/*
    max6875.c - driver for MAX6874/MAX6875

    Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>

    Based on i2c/chips/eeprom.c

    The MAX6875 has two EEPROM sections: config and user.
    At reset, the config EEPROM is read into the registers.

    This driver make 3 binary files available in sysfs:
      reg_config    - direct access to the registers
      eeprom_config - acesses configuration eeprom space
      eeprom_user   - free for application use

    In our application, we put device serial & model numbers in user eeprom.

    Notes:
      1) The datasheet says that register 0x44 / EEPROM 0x8044 should NOT
         be overwritten, so the driver explicitly prevents that.
      2) It's a good idea to keep the config (0x45) locked in config EEPROM.
         You can temporarily enable config writes by changing register 0x45.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; version 2 of the License.
*/

#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/i2c-sensor.h>

/* Addresses to scan */
/* No address scanned by default, as this could corrupt standard EEPROMS. */
static unsigned short normal_i2c[] = {I2C_CLIENT_END};
static unsigned int normal_isa[] = {I2C_CLIENT_ISA_END};

/* Insmod parameters */
SENSORS_INSMOD_1(max6875);

/* this param will prevent 'accidental' writes to the eeprom */
static int allow_write = 0;
module_param(allow_write, int, 0);
MODULE_PARM_DESC(allow_write,
		 "Enable write access:\n"
		 "*0: Read only\n"
		 " 1: Read/Write access");

/* The MAX6875 can only read/write 16 bytes at a time */
#define SLICE_SIZE			16
#define SLICE_BITS			4

/* CONFIG EEPROM is at addresses 0x8000 - 0x8045, registers are at 0 - 0x45 */
#define CONFIG_EEPROM_BASE		0x8000
#define CONFIG_EEPROM_SIZE		0x0046
#define CONFIG_EEPROM_SLICES		5

/* USER EEPROM is at addresses 0x8100 - 0x82FF */
#define USER_EEPROM_BASE		0x8100
#define USER_EEPROM_SIZE		0x0200
#define USER_EEPROM_SLICES		32

/* MAX6875 commands */
#define MAX6875_CMD_BLOCK_WRITE		0x83
#define MAX6875_CMD_BLOCK_READ		0x84
#define MAX6875_CMD_REBOOT		0x88

enum max6875_area_type {
	max6875_register_config=0,
	max6875_eeprom_config,
	max6875_eeprom_user,
	max6857_max
};

struct eeprom_block {
	enum max6875_area_type	type;
	u8			slices;
	u32			size;
	u32			valid;
	u32			base;
	unsigned long		*updated;
	u8			*data;
};

/* Each client has this additional data */
struct max6875_data {
	struct i2c_client	client;
	struct semaphore	update_lock;
	struct eeprom_block	blocks[max6857_max];
	/* the above structs point into the arrays below */
	u8 data[USER_EEPROM_SIZE + (CONFIG_EEPROM_SIZE*2)];
	unsigned long last_updated[USER_EEPROM_SLICES + (CONFIG_EEPROM_SLICES*2)];
};

static int max6875_attach_adapter(struct i2c_adapter *adapter);
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind);
static int max6875_detach_client(struct i2c_client *client);

/* This is the driver that will be inserted */
static struct i2c_driver max6875_driver = {
	.owner		= THIS_MODULE,
	.name		= "max6875",
	.flags		= I2C_DF_NOTIFY,
	.attach_adapter	= max6875_attach_adapter,
	.detach_client	= max6875_detach_client,
};

static int max6875_update_slice(struct i2c_client *client,
				struct eeprom_block *blk,
				int slice)
{
	struct max6875_data *data = i2c_get_clientdata(client);
	int i, j, addr, count;
	u8 rdbuf[SLICE_SIZE];
	int retval = 0;

	if (slice >= blk->slices)
		return -1;

	down(&data->update_lock);

	if (!(blk->valid & (1 << slice)) ||
	    (jiffies - blk->updated[slice] > 300 * HZ) ||
	    (jiffies < blk->updated[slice])) {
		dev_dbg(&client->dev, "Starting eeprom update, slice %u, base %u\n",
			slice, blk->base);

		addr = blk->base + (slice << SLICE_BITS);
		count = blk->size - (slice << SLICE_BITS);
		if (count > SLICE_SIZE) {
			count = SLICE_SIZE;
		}

