Orange Pi5 kernel

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * ee1004 - driver for DDR4 SPD EEPROMs
 *
 * Copyright (C) 2017-2019 Jean Delvare
 *
 * Based on the at24 driver:
 * Copyright (C) 2005-2007 David Brownell
 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 */
 
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/mutex.h>
 
/*
 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
 * specification. These are 512-byte EEPROMs using a single I2C address
 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
 *
 * Therefore we need to request these 2 additional addresses, and serialize
 * access to all such EEPROMs with a single mutex.
 *
 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
 * We use SMBus access even if I2C is available, these EEPROMs are small
 * enough, and reading from them infrequent enough, that we favor simplicity
 * over performance.
 */
 
#define EE1004_ADDR_SET_PAGE		0x36
#define EE1004_EEPROM_SIZE		512
#define EE1004_PAGE_SIZE		256
#define EE1004_PAGE_SHIFT		8
 
/*
 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
 * from page selection to end of read.
 */
static DEFINE_MUTEX(ee1004_bus_lock);
static struct i2c_client *ee1004_set_page[2];
static unsigned int ee1004_dev_count;
static int ee1004_current_page;
 
static const struct i2c_device_id ee1004_ids[] = {
<------>{ "ee1004", 0 },
<------>{ }
};
MODULE_DEVICE_TABLE(i2c, ee1004_ids);
 
/*-------------------------------------------------------------------------*/
 
static int ee1004_get_current_page(void)
{
<------>int err;
 
<------>err = i2c_smbus_read_byte(ee1004_set_page[0]);
<------>if (err == -ENXIO) {
<------><------>/* Nack means page 1 is selected */
<------><------>return 1;
<------>}
<------>if (err < 0) {
<------><------>/* Anything else is a real error, bail out */
<------><------>return err;
<------>}
 
<------>/* Ack means page 0 is selected, returned value meaningless */
<------>return 0;
}
 
static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
<------><------><------><------>  unsigned int offset, size_t count)
{
<------>int status;
 
<------>if (count > I2C_SMBUS_BLOCK_MAX)
<------><------>count = I2C_SMBUS_BLOCK_MAX;
<------>/* Can't cross page boundaries */
<------>if (unlikely(offset + count > EE1004_PAGE_SIZE))
<------><------>count = EE1004_PAGE_SIZE - offset;
 
<------>if (count > I2C_SMBUS_BLOCK_MAX)
<------><------>count = I2C_SMBUS_BLOCK_MAX;
 
<------>status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
<------><------><------><------><------><------><------>   count, buf);
<------>dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
 
<------>return status;
}
 
static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
<------><------><------>   struct bin_attribute *bin_attr,
<------><------><------>   char *buf, loff_t off, size_t count)
{
<------>struct device *dev = kobj_to_dev(kobj);
<------>struct i2c_client *client = to_i2c_client(dev);
<------>size_t requested = count;
<------>int page;
 
<------>if (unlikely(!count))
<------><------>return count;
 
<------>page = off >> EE1004_PAGE_SHIFT;
<------>if (unlikely(page > 1))
<------><------>return 0;
<------>off &= (1 << EE1004_PAGE_SHIFT) - 1;
 
<------>/*
<------> * Read data from chip, protecting against concurrent access to
<------> * other EE1004 SPD EEPROMs on the same adapter.
<------> */
<------>mutex_lock(&ee1004_bus_lock);
 
<------>while (count) {
<------><------>int status;
 
<------><------>/* Select page */
<------><------>if (page != ee1004_current_page) {
<------><------><------>/* Data is ignored */
<------><------><------>status = i2c_smbus_write_byte(ee1004_set_page[page],
<------><------><------><------><------><------>      0x00);
<------><------><------>if (status == -ENXIO) {
<------><------><------><------>/*
<------><------><------><------> * Don't give up just yet. Some memory
<------><------><------><------> * modules will select the page but not
<------><------><------><------> * ack the command. Check which page is
<------><------><------><------> * selected now.
<------><------><------><------> */
<------><------><------><------>if (ee1004_get_current_page() == page)
<------><------><------><------><------>status = 0;
<------><------><------>}
<------><------><------>if (status < 0) {
<------><------><------><------>dev_err(dev, "Failed to select page %d (%d)\n",
<------><------><------><------><------>page, status);
<------><------><------><------>mutex_unlock(&ee1004_bus_lock);
<------><------><------><------>return status;
<------><------><------>}
<------><------><------>dev_dbg(dev, "Selected page %d\n", page);
<------><------><------>ee1004_current_page = page;
<------><------>}
 
<------><------>status = ee1004_eeprom_read(client, buf, off, count);
<------><------>if (status < 0) {
<------><------><------>mutex_unlock(&ee1004_bus_lock);
<------><------><------>return status;
<------><------>}
<------><------>buf += status;
<------><------>off += status;
<------><------>count -= status;
 
<------><------>if (off == EE1004_PAGE_SIZE) {
<------><------><------>page++;
<------><------><------>off = 0;
<------><------>}
<------>}
 
