// 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/device.h>
#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>
#include <linux/nvmem-provider.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_MAX_BUSSES               8
#define EE1004_ADDR_SET_PAGE            0x36
#define EE1004_NUM_PAGES                2
#define EE1004_PAGE_SIZE                256
#define EE1004_PAGE_SHIFT               8
#define EE1004_EEPROM_SIZE              (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)

/*
 * 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 ee1004_bus_data {
        struct i2c_adapter *adap;
        struct i2c_client *set_page[EE1004_NUM_PAGES];
        unsigned int dev_count;
        int current_page;
} ee1004_bus_data[EE1004_MAX_BUSSES];

static const struct i2c_device_id ee1004_ids[] = {
        { "ee1004" },
        { }
};
MODULE_DEVICE_TABLE(i2c, ee1004_ids);

/*-------------------------------------------------------------------------*/

static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
{
        int i;

        for (i = 0; i < EE1004_MAX_BUSSES; i++)
                if (ee1004_bus_data[i].adap == adap)
                        return ee1004_bus_data + i;

        /* If not existent yet, create new entry */
        for (i = 0; i < EE1004_MAX_BUSSES; i++)
                if (!ee1004_bus_data[i].adap) {
                        ee1004_bus_data[i].adap = adap;
                        return ee1004_bus_data + i;
                }

        return NULL;
}

static int ee1004_get_current_page(struct ee1004_bus_data *bd)
{
        int err;

        err = i2c_smbus_read_byte(bd->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 int ee1004_set_current_page(struct i2c_client *client, int page)
{
        struct ee1004_bus_data *bd = i2c_get_clientdata(client);
        int ret;

        if (page == bd->current_page)
                return 0;

        /* Data is ignored */
        ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
        /*
         * 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 (ret == -ENXIO && ee1004_get_current_page(bd) == page)
                ret = 0;
        if (ret < 0) {
                dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
                return ret;
        }

        dev_dbg(&client->dev, "Selected page %d\n", page);
        bd->current_page = page;

        return 0;
}

static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
                                  unsigned int offset, size_t count)
{
        int status, page;

        page = offset >> EE1004_PAGE_SHIFT;
        offset &= (1 << EE1004_PAGE_SHIFT) - 1;

        status = ee1004_set_current_page(client, page);
        if (status)
                return status;

        /* Can't cross page boundaries */
        if (offset + count > EE1004_PAGE_SIZE)
                count = EE1004_PAGE_SIZE - offset;

        if (count > I2C_SMBUS_BLOCK_MAX)
                count = I2C_SMBUS_BLOCK_MAX;

        return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
}

static int ee1004_read(void *priv, unsigned int off, void *val, size_t count)
{
        struct i2c_client *client = priv;
        char *buf = val;
        int ret;

        if (unlikely(!count))
                return count;

        if (off + count > EE1004_EEPROM_SIZE)
                return -EINVAL;

        /*
         * Read data from chip, protecting against concurrent access to
         * other EE1004 SPD EEPROMs on the same adapter.
         */
        mutex_lock(&ee1004_bus_lock);

        while (count) {
                ret = ee1004_eeprom_read(client, buf, off, count);
                if (ret < 0) {
                        mutex_unlock(&ee1004_bus_lock);
                        return ret;
                }

                buf += ret;
                off += ret;
                count -= ret;
        }

        mutex_unlock(&ee1004_bus_lock);

        return 0;
}

static void ee1004_probe_temp_sensor(struct i2c_client *client)
{
        struct i2c_board_info info = { .type = "jc42" };
        unsigned short addr = 0x18 | (client->addr & 7);
        unsigned short addr_list[] = { addr, I2C_CLIENT_END };
        u8 data[2];
        int ret;