		/* Preset the read address */
		if (addr < 0x100) {
			/* select the register */
			if (i2c_smbus_write_byte(client, addr & 0xFF)) {
				dev_dbg(&client->dev, "max6875 register select has failed!\n");
				retval = -1;
				goto exit;
			}
		} else {
			/* select the eeprom */
			if (i2c_smbus_write_byte_data(client, addr >> 8, addr & 0xFF)) {
				dev_dbg(&client->dev, "max6875 address set has failed!\n");
				retval = -1;
				goto exit;
			}
		}

		if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
			if (i2c_smbus_read_i2c_block_data(client, MAX6875_CMD_BLOCK_READ,
							  rdbuf) != SLICE_SIZE)
			{
				retval = -1;
				goto exit;
			}

			memcpy(&blk->data[slice << SLICE_BITS], rdbuf, count);
		} else {
			for (i = 0; i < count; i++) {
				j = i2c_smbus_read_byte(client);
				if (j < 0)
				{
					retval = -1;
					goto exit;
				}
				blk->data[(slice << SLICE_BITS) + i] = (u8) j;
			}
		}
		blk->updated[slice] = jiffies;
		blk->valid |= (1 << slice);
	}
	exit:
	up(&data->update_lock);
	return retval;
}

static ssize_t max6875_read(struct kobject *kobj, char *buf, loff_t off, size_t count,
			    enum max6875_area_type area_type)
{
	struct i2c_client *client = to_i2c_client(container_of(kobj, struct device, kobj));
	struct max6875_data *data = i2c_get_clientdata(client);
	struct eeprom_block *blk;
	int slice;

	blk = &data->blocks[area_type];

	if (off > blk->size)
		return 0;
	if (off + count > blk->size)
		count = blk->size - off;

	/* Only refresh slices which contain requested bytes */
	for (slice = (off >> SLICE_BITS); slice <= ((off + count - 1) >> SLICE_BITS); slice++)
		max6875_update_slice(client, blk, slice);

	memcpy(buf, &blk->data[off], count);

	return count;
}

static ssize_t max6875_user_read(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_read(kobj, buf, off, count, max6875_eeprom_user);
}

static ssize_t max6875_config_read(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_read(kobj, buf, off, count, max6875_eeprom_config);
}

static ssize_t max6875_cfgreg_read(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_read(kobj, buf, off, count, max6875_register_config);
}


static ssize_t max6875_write(struct kobject *kobj, char *buf, loff_t off, size_t count,
			     enum max6875_area_type area_type)
{
	struct i2c_client *client = to_i2c_client(container_of(kobj, struct device, kobj));
	struct max6875_data *data = i2c_get_clientdata(client);
	struct eeprom_block *blk;
	int slice, addr, retval;
	ssize_t sent = 0;

	blk = &data->blocks[area_type];

	if (off > blk->size)
		return 0;
	if ((off + count) > blk->size)
		count = blk->size - off;

	if (down_interruptible(&data->update_lock))
		return -EAGAIN;

	/* writing to a register is done with i2c_smbus_write_byte_data() */
	if (blk->type == max6875_register_config) {
		for (sent = 0; sent < count; sent++) {
			addr = off + sent;
			if (addr == 0x44)
				continue;

			retval = i2c_smbus_write_byte_data(client, addr, buf[sent]);
		}
	} else {
		int cmd, val;

