299 lines
7.3 KiB
C
299 lines
7.3 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_EEPROM_SIZE 512
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#define EE1004_PAGE_SIZE 256
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#define EE1004_PAGE_SHIFT 8
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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[2];
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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 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;
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if (count > I2C_SMBUS_BLOCK_MAX)
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count = I2C_SMBUS_BLOCK_MAX;
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/* Can't cross page boundaries */
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if (unlikely(offset + count > EE1004_PAGE_SIZE))
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count = EE1004_PAGE_SIZE - offset;
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status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
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count, buf);
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dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
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return status;
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}
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static ssize_t ee1004_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 device *dev = kobj_to_dev(kobj);
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struct i2c_client *client = to_i2c_client(dev);
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size_t requested = count;
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int page;
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if (unlikely(!count))
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return count;
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page = off >> EE1004_PAGE_SHIFT;
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if (unlikely(page > 1))
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return 0;
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off &= (1 << EE1004_PAGE_SHIFT) - 1;
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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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int status;
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/* Select page */
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if (page != ee1004_current_page) {
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/* Data is ignored */
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status = i2c_smbus_write_byte(ee1004_set_page[page],
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0x00);
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if (status == -ENXIO) {
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/*
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* Don't give up just yet. Some memory
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* modules will select the page but not
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* ack the command. Check which page is
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* selected now.
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*/
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if (ee1004_get_current_page() == page)
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status = 0;
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}
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if (status < 0) {
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dev_err(dev, "Failed to select page %d (%d)\n",
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page, status);
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mutex_unlock(&ee1004_bus_lock);
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return status;
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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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}
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status = ee1004_eeprom_read(client, buf, off, count);
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if (status < 0) {
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mutex_unlock(&ee1004_bus_lock);
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return status;
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}
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buf += status;
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off += status;
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count -= status;
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if (off == EE1004_PAGE_SIZE) {
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page++;
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off = 0;
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}
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}
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mutex_unlock(&ee1004_bus_lock);
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return requested;
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}
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static const struct bin_attribute eeprom_attr = {
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.attr = {
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.name = "eeprom",
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.mode = 0444,
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},
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.size = EE1004_EEPROM_SIZE,
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.read = ee1004_read,
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};
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static int ee1004_probe(struct i2c_client *client,
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const struct i2c_device_id *id)
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{
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int err, cnr = 0;
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const char *slow = NULL;
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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_READ_BYTE |
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I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
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if (i2c_check_functionality(client->adapter,
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I2C_FUNC_SMBUS_READ_BYTE |
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I2C_FUNC_SMBUS_READ_WORD_DATA))
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slow = "word";
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else if (i2c_check_functionality(client->adapter,
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I2C_FUNC_SMBUS_READ_BYTE |
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I2C_FUNC_SMBUS_READ_BYTE_DATA))
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slow = "byte";
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else
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return -EPFNOSUPPORT;
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}
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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 < 2; cnr++) {
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ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
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EE1004_ADDR_SET_PAGE + cnr);
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if (IS_ERR(ee1004_set_page[cnr])) {
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dev_err(&client->dev,
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"address 0x%02x unavailable\n",
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EE1004_ADDR_SET_PAGE + cnr);
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err = PTR_ERR(ee1004_set_page[cnr]);
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goto err_clients;
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}
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}
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} else if (i2c_adapter_id(client->adapter) !=
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i2c_adapter_id(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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/* 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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ee1004_current_page = err;
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dev_dbg(&client->dev, "Currently selected page: %d\n",
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ee1004_current_page);
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mutex_unlock(&ee1004_bus_lock);
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/* Create the sysfs eeprom file */
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err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
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if (err)
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goto err_clients_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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if (slow)
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dev_notice(&client->dev,
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"Falling back to %s reads, performance will suffer\n",
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slow);
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return 0;
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err_clients_lock:
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mutex_lock(&ee1004_bus_lock);
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err_clients:
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if (--ee1004_dev_count == 0) {
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for (cnr--; cnr >= 0; cnr--) {
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i2c_unregister_device(ee1004_set_page[cnr]);
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ee1004_set_page[cnr] = NULL;
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}
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}
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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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int i;
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sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
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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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if (--ee1004_dev_count == 0) {
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for (i = 0; i < 2; i++) {
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i2c_unregister_device(ee1004_set_page[i]);
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ee1004_set_page[i] = NULL;
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}
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}
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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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},
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.probe = 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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static int __init ee1004_init(void)
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{
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return i2c_add_driver(&ee1004_driver);
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}
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module_init(ee1004_init);
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static void __exit ee1004_exit(void)
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{
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i2c_del_driver(&ee1004_driver);
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}
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module_exit(ee1004_exit);
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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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