<------>mutex_unlock(&ee1004_bus_lock);
 
<------>return requested;
}
 
static const struct bin_attribute eeprom_attr = {
<------>.attr = {
<------><------>.name = "eeprom",
<------><------>.mode = 0444,
<------>},
<------>.size = EE1004_EEPROM_SIZE,
<------>.read = ee1004_read,
};
 
static int ee1004_probe(struct i2c_client *client,
<------><------><------>const struct i2c_device_id *id)
{
<------>int err, cnr = 0;
<------>const char *slow = NULL;
 
<------>/* Make sure we can operate on this adapter */
<------>if (!i2c_check_functionality(client->adapter,
<------><------><------><------>     I2C_FUNC_SMBUS_READ_BYTE |
<------><------><------><------>     I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
<------><------>if (i2c_check_functionality(client->adapter,
<------><------><------><------>     I2C_FUNC_SMBUS_READ_BYTE |
<------><------><------><------>     I2C_FUNC_SMBUS_READ_WORD_DATA))
<------><------><------>slow = "word";
<------><------>else if (i2c_check_functionality(client->adapter,
<------><------><------><------>     I2C_FUNC_SMBUS_READ_BYTE |
<------><------><------><------>     I2C_FUNC_SMBUS_READ_BYTE_DATA))
<------><------><------>slow = "byte";
<------><------>else
<------><------><------>return -EPFNOSUPPORT;
<------>}
 
<------>/* Use 2 dummy devices for page select command */
<------>mutex_lock(&ee1004_bus_lock);
<------>if (++ee1004_dev_count == 1) {
<------><------>for (cnr = 0; cnr < 2; cnr++) {
<------><------><------>ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
<------><------><------><------><------><------>EE1004_ADDR_SET_PAGE + cnr);
<------><------><------>if (IS_ERR(ee1004_set_page[cnr])) {
<------><------><------><------>dev_err(&client->dev,
<------><------><------><------><------>"address 0x%02x unavailable\n",
<------><------><------><------><------>EE1004_ADDR_SET_PAGE + cnr);
<------><------><------><------>err = PTR_ERR(ee1004_set_page[cnr]);
<------><------><------><------>goto err_clients;
<------><------><------>}
<------><------>}
<------>} else if (i2c_adapter_id(client->adapter) !=
<------><------>   i2c_adapter_id(ee1004_set_page[0]->adapter)) {
<------><------>dev_err(&client->dev,
<------><------><------>"Driver only supports devices on a single I2C bus\n");
<------><------>err = -EOPNOTSUPP;
<------><------>goto err_clients;
<------>}
 
<------>/* Remember current page to avoid unneeded page select */
<------>err = ee1004_get_current_page();
<------>if (err < 0)
<------><------>goto err_clients;
<------>ee1004_current_page = err;
<------>dev_dbg(&client->dev, "Currently selected page: %d\n",
<------><------>ee1004_current_page);
<------>mutex_unlock(&ee1004_bus_lock);
 
<------>/* Create the sysfs eeprom file */
<------>err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
<------>if (err)
<------><------>goto err_clients_lock;
 
<------>dev_info(&client->dev,
<------><------> "%u byte EE1004-compliant SPD EEPROM, read-only\n",
<------><------> EE1004_EEPROM_SIZE);
<------>if (slow)
<------><------>dev_notice(&client->dev,
<------><------><------>   "Falling back to %s reads, performance will suffer\n",
<------><------><------>   slow);
 
<------>return 0;
 
 err_clients_lock:
<------>mutex_lock(&ee1004_bus_lock);
 err_clients:
<------>if (--ee1004_dev_count == 0) {
<------><------>for (cnr--; cnr >= 0; cnr--) {
<------><------><------>i2c_unregister_device(ee1004_set_page[cnr]);
<------><------><------>ee1004_set_page[cnr] = NULL;
<------><------>}
<------>}
<------>mutex_unlock(&ee1004_bus_lock);
 
<------>return err;
}
 
static int ee1004_remove(struct i2c_client *client)
{
<------>int i;
 
<------>sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
 
<------>/* Remove page select clients if this is the last device */
<------>mutex_lock(&ee1004_bus_lock);
<------>if (--ee1004_dev_count == 0) {
<------><------>for (i = 0; i < 2; i++) {
<------><------><------>i2c_unregister_device(ee1004_set_page[i]);
<------><------><------>ee1004_set_page[i] = NULL;
<------><------>}
<------>}
<------>mutex_unlock(&ee1004_bus_lock);
 
<------>return 0;
}
 
/*-------------------------------------------------------------------------*/
 
static struct i2c_driver ee1004_driver = {
<------>.driver = {
<------><------>.name = "ee1004",
<------>},
<------>.probe = ee1004_probe,
<------>.remove = ee1004_remove,
<------>.id_table = ee1004_ids,
};
module_i2c_driver(ee1004_driver);
 
MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
MODULE_AUTHOR("Jean Delvare");
MODULE_LICENSE("GPL");