/*
 *  ads7871 - driver for TI ADS7871 A/D converter
 *
 *  Copyright (c) 2010 Paul Thomas <pthomas8589@gmail.com>
 *
 *  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.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 or
 *  later as publishhed by the Free Software Foundation.
 *
 *      You need to have something like this in struct spi_board_info
 *      {
 *              .modalias       = "ads7871",
 *              .max_speed_hz   = 2*1000*1000,
 *              .chip_select    = 0,
 *              .bus_num        = 1,
 *      },
 */

/*From figure 18 in the datasheet*/
/*Register addresses*/
#define REG_LS_BYTE     0 /*A/D Output Data, LS Byte*/
#define REG_MS_BYTE     1 /*A/D Output Data, MS Byte*/
#define REG_PGA_VALID   2 /*PGA Valid Register*/
#define REG_AD_CONTROL  3 /*A/D Control Register*/
#define REG_GAIN_MUX    4 /*Gain/Mux Register*/
#define REG_IO_STATE    5 /*Digital I/O State Register*/
#define REG_IO_CONTROL  6 /*Digital I/O Control Register*/
#define REG_OSC_CONTROL 7 /*Rev/Oscillator Control Register*/
#define REG_SER_CONTROL 24 /*Serial Interface Control Register*/
#define REG_ID          31 /*ID Register*/

/*
 * From figure 17 in the datasheet
 * These bits get ORed with the address to form
 * the instruction byte
 */
/*Instruction Bit masks*/
#define INST_MODE_BM    (1 << 7)
#define INST_READ_BM    (1 << 6)
#define INST_16BIT_BM   (1 << 5)

/*From figure 18 in the datasheet*/
/*bit masks for Rev/Oscillator Control Register*/
#define MUX_CNV_BV      7
#define MUX_CNV_BM      (1 << MUX_CNV_BV)
#define MUX_M3_BM       (1 << 3) /*M3 selects single ended*/
#define MUX_G_BV        4 /*allows for reg = (gain << MUX_G_BV) | ...*/

/*From figure 18 in the datasheet*/
/*bit masks for Rev/Oscillator Control Register*/
#define OSC_OSCR_BM     (1 << 5)
#define OSC_OSCE_BM     (1 << 4)
#define OSC_REFE_BM     (1 << 3)
#define OSC_BUFE_BM     (1 << 2)
#define OSC_R2V_BM      (1 << 1)
#define OSC_RBG_BM      (1 << 0)

#include <linux/module.h>
#include <linux/init.h>
#include <linux/spi/spi.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/delay.h>

#define DEVICE_NAME     "ads7871"

struct ads7871_data {
        struct device   *hwmon_dev;
        struct mutex    update_lock;
};

static int ads7871_read_reg8(struct spi_device *spi, int reg)
{
        int ret;
        reg = reg | INST_READ_BM;
        ret = spi_w8r8(spi, reg);
        return ret;
}

static int ads7871_read_reg16(struct spi_device *spi, int reg)
{
        int ret;
        reg = reg | INST_READ_BM | INST_16BIT_BM;
        ret = spi_w8r16(spi, reg);
        return ret;
}

static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val)
{
        u8 tmp[2] = {reg, val};
        return spi_write(spi, tmp, sizeof(tmp));
}

static ssize_t show_voltage(struct device *dev,
                struct device_attribute *da, char *buf)
{
        struct spi_device *spi = to_spi_device(dev);
        struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
        int ret, val, i = 0;
        uint8_t channel, mux_cnv;

        channel = attr->index;
        /*
         * TODO: add support for conversions
         * other than single ended with a gain of 1
         */
        /*MUX_M3_BM forces single ended*/
        /*This is also where the gain of the PGA would be set*/
        ads7871_write_reg8(spi, REG_GAIN_MUX,
                (MUX_CNV_BM | MUX_M3_BM | channel));

        ret = ads7871_read_reg8(spi, REG_GAIN_MUX);
        mux_cnv = ((ret & MUX_CNV_BM) >> MUX_CNV_BV);
        /*
         * on 400MHz arm9 platform the conversion
         * is already done when we do this test
         */
        while ((i < 2) && mux_cnv) {
                i++;
                ret = ads7871_read_reg8(spi, REG_GAIN_MUX);
                mux_cnv = ((ret & MUX_CNV_BM) >> MUX_CNV_BV);
                msleep_interruptible(1);
        }

