ads7871.c

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/*
 *  ads7871 - driver for TI ADS7871 A/D converter
 *
 *  Copyright (c) 2010 Paul Thomas <[email protected]>
 *
 *  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 __devinit 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 __devexit 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,
        .owner = THIS_MODULE,
    },

    .probe = ads7871_probe,
    .remove = __devexit_p(ads7871_remove),
};

module_spi_driver(ads7871_driver);

MODULE_AUTHOR("Paul Thomas <[email protected]>");
MODULE_DESCRIPTION("TI ADS7871 A/D driver");
MODULE_LICENSE("GPL");