drm/client: Fix drm client endless Kconfig loop

[drm/drm-misc.git] / drivers / iio / adc / ti-ads1298.c

// SPDX-License-Identifier: GPL-2.0
/* TI ADS1298 chip family driver
 * Copyright (C) 2023 - 2024 Topic Embedded Products
 */

#include <linux/bitfield.h>
#include <linux/cleanup.h>
#include <linux/clk.h>
#include <linux/err.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/gpio/consumer.h>
#include <linux/log2.h>
#include <linux/math.h>
#include <linux/module.h>
#include <linux/regmap.h>
#include <linux/regulator/consumer.h>
#include <linux/slab.h>
#include <linux/spi/spi.h>
#include <linux/units.h>

#include <linux/iio/iio.h>
#include <linux/iio/buffer.h>
#include <linux/iio/kfifo_buf.h>

#include <linux/unaligned.h>

/* Commands */
#define ADS1298_CMD_WAKEUP      0x02
#define ADS1298_CMD_STANDBY     0x04
#define ADS1298_CMD_RESET       0x06
#define ADS1298_CMD_START       0x08
#define ADS1298_CMD_STOP        0x0a
#define ADS1298_CMD_RDATAC      0x10
#define ADS1298_CMD_SDATAC      0x11
#define ADS1298_CMD_RDATA       0x12
#define ADS1298_CMD_RREG        0x20
#define ADS1298_CMD_WREG        0x40

/* Registers */
#define ADS1298_REG_ID          0x00
#define ADS1298_MASK_ID_FAMILY                  GENMASK(7, 3)
#define ADS1298_MASK_ID_CHANNELS                GENMASK(2, 0)
#define ADS1298_ID_FAMILY_ADS129X               0x90
#define ADS1298_ID_FAMILY_ADS129XR              0xd0

#define ADS1298_REG_CONFIG1     0x01
#define ADS1298_MASK_CONFIG1_HR                 BIT(7)
#define ADS1298_MASK_CONFIG1_DR                 GENMASK(2, 0)
#define ADS1298_SHIFT_DR_HR                     6
#define ADS1298_SHIFT_DR_LP                     7
#define ADS1298_LOWEST_DR                       0x06

#define ADS1298_REG_CONFIG2     0x02
#define ADS1298_MASK_CONFIG2_RESERVED           BIT(6)
#define ADS1298_MASK_CONFIG2_WCT_CHOP           BIT(5)
#define ADS1298_MASK_CONFIG2_INT_TEST           BIT(4)
#define ADS1298_MASK_CONFIG2_TEST_AMP           BIT(2)
#define ADS1298_MASK_CONFIG2_TEST_FREQ_DC       GENMASK(1, 0)
#define ADS1298_MASK_CONFIG2_TEST_FREQ_SLOW     0
#define ADS1298_MASK_CONFIG2_TEST_FREQ_FAST     BIT(0)

#define ADS1298_REG_CONFIG3     0x03
#define ADS1298_MASK_CONFIG3_PWR_REFBUF         BIT(7)
#define ADS1298_MASK_CONFIG3_RESERVED           BIT(6)
#define ADS1298_MASK_CONFIG3_VREF_4V            BIT(5)

#define ADS1298_REG_LOFF        0x04
#define ADS1298_REG_CHnSET(n)   (0x05 + n)
#define ADS1298_MASK_CH_PD              BIT(7)
#define ADS1298_MASK_CH_PGA             GENMASK(6, 4)
#define ADS1298_MASK_CH_MUX             GENMASK(2, 0)

#define ADS1298_REG_LOFF_STATP  0x12
#define ADS1298_REG_LOFF_STATN  0x13
#define ADS1298_REG_CONFIG4     0x17
#define ADS1298_MASK_CONFIG4_SINGLE_SHOT        BIT(3)