		/* We are writing to EEPROM */
		for (sent = 0; sent < count; sent++) {
			addr = blk->base + off + sent;
			cmd = addr >> 8;
			val = (addr & 0xff) | (buf[sent] << 8);	// reversed

			if (addr == 0x8044)
				continue;

			retval = i2c_smbus_write_word_data(client, cmd, val);

			if (retval) {
				goto error_exit;
			}

			/* A write takes up to 11 ms */
			msleep(11);
		}
	}

	/* Invalidate the scratch buffer */
	for (slice = (off >> SLICE_BITS); slice <= ((off + count - 1) >> SLICE_BITS); slice++)
		blk->valid &= ~(1 << slice);

	error_exit:
	up(&data->update_lock);

	return sent;
}

static ssize_t max6875_user_write(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_write(kobj, buf, off, count, max6875_eeprom_user);
}

static ssize_t max6875_config_write(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_write(kobj, buf, off, count, max6875_eeprom_config);
}

static ssize_t max6875_cfgreg_write(struct kobject *kobj, char *buf, loff_t off, size_t count)
{
	return max6875_write(kobj, buf, off, count, max6875_register_config);
}

static struct bin_attribute user_eeprom_attr = {
	.attr = {
		.name = "eeprom_user",
		.mode = S_IRUGO | S_IWUSR | S_IWGRP,
		.owner = THIS_MODULE,
	},
	.size  = USER_EEPROM_SIZE,
	.read  = max6875_user_read,
	.write = max6875_user_write,
};

static struct bin_attribute config_eeprom_attr = {
	.attr = {
		.name = "eeprom_config",
		.mode = S_IRUGO | S_IWUSR,
		.owner = THIS_MODULE,
	},
	.size  = CONFIG_EEPROM_SIZE,
	.read  = max6875_config_read,
	.write = max6875_config_write,
};

static struct bin_attribute config_register_attr = {
	.attr = {
		.name = "reg_config",
		.mode = S_IRUGO | S_IWUSR,
		.owner = THIS_MODULE,
	},
	.size  = CONFIG_EEPROM_SIZE,
	.read  = max6875_cfgreg_read,
	.write = max6875_cfgreg_write,
};

static int max6875_attach_adapter(struct i2c_adapter *adapter)
{
	return i2c_detect(adapter, &addr_data, max6875_detect);
}

/* This function is called by i2c_detect */
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind)
{
	struct i2c_client *new_client;
	struct max6875_data *data;
	int err = 0;

	/* Prevent 24RF08 corruption (in case of user error) */
	if (kind < 0)
		i2c_smbus_xfer(adapter, address, 0, 0, 0,
			       I2C_SMBUS_QUICK, NULL);

	/* There are three ways we can read the EEPROM data:
	   (1) I2C block reads (faster, but unsupported by most adapters)
	   (2) Consecutive byte reads (100% overhead)
	   (3) Regular byte data reads (200% overhead)
	   The third method is not implemented by this driver because all
	   known adapters support at least the second. */
	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_READ_BYTE_DATA |
				     I2C_FUNC_SMBUS_BYTE |
				     I2C_FUNC_SMBUS_WRITE_BYTE_DATA))
		goto exit;

	/* OK. For now, we presume we have a valid client. We now create the
	   client structure, even though we cannot fill it completely yet.
	   But it allows us to access eeprom_{read,write}_value. */
	if (!(data = kmalloc(sizeof(struct max6875_data), GFP_KERNEL))) {
		err = -ENOMEM;
		goto exit;
	}
	memset(data, 0, sizeof(struct max6875_data));

	new_client = &data->client;
	i2c_set_clientdata(new_client, data);
	new_client->addr = address;
	new_client->adapter = adapter;
	new_client->driver = &max6875_driver;
	new_client->flags = 0;

	/* Setup the user section */
	data->blocks[max6875_eeprom_user].type    = max6875_eeprom_user;
	data->blocks[max6875_eeprom_user].slices  = USER_EEPROM_SLICES;
	data->blocks[max6875_eeprom_user].size    = USER_EEPROM_SIZE;
	data->blocks[max6875_eeprom_user].base    = USER_EEPROM_BASE;
	data->blocks[max6875_eeprom_user].data    = data->data;
	data->blocks[max6875_eeprom_user].updated = data->last_updated;

