin_attribute *ee1004_attrs[] = {
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&bin_attr_eeprom,
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NULL
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};
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BIN_ATTRIBUTE_GROUPS(ee1004);
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static void ee1004_cleanup(int idx)
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{
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if (--ee1004_dev_count == 0)
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while (--idx >= 0) {
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i2c_unregister_device(ee1004_set_page[idx]);
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ee1004_set_page[idx] = NULL;
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}
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}
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static int ee1004_probe(struct i2c_client *client)
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{
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int err, cnr = 0;
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/* Make sure we can operate on this adapter */
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if (!i2c_check_functionality(client->adapter,
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I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
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!i2c_check_functionality(client->adapter,
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I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
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return -EPFNOSUPPORT;
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/* Use 2 dummy devices for page select command */
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mutex_lock(&ee1004_bus_lock);
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if (++ee1004_dev_count == 1) {
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for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
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struct i2c_client *cl;
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cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
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if (IS_ERR(cl)) {
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err = PTR_ERR(cl);
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goto err_clients;
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}
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ee1004_set_page[cnr] = cl;
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}
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/* Remember current page to avoid unneeded page select */
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err = ee1004_get_current_page();
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if (err < 0)
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goto err_clients;
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dev_dbg(&client->dev, "Currently selected page: %d\n", err);
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ee1004_current_page = err;
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} else if (client->adapter != ee1004_set_page[0]->adapter) {
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dev_err(&client->dev,
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"Driver only supports devices on a single I2C bus\n");
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err = -EOPNOTSUPP;
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goto err_clients;
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}
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mutex_unlock(&ee1004_bus_lock);
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dev_info(&client->dev,
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"%u byte EE1004-compliant SPD EEPROM, read-only\n",
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EE1004_EEPROM_SIZE);
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return 0;
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err_clients:
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ee1004_cleanup(cnr);
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mutex_unlock(&ee1004_bus_lock);
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return err;
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}
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static int ee1004_remove(struct i2c_client *client)
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{
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/* Remove page select clients if this is the last device */
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mutex_lock(&ee1004_bus_lock);
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ee1004_cleanup(EE1004_NUM_PAGES);
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mutex_unlock(&ee1004_bus_lock);
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return 0;
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}
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/*-------------------------------------------------------------------------*/
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static struct i2c_driver ee1004_driver = {
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.driver = {
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.name = "ee1004",
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.dev_groups = ee1004_groups,
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},
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.probe_new = ee1004_probe,
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.remove = ee1004_remove,
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.id_table = ee1004_ids,
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};
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module_i2c_driver(ee1004_driver);
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MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
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MODULE_AUTHOR("Jean Delvare");
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MODULE_LICENSE("GPL");
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