#define ADS1298_REG_WCT1        0x18
#define ADS1298_REG_WCT2        0x19

#define ADS1298_MAX_CHANNELS    8
#define ADS1298_BITS_PER_SAMPLE 24
#define ADS1298_CLK_RATE_HZ     2048000
#define ADS1298_CLOCKS_TO_USECS(x) \
                (DIV_ROUND_UP((x) * MICROHZ_PER_HZ, ADS1298_CLK_RATE_HZ))
/*
 * Read/write register commands require 4 clocks to decode, for speeds above
 * 2x the clock rate, this would require extra time between the command byte and
 * the data. Much simpler is to just limit the SPI transfer speed while doing
 * register access.
 */
#define ADS1298_SPI_BUS_SPEED_SLOW      ADS1298_CLK_RATE_HZ
/* For reading and writing registers, we need a 3-byte buffer */
#define ADS1298_SPI_CMD_BUFFER_SIZE     3
/* Outputs status word and 'n' 24-bit samples, plus the command byte */
#define ADS1298_SPI_RDATA_BUFFER_SIZE(n)        (((n) + 1) * 3 + 1)
#define ADS1298_SPI_RDATA_BUFFER_SIZE_MAX \
                ADS1298_SPI_RDATA_BUFFER_SIZE(ADS1298_MAX_CHANNELS)

struct ads1298_private {
        const struct ads1298_chip_info *chip_info;
        struct spi_device *spi;
        struct regulator *reg_avdd;
        struct regulator *reg_vref;
        struct clk *clk;
        struct regmap *regmap;
        struct completion completion;
        struct iio_trigger *trig;
        struct spi_transfer rdata_xfer;
        struct spi_message rdata_msg;
        spinlock_t irq_busy_lock; /* Handshake between SPI and DRDY irqs */
        /*
         * rdata_xfer_busy increments when a DRDY occurs and decrements when SPI
         * completion is reported. Hence its meaning is:
         * 0 = Waiting for DRDY interrupt
         * 1 = SPI transfer in progress
         * 2 = DRDY during SPI transfer, start another transfer on completion
         * >2 = Multiple DRDY during transfer, lost rdata_xfer_busy - 2 samples
         */
        unsigned int rdata_xfer_busy;

        /* Temporary storage for demuxing data after SPI transfer */
        u32 bounce_buffer[ADS1298_MAX_CHANNELS];

        /* For synchronous SPI exchanges (read/write registers) */
        u8 cmd_buffer[ADS1298_SPI_CMD_BUFFER_SIZE] __aligned(IIO_DMA_MINALIGN);

        /* Buffer used for incoming SPI data */
        u8 rx_buffer[ADS1298_SPI_RDATA_BUFFER_SIZE_MAX];
        /* Contains the RDATA command and zeroes to clock out */
        u8 tx_buffer[ADS1298_SPI_RDATA_BUFFER_SIZE_MAX];
};

/* Three bytes per sample in RX buffer, starting at offset 4 */
#define ADS1298_OFFSET_IN_RX_BUFFER(index)      (3 * (index) + 4)

#define ADS1298_CHAN(index)                             \
{                                                       \
        .type = IIO_VOLTAGE,                            \
        .indexed = 1,                                   \
        .channel = index,                               \
        .address = ADS1298_OFFSET_IN_RX_BUFFER(index),  \
        .info_mask_separate =                           \
                BIT(IIO_CHAN_INFO_RAW) |                \
                BIT(IIO_CHAN_INFO_SCALE),               \
        .info_mask_shared_by_all =                      \
                BIT(IIO_CHAN_INFO_SAMP_FREQ) |          \
                BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),  \
        .scan_index = index,                            \
        .scan_type = {                                  \
                .sign = 's',                            \
                .realbits = ADS1298_BITS_PER_SAMPLE,    \
                .storagebits = 32,                      \
                .endianness = IIO_CPU,                  \
        },                                              \
}

static const struct iio_chan_spec ads1298_channels[] = {
        ADS1298_CHAN(0),
        ADS1298_CHAN(1),
        ADS1298_CHAN(2),
        ADS1298_CHAN(3),
        ADS1298_CHAN(4),
        ADS1298_CHAN(5),
        ADS1298_CHAN(6),
        ADS1298_CHAN(7),
};

static int ads1298_write_cmd(struct ads1298_private *priv, u8 command)
{
        struct spi_transfer xfer = {
                .tx_buf = priv->cmd_buffer,
                .rx_buf = priv->cmd_buffer,
                .len = 1,
                .speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
                .delay = {
                        .value = 2,
                        .unit = SPI_DELAY_UNIT_USECS,
                },
        };

        priv->cmd_buffer[0] = command;

        return spi_sync_transfer(priv->spi, &xfer, 1);
}

static int ads1298_read_one(struct ads1298_private *priv, int chan_index)
{
        int ret;

