/*
 * CBUS I2C driver for Nokia Internet Tablets.
 *
 * Copyright (C) 2004-2010 Nokia Corporation
 *
 * Based on code written by Juha Yrjölä, David Weinehall, Mikko Ylinen and
 * Felipe Balbi. Converted to I2C driver by Aaro Koskinen.
 *
 * This file is subject to the terms and conditions of the GNU General
 * Public License. See the file "COPYING" in the main directory of this
 * archive for more details.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 */

#include <linux/io.h>
#include <linux/i2c.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/gpio/consumer.h>
#include <linux/interrupt.h>
#include <linux/platform_device.h>

/*
 * Bit counts are derived from Nokia implementation. These should be checked
 * if other CBUS implementations appear.
 */
#define CBUS_ADDR_BITS  3
#define CBUS_REG_BITS   5

struct cbus_host {
        spinlock_t      lock;           /* host lock */
        struct device   *dev;
        struct gpio_desc *clk;
        struct gpio_desc *dat;
        struct gpio_desc *sel;
};

/**
 * cbus_send_bit - sends one bit over the bus
 * @host: the host we're using
 * @bit: one bit of information to send
 */
static void cbus_send_bit(struct cbus_host *host, unsigned bit)
{
        gpiod_set_value(host->dat, bit ? 1 : 0);
        gpiod_set_value(host->clk, 1);
        gpiod_set_value(host->clk, 0);
}

/**
 * cbus_send_data - sends @len amount of data over the bus
 * @host: the host we're using
 * @data: the data to send
 * @len: size of the transfer
 */
static void cbus_send_data(struct cbus_host *host, unsigned data, unsigned len)
{
        int i;

        for (i = len; i > 0; i--)
                cbus_send_bit(host, data & (1 << (i - 1)));
}

/**
 * cbus_receive_bit - receives one bit from the bus
 * @host: the host we're using
 */
static int cbus_receive_bit(struct cbus_host *host)
{
        int ret;

        gpiod_set_value(host->clk, 1);
        ret = gpiod_get_value(host->dat);
        gpiod_set_value(host->clk, 0);
        return ret;
}

/**
 * cbus_receive_word - receives 16-bit word from the bus
 * @host: the host we're using
 */
static int cbus_receive_word(struct cbus_host *host)
{
        int ret = 0;
        int i;

        for (i = 16; i > 0; i--) {
                int bit = cbus_receive_bit(host);

                if (bit < 0)
                        return bit;

                if (bit)
                        ret |= 1 << (i - 1);
        }
        return ret;
}

/**
 * cbus_transfer - transfers data over the bus
 * @host: the host we're using
 * @rw: read/write flag
 * @dev: device address
 * @reg: register address
 * @data: if @rw == I2C_SBUS_WRITE data to send otherwise 0
 */
static int cbus_transfer(struct cbus_host *host, char rw, unsigned dev,
                         unsigned reg, unsigned data)
{
        unsigned long flags;
        int ret;

        /* We don't want interrupts disturbing our transfer */
        spin_lock_irqsave(&host->lock, flags);

        /* Reset state and start of transfer, SEL stays down during transfer */
        gpiod_set_value(host->sel, 0);

        /* Set the DAT pin to output */
        gpiod_direction_output(host->dat, 1);

        /* Send the device address */
        cbus_send_data(host, dev, CBUS_ADDR_BITS);

        /* Send the rw flag */
        cbus_send_bit(host, rw == I2C_SMBUS_READ);

        /* Send the register address */
        cbus_send_data(host, reg, CBUS_REG_BITS);

        if (rw == I2C_SMBUS_WRITE) {
                cbus_send_data(host, data, 16);
                ret = 0;
        } else {
                ret = gpiod_direction_input(host->dat);
                if (ret) {
                        dev_dbg(host->dev, "failed setting direction\n");
                        goto out;
                }
                gpiod_set_value(host->clk, 1);

                ret = cbus_receive_word(host);
                if (ret < 0) {
                        dev_dbg(host->dev, "failed receiving data\n");
                        goto out;
                }
        }