	/* Setup the config section */
	data->blocks[max6875_eeprom_config].type    = max6875_eeprom_config;
	data->blocks[max6875_eeprom_config].slices  = CONFIG_EEPROM_SLICES;
	data->blocks[max6875_eeprom_config].size    = CONFIG_EEPROM_SIZE;
	data->blocks[max6875_eeprom_config].base    = CONFIG_EEPROM_BASE;
	data->blocks[max6875_eeprom_config].data    = &data->data[USER_EEPROM_SIZE];
	data->blocks[max6875_eeprom_config].updated = &data->last_updated[USER_EEPROM_SLICES];

	/* Setup the register section */
	data->blocks[max6875_register_config].type    = max6875_register_config;
	data->blocks[max6875_register_config].slices  = CONFIG_EEPROM_SLICES;
	data->blocks[max6875_register_config].size    = CONFIG_EEPROM_SIZE;
	data->blocks[max6875_register_config].base    = 0;
	data->blocks[max6875_register_config].data    = &data->data[USER_EEPROM_SIZE+CONFIG_EEPROM_SIZE];
	data->blocks[max6875_register_config].updated = &data->last_updated[USER_EEPROM_SLICES+CONFIG_EEPROM_SLICES];

	/* Init the data */
	memset(data->data, 0xff, sizeof(data->data));

	/* Fill in the remaining client fields */
	strlcpy(new_client->name, "max6875", I2C_NAME_SIZE);
	init_MUTEX(&data->update_lock);

	/* Verify that the chip is really what we think it is */
	if ((max6875_update_slice(new_client, &data->blocks[max6875_eeprom_config], 4) < 0) ||
	    (max6875_update_slice(new_client, &data->blocks[max6875_register_config], 4) < 0))
		goto exit_kfree;

	/* 0x41,0x42 must be zero and 0x40 must match in eeprom and registers */
	if ((data->blocks[max6875_eeprom_config].data[0x41] != 0) ||
	    (data->blocks[max6875_eeprom_config].data[0x42] != 0) ||
	    (data->blocks[max6875_register_config].data[0x41] != 0) ||
	    (data->blocks[max6875_register_config].data[0x42] != 0) ||
	    (data->blocks[max6875_eeprom_config].data[0x40] !=
	     data->blocks[max6875_register_config].data[0x40]))
		goto exit_kfree;

	/* Tell the I2C layer a new client has arrived */
	if ((err = i2c_attach_client(new_client)))
		goto exit_kfree;

	/* create the sysfs eeprom files with the correct permissions */
	if (allow_write == 0) {
		user_eeprom_attr.attr.mode &= ~S_IWUGO;
		user_eeprom_attr.write = NULL;
		config_eeprom_attr.attr.mode &= ~S_IWUGO;
		config_eeprom_attr.write = NULL;
		config_register_attr.attr.mode &= ~S_IWUGO;
		config_register_attr.write = NULL;
	}
	sysfs_create_bin_file(&new_client->dev.kobj, &user_eeprom_attr);
	sysfs_create_bin_file(&new_client->dev.kobj, &config_eeprom_attr);
	sysfs_create_bin_file(&new_client->dev.kobj, &config_register_attr);

	return 0;

exit_kfree:
	kfree(data);
exit:
	return err;
}

static int max6875_detach_client(struct i2c_client *client)
{
	int err;

	err = i2c_detach_client(client);
	if (err) {
		dev_err(&client->dev, "Client deregistration failed, client not detached.\n");
		return err;
	}

	kfree(i2c_get_clientdata(client));

	return 0;
}

static int __init max6875_init(void)
{
	return i2c_add_driver(&max6875_driver);
}

static void __exit max6875_exit(void)
{
	i2c_del_driver(&max6875_driver);
}


MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
MODULE_DESCRIPTION("MAX6875 driver");
MODULE_LICENSE("GPL");

module_init(max6875_init);
module_exit(max6875_exit);