        /* Enable the channel */
        ret = regmap_update_bits(priv->regmap, ADS1298_REG_CHnSET(chan_index),
                                 ADS1298_MASK_CH_PD, 0);
        if (ret)
                return ret;

        /* Enable single-shot mode, so we don't need to send a STOP */
        ret = regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG4,
                                 ADS1298_MASK_CONFIG4_SINGLE_SHOT,
                                 ADS1298_MASK_CONFIG4_SINGLE_SHOT);
        if (ret)
                return ret;

        reinit_completion(&priv->completion);

        ret = ads1298_write_cmd(priv, ADS1298_CMD_START);
        if (ret < 0) {
                dev_err(&priv->spi->dev, "CMD_START error: %d\n", ret);
                return ret;
        }

        /* Cannot take longer than 40ms (250Hz) */
        ret = wait_for_completion_timeout(&priv->completion, msecs_to_jiffies(50));
        if (!ret)
                return -ETIMEDOUT;

        return 0;
}

static int ads1298_get_samp_freq(struct ads1298_private *priv, int *val)
{
        unsigned long rate;
        unsigned int cfg;
        int ret;

        ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG1, &cfg);
        if (ret)
                return ret;

        if (priv->clk)
                rate = clk_get_rate(priv->clk);
        else
                rate = ADS1298_CLK_RATE_HZ;
        if (!rate)
                return -EINVAL;

        /* Data rate shift depends on HR/LP mode */
        if (cfg & ADS1298_MASK_CONFIG1_HR)
                rate >>= ADS1298_SHIFT_DR_HR;
        else
                rate >>= ADS1298_SHIFT_DR_LP;

        *val = rate >> (cfg & ADS1298_MASK_CONFIG1_DR);

        return IIO_VAL_INT;
}

static int ads1298_set_samp_freq(struct ads1298_private *priv, int val)
{
        unsigned long rate;
        unsigned int factor;
        unsigned int cfg;

        if (priv->clk)
                rate = clk_get_rate(priv->clk);
        else
                rate = ADS1298_CLK_RATE_HZ;
        if (!rate)
                return -EINVAL;
        if (val <= 0)
                return -EINVAL;

        factor = (rate >> ADS1298_SHIFT_DR_HR) / val;
        if (factor >= BIT(ADS1298_SHIFT_DR_LP))
                cfg = ADS1298_LOWEST_DR;
        else if (factor)
                cfg = ADS1298_MASK_CONFIG1_HR | ilog2(factor); /* Use HR mode */
        else
                cfg = ADS1298_MASK_CONFIG1_HR; /* Fastest possible */

        return regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG1,
                                  ADS1298_MASK_CONFIG1_HR | ADS1298_MASK_CONFIG1_DR,
                                  cfg);
}

static const u8 ads1298_pga_settings[] = { 6, 1, 2, 3, 4, 8, 12 };

static int ads1298_get_scale(struct ads1298_private *priv,
                             int channel, int *val, int *val2)
{
        int ret;
        unsigned int regval;
        u8 gain;

        if (priv->reg_vref) {
                ret = regulator_get_voltage(priv->reg_vref);
                if (ret < 0)
                        return ret;

                *val = ret / MILLI; /* Convert to millivolts */
        } else {
                ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG3, &regval);
                if (ret)
                        return ret;

                /* Reference in millivolts */
                *val = regval & ADS1298_MASK_CONFIG3_VREF_4V ? 4000 : 2400;
        }

        ret = regmap_read(priv->regmap, ADS1298_REG_CHnSET(channel), &regval);
        if (ret)
                return ret;

        gain = ads1298_pga_settings[FIELD_GET(ADS1298_MASK_CH_PGA, regval)];
        *val /= gain; /* Full scale is VREF / gain */