        /* byte 14, bit 7 is set if temp sensor is present */
        ret = ee1004_eeprom_read(client, data, 14, 1);
        if (ret != 1)
                return;

        if (!(data[0] & BIT(7))) {
                /*
                 * If the SPD data suggests that there is no temperature
                 * sensor, it may still be there for SPD revision 1.0.
                 * See SPD Annex L, Revision 1 and 2, for details.
                 * Check DIMM type and SPD revision; if it is a DDR4
                 * with SPD revision 1.0, check the thermal sensor address
                 * and instantiate the jc42 driver if a chip is found at
                 * that address.
                 * It is not necessary to check if there is a chip at the
                 * temperature sensor address since i2c_new_scanned_device()
                 * will do that and return silently if no chip is found.
                 */
                ret = ee1004_eeprom_read(client, data, 1, 2);
                if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c)
                        return;
        }
        i2c_new_scanned_device(client->adapter, &info, addr_list, NULL);
}

static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
{
        if (--bd->dev_count == 0) {
                while (--idx >= 0)
                        i2c_unregister_device(bd->set_page[idx]);
                memset(bd, 0, sizeof(struct ee1004_bus_data));
        }
}

static void ee1004_cleanup_bus_data(void *data)
{
        struct ee1004_bus_data *bd = data;

        /* Remove page select clients if this is the last device */
        mutex_lock(&ee1004_bus_lock);
        ee1004_cleanup(EE1004_NUM_PAGES, bd);
        mutex_unlock(&ee1004_bus_lock);
}

static int ee1004_init_bus_data(struct i2c_client *client)
{
        struct ee1004_bus_data *bd;
        int err, cnr = 0;

        bd = ee1004_get_bus_data(client->adapter);
        if (!bd)
                return dev_err_probe(&client->dev, -ENOSPC, "Only %d busses supported",
                                     EE1004_MAX_BUSSES);

        i2c_set_clientdata(client, bd);

        if (++bd->dev_count == 1) {
                /* Use 2 dummy devices for page select command */
                for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
                        struct i2c_client *cl;

                        cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
                        if (IS_ERR(cl)) {
                                err = PTR_ERR(cl);
                                goto err_out;
                        }

                        bd->set_page[cnr] = cl;
                }

                /* Remember current page to avoid unneeded page select */
                err = ee1004_get_current_page(bd);
                if (err < 0)
                        goto err_out;

                dev_dbg(&client->dev, "Currently selected page: %d\n", err);
                bd->current_page = err;
        }

        return 0;

err_out:
        ee1004_cleanup(cnr, bd);

        return err;
}

static int ee1004_probe(struct i2c_client *client)
{
        struct nvmem_config config = {
                .dev = &client->dev,
                .name = dev_name(&client->dev),
                .id = NVMEM_DEVID_NONE,
                .owner = THIS_MODULE,
                .type = NVMEM_TYPE_EEPROM,
                .read_only = true,
                .root_only = false,
                .reg_read = ee1004_read,
                .size = EE1004_EEPROM_SIZE,
                .word_size = 1,
                .stride = 1,
                .priv = client,
                .compat = true,
                .base_dev = &client->dev,
        };
        struct nvmem_device *ndev;
        int err;

        /* Make sure we can operate on this adapter */
        if (!i2c_check_functionality(client->adapter,
                                     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
            !i2c_check_functionality(client->adapter,
                                     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
                return -EPFNOSUPPORT;

        err = i2c_smbus_read_byte(client);
        if (err < 0)
                return -ENODEV;

        mutex_lock(&ee1004_bus_lock);

        err = ee1004_init_bus_data(client);
        if (err < 0) {
                mutex_unlock(&ee1004_bus_lock);
                return err;
        }

        ee1004_probe_temp_sensor(client);

        mutex_unlock(&ee1004_bus_lock);

        err = devm_add_action_or_reset(&client->dev, ee1004_cleanup_bus_data,
                                       i2c_get_clientdata(client));
        if (err < 0)
                return err;

        ndev = devm_nvmem_register(&client->dev, &config);
        if (IS_ERR(ndev))
                return PTR_ERR(ndev);

        dev_info(&client->dev,
                 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
                 EE1004_EEPROM_SIZE);

        return 0;
}

/*-------------------------------------------------------------------------*/

static struct i2c_driver ee1004_driver = {
        .driver = {
                .name = "ee1004",
        },
        .probe = ee1004_probe,
        .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");