[RFC PATCH 1/5] iio: adc: ti-ads1262.c: add initial driver for TI ADS1262 ADC

[Sayyad Abid <sayyad.abid16@gmail.com>]

Add the core driver file `ti-ads1262.c` for the TI ADS1262 ADC.
This initial version implements basic IIO functionality for device
probe via SPI and reading raw voltage samples from input channels.

Signed-off-by: Sayyad Abid <sayyad.abid16@gmail.com>
---
 drivers/iio/adc/ti-ads1262.c | 438 +++++++++++++++++++++++++++++++++++
 1 file changed, 438 insertions(+)
 create mode 100644 drivers/iio/adc/ti-ads1262.c

diff --git a/drivers/iio/adc/ti-ads1262.c b/drivers/iio/adc/ti-ads1262.c
new file mode 100644
index 000000000000..ef34c528ffeb
--- /dev/null
+++ b/drivers/iio/adc/ti-ads1262.c
@@ -0,0 +1,438 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IIO driver for Texas Instruments ADS1662 32-bit ADC
+ *
+ * Datasheet: https://www.ti.com/product/ADS1262
+ */
+
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/delay.h>
+#include <linux/spi/spi.h>
+#include <linux/unaligned.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/triggered_buffer.h>
+
+/* Commands */
+#define ADS1262_CMD_RESET		0x06
+#define ADS1262_CMD_START1		0x08
+#define ADS1262_CMD_STOP1		0x0A
+#define ADS1262_CMD_RDATA1		0x12
+#define ADS1262_CMD_RREG		0x20
+#define ADS1262_CMD_WREG		0x40
+
+/* Registers */
+#define ADS1262_REG_ID			0x00
+#define ADS1262_REG_POWER		0x01
+#define ADS1262_REG_INTERFACE		0x02
+#define ADS1262_REG_MODE0		0x03
+#define ADS1262_REG_MODE1		0x04
+#define ADS1262_REG_MODE2		0x05
+#define ADS1262_REG_INPMUX		0x06
+
+/* Configurations */
+#define ADS1262_INTREF_ENABLE		0x01
+#define ADS1262_MODE0_ONE_SHOT		0x40
+#define ADS1262_MODE2_PGA_EN		0x00
+#define ADS1262_MODE2_PGA_BYPASS	BIT(7)
+
+/* Masks */
+#define ADS1262_MASK_MODE2_DR		GENMASK(4, 0)
+
+/* ADS1262_SPECS */
+#define ADS1262_MAX_CHANNELS		11
+#define ADS1262_BITS_PER_SAMPLE		32
+#define ADS1262_CLK_RATE_HZ		7372800
+#define ADS1262_CLOCKS_TO_USECS(x)	\
+	(DIV_ROUND_UP((x) * MICROHZ_PER_HZ, ADS1262_CLK_RATE_HZ))
+#define ADS1262_VOLTAGE_INT_REF_uV	2500000
+#define ADS1262_TEMP_SENSITIVITY_uV_per_C 420
+
+#define ADS1262_SETTLE_TIME_USECS	10000
+
+/* The Read/Write commands require 4 tCLK to encode and decode, for speeds
+ * 2x the clock rate, these commands would require extra time between the
+ * command byte and the data. A simple way to tacke this issue is by
+ * limiting the SPI bus transfer speed while accessing registers.