        if (mux_cnv == 0) {
                val = ads7871_read_reg16(spi, REG_LS_BYTE);
                /*result in volts*10000 = (val/8192)*2.5*10000*/
                val = ((val >> 2) * 25000) / 8192;
                return sprintf(buf, "%d\n", val);
        } else {
                return -1;
        }
}

static ssize_t ads7871_show_name(struct device *dev,
                                 struct device_attribute *devattr, char *buf)
{
        return sprintf(buf, "%s\n", to_spi_device(dev)->modalias);
}

static SENSOR_DEVICE_ATTR(in0_input, S_IRUGO, show_voltage, NULL, 0);
static SENSOR_DEVICE_ATTR(in1_input, S_IRUGO, show_voltage, NULL, 1);
static SENSOR_DEVICE_ATTR(in2_input, S_IRUGO, show_voltage, NULL, 2);
static SENSOR_DEVICE_ATTR(in3_input, S_IRUGO, show_voltage, NULL, 3);
static SENSOR_DEVICE_ATTR(in4_input, S_IRUGO, show_voltage, NULL, 4);
static SENSOR_DEVICE_ATTR(in5_input, S_IRUGO, show_voltage, NULL, 5);
static SENSOR_DEVICE_ATTR(in6_input, S_IRUGO, show_voltage, NULL, 6);
static SENSOR_DEVICE_ATTR(in7_input, S_IRUGO, show_voltage, NULL, 7);

static DEVICE_ATTR(name, S_IRUGO, ads7871_show_name, NULL);

static struct attribute *ads7871_attributes[] = {
        &sensor_dev_attr_in0_input.dev_attr.attr,
        &sensor_dev_attr_in1_input.dev_attr.attr,
        &sensor_dev_attr_in2_input.dev_attr.attr,
        &sensor_dev_attr_in3_input.dev_attr.attr,
        &sensor_dev_attr_in4_input.dev_attr.attr,
        &sensor_dev_attr_in5_input.dev_attr.attr,
        &sensor_dev_attr_in6_input.dev_attr.attr,
        &sensor_dev_attr_in7_input.dev_attr.attr,
        &dev_attr_name.attr,
        NULL
};

static const struct attribute_group ads7871_group = {
        .attrs = ads7871_attributes,
};

static int ads7871_probe(struct spi_device *spi)
{
        int ret, err;
        uint8_t val;
        struct ads7871_data *pdata;

        dev_dbg(&spi->dev, "probe\n");

        /* Configure the SPI bus */
        spi->mode = (SPI_MODE_0);
        spi->bits_per_word = 8;
        spi_setup(spi);

        ads7871_write_reg8(spi, REG_SER_CONTROL, 0);
        ads7871_write_reg8(spi, REG_AD_CONTROL, 0);

        val = (OSC_OSCR_BM | OSC_OSCE_BM | OSC_REFE_BM | OSC_BUFE_BM);
        ads7871_write_reg8(spi, REG_OSC_CONTROL, val);
        ret = ads7871_read_reg8(spi, REG_OSC_CONTROL);

        dev_dbg(&spi->dev, "REG_OSC_CONTROL write:%x, read:%x\n", val, ret);
        /*
         * because there is no other error checking on an SPI bus
         * we need to make sure we really have a chip
         */
        if (val != ret)
                return -ENODEV;

        pdata = devm_kzalloc(&spi->dev, sizeof(struct ads7871_data),
                             GFP_KERNEL);
        if (!pdata)
                return -ENOMEM;

        err = sysfs_create_group(&spi->dev.kobj, &ads7871_group);
        if (err < 0)
                return err;

        spi_set_drvdata(spi, pdata);

        pdata->hwmon_dev = hwmon_device_register(&spi->dev);
        if (IS_ERR(pdata->hwmon_dev)) {
                err = PTR_ERR(pdata->hwmon_dev);
                goto error_remove;
        }

        return 0;

error_remove:
        sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
        return err;
}

static int ads7871_remove(struct spi_device *spi)
{
        struct ads7871_data *pdata = spi_get_drvdata(spi);

        hwmon_device_unregister(pdata->hwmon_dev);
        sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
        return 0;
}

static struct spi_driver ads7871_driver = {
        .driver = {
                .name = DEVICE_NAME,
        },

        .probe = ads7871_probe,
        .remove = ads7871_remove,
};

module_spi_driver(ads7871_driver);

MODULE_AUTHOR("Paul Thomas <pthomas8589@gmail.com>");
MODULE_DESCRIPTION("TI ADS7871 A/D driver");
MODULE_LICENSE("GPL");