        *val2 = ADS1298_BITS_PER_SAMPLE - 1; /* Signed, hence the -1 */

        return IIO_VAL_FRACTIONAL_LOG2;
}

static int ads1298_read_raw(struct iio_dev *indio_dev,
                            struct iio_chan_spec const *chan,
                            int *val, int *val2, long mask)
{
        struct ads1298_private *priv = iio_priv(indio_dev);
        int ret;

        switch (mask) {
        case IIO_CHAN_INFO_RAW:
                ret = iio_device_claim_direct_mode(indio_dev);
                if (ret)
                        return ret;

                ret = ads1298_read_one(priv, chan->scan_index);

                iio_device_release_direct_mode(indio_dev);

                if (ret)
                        return ret;

                *val = sign_extend32(get_unaligned_be24(priv->rx_buffer + chan->address),
                                     ADS1298_BITS_PER_SAMPLE - 1);
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                return ads1298_get_scale(priv, chan->channel, val, val2);
        case IIO_CHAN_INFO_SAMP_FREQ:
                return ads1298_get_samp_freq(priv, val);
        case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
                ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG1, val);
                if (ret)
                        return ret;

                *val = 16 << (*val & ADS1298_MASK_CONFIG1_DR);
                return IIO_VAL_INT;
        default:
                return -EINVAL;
        }
}

static int ads1298_write_raw(struct iio_dev *indio_dev,
                             struct iio_chan_spec const *chan, int val,
                             int val2, long mask)
{
        struct ads1298_private *priv = iio_priv(indio_dev);

        switch (mask) {
        case IIO_CHAN_INFO_SAMP_FREQ:
                return ads1298_set_samp_freq(priv, val);
        default:
                return -EINVAL;
        }
}

static int ads1298_reg_write(void *context, unsigned int reg, unsigned int val)
{
        struct ads1298_private *priv = context;
        struct spi_transfer reg_write_xfer = {
                .tx_buf = priv->cmd_buffer,
                .rx_buf = priv->cmd_buffer,
                .len = 3,
                .speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
                .delay = {
                        .value = 2,
                        .unit = SPI_DELAY_UNIT_USECS,
                },
        };

        priv->cmd_buffer[0] = ADS1298_CMD_WREG | reg;
        priv->cmd_buffer[1] = 0; /* Number of registers to be written - 1 */
        priv->cmd_buffer[2] = val;

        return spi_sync_transfer(priv->spi, &reg_write_xfer, 1);
}

static int ads1298_reg_read(void *context, unsigned int reg, unsigned int *val)
{
        struct ads1298_private *priv = context;
        struct spi_transfer reg_read_xfer = {
                .tx_buf = priv->cmd_buffer,
                .rx_buf = priv->cmd_buffer,
                .len = 3,
                .speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
                .delay = {
                        .value = 2,
                        .unit = SPI_DELAY_UNIT_USECS,
                },
        };
        int ret;

        priv->cmd_buffer[0] = ADS1298_CMD_RREG | reg;
        priv->cmd_buffer[1] = 0; /* Number of registers to be read - 1 */
        priv->cmd_buffer[2] = 0;

        ret = spi_sync_transfer(priv->spi, &reg_read_xfer, 1);
        if (ret)
                return ret;

        *val = priv->cmd_buffer[2];

        return 0;
}

static int ads1298_reg_access(struct iio_dev *indio_dev, unsigned int reg,
                              unsigned int writeval, unsigned int *readval)
{
        struct ads1298_private *priv = iio_priv(indio_dev);

        if (readval)
                return regmap_read(priv->regmap, reg, readval);

        return regmap_write(priv->regmap, reg, writeval);
}

static void ads1298_rdata_unmark_busy(struct ads1298_private *priv)
{
        /* Notify we're no longer waiting for the SPI transfer to complete */
        guard(spinlock_irqsave)(&priv->irq_busy_lock);
        priv->rdata_xfer_busy = 0;
}

static int ads1298_update_scan_mode(struct iio_dev *indio_dev,
                                    const unsigned long *scan_mask)
{
        struct ads1298_private *priv = iio_priv(indio_dev);
        unsigned int val;
        int ret;
        int i;

        /* Make the interrupt routines start with a clean slate */
        ads1298_rdata_unmark_busy(priv);