+ */
+#define ADS1262_SPI_BUS_SPEED_SLOW	ADS1262_CLK_RATE_HZ
+
+/* For reading and writing we need a buffer of size 3bytes*/
+#define ADS1262_SPI_CMD_BUFFER_SIZE	3
+
+/* Read data buffer size for
+ * 1 status byte - 4 byte data (32 bit) - 1 byte checksum / CRC
+ */
+#define ADS1262_SPI_RDATA_BUFFER_SIZE	6
+
+#define MILLI				1000
+
+/**
+ * struct ads1262_private - ADS1262 ADC private data structure
+ * @spi: SPI device structure
+ * @reset_gpio: GPIO descriptor for reset pin
+ * @prev_channel: Previously selected channel for MUX configuration
+ * @cmd_buffer: Buffer for SPI command transfers
+ * @rx_buffer: Buffer for SPI data reception
+ */
+struct ads1262_private {
+	struct spi_device *spi;
+	struct gpio_desc *reset_gpio;
+	u8 prev_channel;
+	u8 cmd_buffer[ADS1262_SPI_CMD_BUFFER_SIZE];
+	u8 rx_buffer[ADS1262_SPI_RDATA_BUFFER_SIZE] __aligned(IIO_DMA_MINALIGN);
+};
+
+#define ADS1262_CHAN(index)						\
+{									\
+	.type = IIO_VOLTAGE,						\
+	.indexed = 1,							\
+	.channel = index,						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),			\
+	.scan_index = index,						\
+	.scan_type = {							\
+		.sign = 's',						\
+		.realbits = ADS1262_BITS_PER_SAMPLE,			\
+		.storagebits = 32,					\
+		.endianness = IIO_CPU					\
+	},								\
+}
+
+#define ADS1262_DIFF_CHAN(index, pos_channel, neg_channel)		\
+{									\
+	.type = IIO_VOLTAGE,						\
+	.indexed = 1,							\
+	.channel = pos_channel,						\
+	.channel2 = neg_channel,					\
+	.differential = 1,						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),			\
+	.scan_index = index,						\
+	.scan_type = {							\
+		.sign = 's',						\
+		.realbits = ADS1262_BITS_PER_SAMPLE,			\
+		.storagebits = 32,					\
+		.endianness = IIO_CPU					\
+	},								\
+}
+
+#define ADS1262_TEMP_CHAN(index)					\
+{									\
+	.type = IIO_TEMP,						\
+	.indexed = 1,							\
+	.channel = index,						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
+			     BIT(IIO_CHAN_INFO_SCALE) |			\
+			     BIT(IIO_CHAN_INFO_SAMP_FREQ),		\
+	.scan_index = index,						\
+	.scan_type = {							\
+		.sign = 's',						\
+		.realbits = ADS1262_BITS_PER_SAMPLE,			\
+		.storagebits = 32,					\
+		.endianness = IIO_BE,					\
+	},								\
+}
+
+static const struct iio_chan_spec ads1262_channels[] = {
+	/* Single ended channels*/
+	ADS1262_CHAN(0),
+	ADS1262_CHAN(1),
+	ADS1262_CHAN(2),
+	ADS1262_CHAN(3),
+	ADS1262_CHAN(4),
+	ADS1262_CHAN(5),
+	ADS1262_CHAN(6),
+	ADS1262_CHAN(7),
+	ADS1262_CHAN(8),
+	ADS1262_CHAN(9),
+	/* The channel at index 10 is AINCOM, which is the common ground
+	 * of the ADC. It is not a valid channel for the user.
+	 */
+
+	/* Temperature and Monitor channels */
+	ADS1262_TEMP_CHAN(11),	/* TEMP SENSOR */
+	ADS1262_CHAN(12),	/* AVDD MON */
+	ADS1262_CHAN(13),	/* DVDD MON */
+	ADS1262_CHAN(14),	/* TDAC TEST */
+	/* Differential channels */
+	ADS1262_DIFF_CHAN(15, 0, 1),	/* AIN0 - AIN1 */
+	ADS1262_DIFF_CHAN(16, 2, 3),	/* AIN2 - AIN3 */
+	ADS1262_DIFF_CHAN(17, 4, 5),	/* AIN4 - AIN5 */
+	ADS1262_DIFF_CHAN(18, 6, 7),	/* AIN6 - AIN7 */
+	ADS1262_DIFF_CHAN(19, 8, 9),	/* AIN8 - AIN9 */
+};
+
+static int ads1262_write_cmd(struct ads1262_private *priv, u8 command)
+{
+	struct spi_transfer xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->rx_buffer,
+		.len = ADS1262_SPI_RDATA_BUFFER_SIZE,
+		.speed_hz = ADS1262_CLK_RATE_HZ,
+	};
+
+	priv->cmd_buffer[0] = command;
+
+	return spi_sync_transfer(priv->spi, &xfer, 1);
+}
+
+static int ads1262_reg_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct ads1262_private *priv = context;
+
+	priv->cmd_buffer[0] = ADS1262_CMD_WREG | reg;
+	priv->cmd_buffer[1] = 0;
+	priv->cmd_buffer[2] = val;
+
+	return spi_write(priv->spi, &priv->cmd_buffer[0], 3);
+}
+
+static int ads1262_reg_read(void *context, unsigned int reg)
+{
+	struct ads1262_private *priv = context;
+	struct spi_transfer reg_read_xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->cmd_buffer,
+		.len = 3,
+		.speed_hz = ADS1262_CLK_RATE_HZ,
+	};
+	int ret;
+
+	priv->cmd_buffer[0] = ADS1262_CMD_RREG | reg;
+	priv->cmd_buffer[1] = 0;
