// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  ads7871 - driver for TI ADS7871 A/D converter
 *
 *  Copyright (c) 2010 Paul Thomas <pthomas8589@gmail.com>
 *
 *	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/err.h>
#include <linux/delay.h>

#define DEVICE_NAME	"ads7871"

struct ads7871_data {
	struct spi_device *spi;
	u8 tx_buf[2] ____cacheline_aligned;
};

static umode_t ads7871_is_visible(const void *data,
				  enum hwmon_sensor_types type,
				  u32 attr, int channel)
{
	if (type == hwmon_in && attr == hwmon_in_input)
		return 0444;

	return 0;
}

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);
	if (ret < 0)
		return ret;

	return le16_to_cpu((__force __le16)ret);
}

static int ads7871_write_reg8(struct ads7871_data *pdata, int reg, u8 val)
{
	pdata->tx_buf[0] = reg;
	pdata->tx_buf[1] = val;

	return spi_write(pdata->spi, pdata->tx_buf, 2);
}

static int ads7871_read(struct device *dev, enum hwmon_sensor_types type,
			u32 attr, int channel, long *val)
{
	struct ads7871_data *pdata = dev_get_drvdata(dev);
	struct spi_device *spi = pdata->spi;
	int ret, raw_val, i = 0;
	u8 mux_cnv;

	if (type != hwmon_in || attr != hwmon_in_input)
		return -EOPNOTSUPP;
	/*
	 * 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*/
	ret = ads7871_write_reg8(pdata, REG_GAIN_MUX,
				 (MUX_CNV_BM | MUX_M3_BM | channel));
	if (ret < 0)
		return ret;

	ret = ads7871_read_reg8(spi, REG_GAIN_MUX);
	if (ret < 0)
		return ret;

	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);
		if (ret < 0)
			return ret;
		mux_cnv = ((ret & MUX_CNV_BM) >> MUX_CNV_BV);
		msleep_interruptible(1);
	}

	if (mux_cnv == 0) {
		raw_val = ads7871_read_reg16(spi, REG_LS_BYTE);
		if (raw_val < 0)
			return raw_val;

		/*
		 * Use (s16) to ensure the sign bit is preserved during the shift.
		 * Report millivolts (2.5V = 2500mV).
		 */
		*val = ((s16)raw_val >> 2) * 2500 / 8192;
		return 0;
	}

	return -ETIMEDOUT;
}

static const struct hwmon_channel_info * const ads7871_info[] = {
	HWMON_CHANNEL_INFO(in,
			   HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT,
			   HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT, HWMON_I_INPUT),
	NULL
};

static const struct hwmon_ops ads7871_hwmon_ops = {
	.is_visible = ads7871_is_visible,
	.read = ads7871_read,
};

static const struct hwmon_chip_info ads7871_chip_info = {
	.ops = &ads7871_hwmon_ops,
	.info = ads7871_info,
};

static int ads7871_probe(struct spi_device *spi)
{
	struct device *dev = &spi->dev;
	int ret;
	uint8_t val;
	struct ads7871_data *pdata;
	struct device *hwmon_dev;

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

	pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
	if (!pdata)
		return -ENOMEM;

	pdata->spi = spi;

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

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

	dev_dbg(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;

	hwmon_dev = devm_hwmon_device_register_with_info(dev, spi->modalias,
							 pdata,
							 &ads7871_chip_info,
							 NULL);
	return PTR_ERR_OR_ZERO(hwmon_dev);
}

static struct spi_driver ads7871_driver = {
	.driver = {
		.name = DEVICE_NAME,
	},
	.probe = ads7871_probe,
};

module_spi_driver(ads7871_driver);

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