        /* Configure power-down bits to match scan mask */
        for (i = 0; i < indio_dev->num_channels; i++) {
                val = test_bit(i, scan_mask) ? 0 : ADS1298_MASK_CH_PD;
                ret = regmap_update_bits(priv->regmap, ADS1298_REG_CHnSET(i),
                                         ADS1298_MASK_CH_PD, val);
                if (ret)
                        return ret;
        }

        return 0;
}

static const struct iio_info ads1298_info = {
        .read_raw = &ads1298_read_raw,
        .write_raw = &ads1298_write_raw,
        .update_scan_mode = &ads1298_update_scan_mode,
        .debugfs_reg_access = &ads1298_reg_access,
};

static void ads1298_rdata_release_busy_or_restart(struct ads1298_private *priv)
{
        guard(spinlock_irqsave)(&priv->irq_busy_lock);

        if (priv->rdata_xfer_busy > 1) {
                /*
                 * DRDY interrupt occurred before SPI completion. Start a new
                 * SPI transaction now to retrieve the data that wasn't latched
                 * into the ADS1298 chip's transfer buffer yet.
                 */
                spi_async(priv->spi, &priv->rdata_msg);
                /*
                 * If more than one DRDY took place, there was an overrun. Since
                 * the sample is already lost, reset the counter to 1 so that
                 * we will wait for a DRDY interrupt after this SPI transaction.
                 */
                priv->rdata_xfer_busy = 1;
        } else {
                /* No pending data, wait for DRDY */
                priv->rdata_xfer_busy = 0;
        }
}

/* Called from SPI completion interrupt handler */
static void ads1298_rdata_complete(void *context)
{
        struct iio_dev *indio_dev = context;
        struct ads1298_private *priv = iio_priv(indio_dev);
        int scan_index;
        u32 *bounce = priv->bounce_buffer;

        if (!iio_buffer_enabled(indio_dev)) {
                /*
                 * for a single transfer mode we're kept in direct_mode until
                 * completion, avoiding a race with buffered IO.
                 */
                ads1298_rdata_unmark_busy(priv);
                complete(&priv->completion);
                return;
        }

        /* Demux the channel data into our bounce buffer */
        iio_for_each_active_channel(indio_dev, scan_index) {
                const struct iio_chan_spec *scan_chan =
                                        &indio_dev->channels[scan_index];
                const u8 *data = priv->rx_buffer + scan_chan->address;

                *bounce++ = get_unaligned_be24(data);
        }

        /* rx_buffer can be overwritten from this point on */
        ads1298_rdata_release_busy_or_restart(priv);

        iio_push_to_buffers(indio_dev, priv->bounce_buffer);
}

static irqreturn_t ads1298_interrupt(int irq, void *dev_id)
{
        struct iio_dev *indio_dev = dev_id;
        struct ads1298_private *priv = iio_priv(indio_dev);
        unsigned int wasbusy;

        guard(spinlock_irqsave)(&priv->irq_busy_lock);

        wasbusy = priv->rdata_xfer_busy++;
        /* When no SPI transfer in transit, start one now */
        if (!wasbusy)
                spi_async(priv->spi, &priv->rdata_msg);

        return IRQ_HANDLED;
};

static int ads1298_buffer_postenable(struct iio_dev *indio_dev)
{
        struct ads1298_private *priv = iio_priv(indio_dev);
        int ret;

        /* Disable single-shot mode */
        ret = regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG4,
                                 ADS1298_MASK_CONFIG4_SINGLE_SHOT, 0);
        if (ret)
                return ret;

        return ads1298_write_cmd(priv, ADS1298_CMD_START);
}

static int ads1298_buffer_predisable(struct iio_dev *indio_dev)
{
        struct ads1298_private *priv = iio_priv(indio_dev);

        return ads1298_write_cmd(priv, ADS1298_CMD_STOP);
}

static const struct iio_buffer_setup_ops ads1298_setup_ops = {
        .postenable = &ads1298_buffer_postenable,
        .predisable = &ads1298_buffer_predisable,
};