        /* Indicate end of transfer, SEL goes up until next transfer */
        gpiod_set_value(host->sel, 1);
        gpiod_set_value(host->clk, 1);
        gpiod_set_value(host->clk, 0);

out:
        spin_unlock_irqrestore(&host->lock, flags);

        return ret;
}

static int cbus_i2c_smbus_xfer(struct i2c_adapter       *adapter,
                               u16                      addr,
                               unsigned short           flags,
                               char                     read_write,
                               u8                       command,
                               int                      size,
                               union i2c_smbus_data     *data)
{
        struct cbus_host *chost = i2c_get_adapdata(adapter);
        int ret;

        if (size != I2C_SMBUS_WORD_DATA)
                return -EINVAL;

        ret = cbus_transfer(chost, read_write == I2C_SMBUS_READ, addr,
                            command, data->word);
        if (ret < 0)
                return ret;

        if (read_write == I2C_SMBUS_READ)
                data->word = ret;

        return 0;
}

static u32 cbus_i2c_func(struct i2c_adapter *adapter)
{
        return I2C_FUNC_SMBUS_READ_WORD_DATA | I2C_FUNC_SMBUS_WRITE_WORD_DATA;
}

static const struct i2c_algorithm cbus_i2c_algo = {
        .smbus_xfer             = cbus_i2c_smbus_xfer,
        .smbus_xfer_atomic      = cbus_i2c_smbus_xfer,
        .functionality          = cbus_i2c_func,
};

static void cbus_i2c_remove(struct platform_device *pdev)
{
        struct i2c_adapter *adapter = platform_get_drvdata(pdev);

        i2c_del_adapter(adapter);
}

static int cbus_i2c_probe(struct platform_device *pdev)
{
        struct i2c_adapter *adapter;
        struct cbus_host *chost;

        adapter = devm_kzalloc(&pdev->dev, sizeof(struct i2c_adapter),
                               GFP_KERNEL);
        if (!adapter)
                return -ENOMEM;

        chost = devm_kzalloc(&pdev->dev, sizeof(*chost), GFP_KERNEL);
        if (!chost)
                return -ENOMEM;

        if (gpiod_count(&pdev->dev, NULL) != 3)
                return -ENODEV;
        chost->clk = devm_gpiod_get_index(&pdev->dev, NULL, 0, GPIOD_OUT_LOW);
        if (IS_ERR(chost->clk))
                return PTR_ERR(chost->clk);
        chost->dat = devm_gpiod_get_index(&pdev->dev, NULL, 1, GPIOD_IN);
        if (IS_ERR(chost->dat))
                return PTR_ERR(chost->dat);
        chost->sel = devm_gpiod_get_index(&pdev->dev, NULL, 2, GPIOD_OUT_HIGH);
        if (IS_ERR(chost->sel))
                return PTR_ERR(chost->sel);
        gpiod_set_consumer_name(chost->clk, "CBUS clk");
        gpiod_set_consumer_name(chost->dat, "CBUS dat");
        gpiod_set_consumer_name(chost->sel, "CBUS sel");

        adapter->owner          = THIS_MODULE;
        adapter->class          = I2C_CLASS_HWMON;
        adapter->dev.parent     = &pdev->dev;
        adapter->dev.of_node    = pdev->dev.of_node;
        adapter->nr             = pdev->id;
        adapter->timeout        = HZ;
        adapter->algo           = &cbus_i2c_algo;
        strscpy(adapter->name, "CBUS I2C adapter", sizeof(adapter->name));

        spin_lock_init(&chost->lock);
        chost->dev = &pdev->dev;

        i2c_set_adapdata(adapter, chost);
        platform_set_drvdata(pdev, adapter);

        return i2c_add_numbered_adapter(adapter);
}

#if defined(CONFIG_OF)
static const struct of_device_id i2c_cbus_dt_ids[] = {
        { .compatible = "i2c-cbus-gpio", },
        { }
};
MODULE_DEVICE_TABLE(of, i2c_cbus_dt_ids);
#endif

static struct platform_driver cbus_i2c_driver = {
        .probe  = cbus_i2c_probe,
        .remove = cbus_i2c_remove,
        .driver = {
                .name   = "i2c-cbus-gpio",
                .of_match_table = of_match_ptr(i2c_cbus_dt_ids),
        },
};
module_platform_driver(cbus_i2c_driver);

MODULE_ALIAS("platform:i2c-cbus-gpio");
MODULE_DESCRIPTION("CBUS I2C driver");
MODULE_AUTHOR("Juha Yrjölä");
MODULE_AUTHOR("David Weinehall");
MODULE_AUTHOR("Mikko Ylinen");
MODULE_AUTHOR("Felipe Balbi");
MODULE_AUTHOR("Aaro Koskinen <aaro.koskinen@iki.fi>");
MODULE_LICENSE("GPL");