[v2,2/2] iio: adc: ti-ads1298: Add driver

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 35f9867da12c..1d2d2eff15da 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1318,6 +1318,17 @@  config TI_ADS8688
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-ads8688.
 
+config TI_ADS1298
+	tristate "Texas Instruments ADS1298"
+	depends on SPI
+	select IIO_BUFFER
+	help
+	  If you say yes here you get support for Texas Instruments ADS1298
+	  medical ADC chips
+
+	  This driver can also be built as a module. If so, the module will be
+	  called ti-ads1298.
+
 config TI_ADS124S08
 	tristate "Texas Instruments ADS124S08"
 	depends on SPI
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index bee11d442af4..ff0e3633eded 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -117,6 +117,7 @@  obj-$(CONFIG_TI_ADS7924) += ti-ads7924.o
 obj-$(CONFIG_TI_ADS7950) += ti-ads7950.o
 obj-$(CONFIG_TI_ADS8344) += ti-ads8344.o
 obj-$(CONFIG_TI_ADS8688) += ti-ads8688.o
+obj-$(CONFIG_TI_ADS1298) += ti-ads1298.o
 obj-$(CONFIG_TI_ADS124S08) += ti-ads124s08.o
 obj-$(CONFIG_TI_ADS131E08) += ti-ads131e08.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
diff --git a/drivers/iio/adc/ti-ads1298.c b/drivers/iio/adc/ti-ads1298.c
new file mode 100644
index 000000000000..539598b9f3fa
--- /dev/null
+++ b/drivers/iio/adc/ti-ads1298.c
@@ -0,0 +1,769 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* TI ADS1298 chip family driver
+ * Copyright (C) 2023 - 2024 Topic Embedded Products
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.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/sysfs.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/kfifo_buf.h>
+#include <linux/iio/sysfs.h>
+
+#include <asm/unaligned.h>
+
+#define ADS1298_WAKEUP  0x02
+#define ADS1298_STANDBY 0x04
+#define ADS1298_RESET   0x06
+#define ADS1298_START   0x08
+#define ADS1298_STOP    0x0A
+#define ADS1298_RDATAC  0x10
+#define ADS1298_SDATAC  0x11
+#define ADS1298_RDATA   0x12
+
+/* 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			0x07
+#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_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 8 24-bit samples, plus the command byte */
+#define ADS1298_SPI_RDATA_BUFFER_SIZE	((ADS1298_MAX_CHANNELS + 1) * 3 + 1)
+
+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 */
+	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];
+	/* Contains the RDATA command and zeroes to clock out */
+	u8 tx_buffer[ADS1298_SPI_RDATA_BUFFER_SIZE];
+};
+
+/* 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 = 24,				\
+		.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 cmd_xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->cmd_buffer,
+		.len = sizeof(command),
+		.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, &cmd_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;
+	int ret;
+	unsigned int cfg;
+
+	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;
+
+	factor = (rate >> ADS1298_SHIFT_DR_HR) / val;
+	if (factor >= 128) {
+		cfg = ADS1298_LOWEST_DR;
+	} else if (factor <= 1) {
+		cfg = ADS1298_MASK_CONFIG1_HR; /* Fastest possible */
+	} else {
+		cfg = fls(factor) - 1;
+		cfg |= ADS1298_MASK_CONFIG1_HR; /* Use HR mode */
+	}
+
+	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 / 1000; /* Convert to millivolts */
+	} else {
+		ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG3, &regval);
+		if (ret)
+			return ret;
+
+		/* Refererence 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 = 23; /* Signed 24-bit, max amplitude is 2^23 */
+
+	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),
+				     23);
+		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] = 0x0;
+	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] = 0x0;
+	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)
+{
+	unsigned long flags;
+
+	/* Notify we're no longer waiting for the SPI transfer to complete */
+	spin_lock_irqsave(&priv->irq_busy_lock, flags);
+	priv->rdata_xfer_busy = 0;
+	spin_unlock_irqrestore(&priv->irq_busy_lock, flags);
+}
+
+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);
+
+	/* Power down channels that aren't in use */
+	for (i = 0; i < ADS1298_MAX_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)
+{
+	unsigned long flags;
+	int wasbusy;
+
+	spin_lock_irqsave(&priv->irq_busy_lock, flags);
+
+	wasbusy = --priv->rdata_xfer_busy;
+	if (wasbusy) {
+		/*
+		 * 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.
+		 */
+		if (wasbusy > 1)
+			priv->rdata_xfer_busy = 1;
+	}
+
+	spin_unlock_irqrestore(&priv->irq_busy_lock, flags);
+}
+
+/* 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)) {
+		/* Happens when running in single transfer mode */
+		ads1298_rdata_unmark_busy(priv);
+		complete(&priv->completion);
+		return;
+	}
+
+	/* Demux the channel data into our bounce buffer */
+	for_each_set_bit(scan_index, indio_dev->active_scan_mask,
+			 indio_dev->masklength) {
+		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 long flags;
+	int wasbusy;
+
+	spin_lock_irqsave(&priv->irq_busy_lock, flags);
+
+	wasbusy = priv->rdata_xfer_busy++;
+	/* When no SPI transfer in transit, start one now */
+	if (!wasbusy)
+		spi_async(priv->spi, &priv->rdata_msg);
+
+	spin_unlock_irqrestore(&priv->irq_busy_lock, flags);
+
+	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_RBTREE,
+};
+
+static const char *ads1298_family_name(unsigned int id)
+{
+	switch (id & ADS1298_MASK_ID_FAMILY) {
+	case ADS1298_ID_FAMILY_ADS129X:
+		return "ADS129x";
+	case ADS1298_ID_FAMILY_ADS129XR:
+		return "ADS129xR";
+	default:
+		return "(unknown)";
+	}
+}
+
+static int ads1298_init(struct ads1298_private *priv)
+{
+	struct device *dev = &priv->spi->dev;
+	int ret;
+	unsigned int val;
+
+	/* 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;
+
+	dev_info(dev, "Found %s, %u channels\n", ads1298_family_name(val),
+		 4 + 2 * (val & ADS1298_MASK_ID_CHANNELS));
+
+	/* 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_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return dev_err_probe(dev, ret, "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)
+			priv->reg_vref = NULL;
+		else
+			return dev_err_probe(dev, PTR_ERR(priv->reg_avdd),
+					     "Failed to get vref regulator\n");
+	} 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_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);
+
+	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;
+	/* 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;
+
+	indio_dev->name = spi_get_device_id(spi)->name;
+	indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_SOFTWARE;
+	indio_dev->channels = ads1298_channels;
+	indio_dev->num_channels = ADS1298_MAX_CHANNELS;
+	indio_dev->info = &ads1298_info;
+
+	if (reset_gpio) {
+		udelay(ADS1298_CLOCKS_TO_USECS(2));
+		gpiod_set_value(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 */
+	udelay(ADS1298_CLOCKS_TO_USECS(18));
+
+	ret = ads1298_init(priv);
+	if (ret)
+		return dev_err_probe(dev, ret, "Init failed\n");
+
+	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");