static void ads1298_reg_disable(void *reg)
{
        regulator_disable(reg);
}

static const struct regmap_range ads1298_regmap_volatile_range[] = {
        regmap_reg_range(ADS1298_REG_LOFF_STATP, ADS1298_REG_LOFF_STATN),
};

static const struct regmap_access_table ads1298_regmap_volatile = {
        .yes_ranges = ads1298_regmap_volatile_range,
        .n_yes_ranges = ARRAY_SIZE(ads1298_regmap_volatile_range),
};

static const struct regmap_config ads1298_regmap_config = {
        .reg_bits = 8,
        .val_bits = 8,
        .reg_read = ads1298_reg_read,
        .reg_write = ads1298_reg_write,
        .max_register = ADS1298_REG_WCT2,
        .volatile_table = &ads1298_regmap_volatile,
        .cache_type = REGCACHE_MAPLE,
};

static int ads1298_init(struct iio_dev *indio_dev)
{
        struct ads1298_private *priv = iio_priv(indio_dev);
        struct device *dev = &priv->spi->dev;
        const char *suffix;
        unsigned int val;
        int ret;

        /* Device initializes into RDATAC mode, which we don't want */
        ret = ads1298_write_cmd(priv, ADS1298_CMD_SDATAC);
        if (ret)
                return ret;

        ret = regmap_read(priv->regmap, ADS1298_REG_ID, &val);
        if (ret)
                return ret;

        /* Fill in name and channel count based on what the chip told us */
        indio_dev->num_channels = 4 + 2 * (val & ADS1298_MASK_ID_CHANNELS);
        switch (val & ADS1298_MASK_ID_FAMILY) {
        case ADS1298_ID_FAMILY_ADS129X:
                suffix = "";
                break;
        case ADS1298_ID_FAMILY_ADS129XR:
                suffix = "r";
                break;
        default:
                return dev_err_probe(dev, -ENODEV, "Unknown ID: 0x%x\n", val);
        }
        indio_dev->name = devm_kasprintf(dev, GFP_KERNEL, "ads129%u%s",
                                         indio_dev->num_channels, suffix);

        /* Enable internal test signal, double amplitude, double frequency */
        ret = regmap_write(priv->regmap, ADS1298_REG_CONFIG2,
                           ADS1298_MASK_CONFIG2_RESERVED |
                           ADS1298_MASK_CONFIG2_INT_TEST |
                           ADS1298_MASK_CONFIG2_TEST_AMP |
                           ADS1298_MASK_CONFIG2_TEST_FREQ_FAST);
        if (ret)
                return ret;

        val = ADS1298_MASK_CONFIG3_RESERVED; /* Must write 1 always */
        if (!priv->reg_vref) {
                /* Enable internal reference */
                val |= ADS1298_MASK_CONFIG3_PWR_REFBUF;
                /* Use 4V VREF when power supply is at least 4.4V */
                if (regulator_get_voltage(priv->reg_avdd) >= 4400000)
                        val |= ADS1298_MASK_CONFIG3_VREF_4V;
        }
        return regmap_write(priv->regmap, ADS1298_REG_CONFIG3, val);
}

static int ads1298_probe(struct spi_device *spi)
{
        struct ads1298_private *priv;
        struct iio_dev *indio_dev;
        struct device *dev = &spi->dev;
        struct gpio_desc *reset_gpio;
        int ret;

        indio_dev = devm_iio_device_alloc(dev, sizeof(*priv));
        if (!indio_dev)
                return -ENOMEM;

        priv = iio_priv(indio_dev);

        /* Reset to be asserted before enabling clock and power */
        reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
        if (IS_ERR(reset_gpio))
                return dev_err_probe(dev, PTR_ERR(reset_gpio),
                                     "Cannot get reset GPIO\n");

        /* VREF can be supplied externally, otherwise use internal reference */
        priv->reg_vref = devm_regulator_get_optional(dev, "vref");
        if (IS_ERR(priv->reg_vref)) {
                if (PTR_ERR(priv->reg_vref) != -ENODEV)
                        return dev_err_probe(dev, PTR_ERR(priv->reg_vref),
                                             "Failed to get vref regulator\n");

                priv->reg_vref = NULL;
        } else {
                ret = regulator_enable(priv->reg_vref);
                if (ret)
                        return ret;

                ret = devm_add_action_or_reset(dev, ads1298_reg_disable, priv->reg_vref);
                if (ret)
                        return ret;
        }

        priv->clk = devm_clk_get_optional_enabled(dev, "clk");
        if (IS_ERR(priv->clk))
                return dev_err_probe(dev, PTR_ERR(priv->clk), "Failed to get clk\n");

        priv->reg_avdd = devm_regulator_get(dev, "avdd");
        if (IS_ERR(priv->reg_avdd))
                return dev_err_probe(dev, PTR_ERR(priv->reg_avdd),
                                     "Failed to get avdd regulator\n");

        ret = regulator_enable(priv->reg_avdd);
        if (ret)
                return dev_err_probe(dev, ret, "Failed to enable avdd regulator\n");

        ret = devm_add_action_or_reset(dev, ads1298_reg_disable, priv->reg_avdd);
        if (ret)
                return ret;

        priv->spi = spi;
        init_completion(&priv->completion);
        spin_lock_init(&priv->irq_busy_lock);
        priv->regmap = devm_regmap_init(dev, NULL, priv, &ads1298_regmap_config);
        if (IS_ERR(priv->regmap))
                return PTR_ERR(priv->regmap);

        indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_SOFTWARE;
        indio_dev->channels = ads1298_channels;
        indio_dev->info = &ads1298_info;

        if (reset_gpio) {
                /*
                 * Deassert reset now that clock and power are active.
                 * Minimum reset pulsewidth is 2 clock cycles.
                 */
                fsleep(ADS1298_CLOCKS_TO_USECS(2));
                gpiod_set_value_cansleep(reset_gpio, 0);
        } else {
                ret = ads1298_write_cmd(priv, ADS1298_CMD_RESET);
                if (ret)
                        return dev_err_probe(dev, ret, "RESET failed\n");
        }
        /* Wait 18 clock cycles for reset command to complete */
        fsleep(ADS1298_CLOCKS_TO_USECS(18));

        ret = ads1298_init(indio_dev);
        if (ret)
                return dev_err_probe(dev, ret, "Init failed\n");

        priv->tx_buffer[0] = ADS1298_CMD_RDATA;
        priv->rdata_xfer.tx_buf = priv->tx_buffer;
        priv->rdata_xfer.rx_buf = priv->rx_buffer;
        priv->rdata_xfer.len = ADS1298_SPI_RDATA_BUFFER_SIZE(indio_dev->num_channels);
        /* Must keep CS low for 4 clocks */
        priv->rdata_xfer.delay.value = 2;
        priv->rdata_xfer.delay.unit = SPI_DELAY_UNIT_USECS;
        spi_message_init_with_transfers(&priv->rdata_msg, &priv->rdata_xfer, 1);
        priv->rdata_msg.complete = &ads1298_rdata_complete;
        priv->rdata_msg.context = indio_dev;

        ret = devm_request_irq(dev, spi->irq, &ads1298_interrupt,
                               IRQF_TRIGGER_FALLING, indio_dev->name,
                               indio_dev);
        if (ret)
                return ret;

        ret = devm_iio_kfifo_buffer_setup(dev, indio_dev, &ads1298_setup_ops);
        if (ret)
                return ret;

        return devm_iio_device_register(dev, indio_dev);
}

static const struct spi_device_id ads1298_id[] = {
        { "ads1298" },
        { }
};
MODULE_DEVICE_TABLE(spi, ads1298_id);

static const struct of_device_id ads1298_of_table[] = {
        { .compatible = "ti,ads1298" },
        { }
};
MODULE_DEVICE_TABLE(of, ads1298_of_table);

static struct spi_driver ads1298_driver = {
        .driver = {
                .name   = "ads1298",
                .of_match_table = ads1298_of_table,
        },
        .probe          = ads1298_probe,
        .id_table       = ads1298_id,
};
module_spi_driver(ads1298_driver);

MODULE_AUTHOR("Mike Looijmans <mike.looijmans@topic.nl>");
MODULE_DESCRIPTION("TI ADS1298 ADC");
MODULE_LICENSE("GPL");