+	priv->cmd_buffer[2] = 0;
+
+	ret = spi_sync_transfer(priv->spi, &reg_read_xfer, 1);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int ads1262_reset(struct iio_dev *indio_dev)
+{
+	struct ads1262_private *priv = iio_priv(indio_dev);
+
+	if (priv->reset_gpio) {
+		gpiod_set_value(priv->reset_gpio, 0);
+		usleep_range(200, 300);
+		gpiod_set_value(priv->reset_gpio, 1);
+	} else {
+		return ads1262_write_cmd(priv, ADS1262_CMD_RESET);
+	}
+	return 0;
+}
+
+static int ads1262_init(struct iio_dev *indio_dev)
+{
+	struct ads1262_private *priv = iio_priv(indio_dev);
+	int ret = 0;
+
+	ret = ads1262_reset(indio_dev);
+	if (ret)
+		return ret;
+
+	/* 10 milliseconds settling time for the ADC to stabilize */
+	fsleep(ADS1262_SETTLE_TIME_USECS);
+
+	/* Clearing the RESET bit in the power register to detect ADC reset */
+	ret = ads1262_reg_write(priv, ADS1262_REG_POWER, ADS1262_INTREF_ENABLE);
+	if (ret)
+		return ret;
+
+	/* Setting the ADC to one-shot conversion mode */
+	ret = ads1262_reg_write(priv, ADS1262_REG_MODE0, ADS1262_MODE0_ONE_SHOT);
+	if (ret)
+		return ret;
+
+	ret = ads1262_reg_read(priv, ADS1262_REG_INPMUX);
+	if (ret)
+		return ret;
+
+	priv->prev_channel = priv->cmd_buffer[2];
+
+	return ret;
+}
+
+static int ads1262_get_samp_freq(struct ads1262_private *priv, int *val)
+{
+	unsigned long samp_freq;
+	int ret;
+
+	ret = ads1262_reg_read(priv, ADS1262_REG_MODE2);
+	if (ret)
+		return ret;
+
+	samp_freq = priv->cmd_buffer[2];
+
+	*val = (samp_freq & ADS1262_MASK_MODE2_DR);
+
+	return IIO_VAL_INT;
+}
+
+/**
+ * ads1262_read - Read a single sample from the ADC
+ * @priv: Pointer to the ADS1262 private data structure
+ * @chan: Pointer to the IIO channel specification
+ * @val: Pointer to store the read value
+ *
+ * Reads a single sample from the specified ADC channel. For differential
+ * channels, it sets up the MUX with both channels. For single-ended channels,
+ * it uses the channel number and AINCOM (0x0A).
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int ads1262_read(struct ads1262_private *priv,
+			struct iio_chan_spec const *chan, int *val)
+{
+	u8 mux_value;
+	int ret;
+
+	if (chan->differential) {
+		mux_value = (chan->channel << 4) | chan->channel2;
+	} else {
+		/* For single-ended channels, use the channel number on one end
+		 * and AINCOM (0x0A) on the other end
+		 */
+		mux_value = (chan->channel << 4) | 0x0A;
+	}
+
+	if (mux_value != priv->prev_channel) {
+		ret = ads1262_write_cmd(priv, ADS1262_CMD_STOP1);
+		if (ret)
+			return ret;
+
+		ret = ads1262_reg_write(priv, ADS1262_REG_INPMUX, mux_value);
+		if (ret)
+			return ret;
+
+		priv->prev_channel = mux_value;
+	}
+
+	ret = ads1262_write_cmd(priv, ADS1262_CMD_START1);
+	if (ret)
+		return ret;
+
+	usleep_range(1000, 2000);
+
+	*val = sign_extend64(get_unaligned_be32(priv->rx_buffer + 1),
+			     ADS1262_BITS_PER_SAMPLE - 1);
+
+	return 0;
+}
+
+static int ads1262_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ads1262_private *spi = iio_priv(indio_dev);
+	s64 temp;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ads1262_read(spi, chan, val);
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = ADS1262_VOLTAGE_INT_REF_uV;
+			*val2 = chan->scan_type.realbits;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		case IIO_TEMP:
+			temp = (s64)ADS1262_VOLTAGE_INT_REF_uV * MILLI;
+			temp /= ADS1262_TEMP_SENSITIVITY_uV_per_C;
+			*val = temp;
+			*val2 = chan->scan_type.realbits;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		return ads1262_get_samp_freq(spi, val);
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ads1262_info = {
+	.read_raw = ads1262_read_raw,
+};
+
+static void ads1262_stop(void *ptr)
+{
+	struct ads1262_private *adc = ptr;
+
+	ads1262_write_cmd(adc, ADS1262_CMD_STOP1);
+}
+
+static int ads1262_probe(struct spi_device *spi)
+{
+	struct ads1262_private *adc;
+	struct iio_dev *indio_dev;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*adc));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	adc = iio_priv(indio_dev);
+	adc->spi = spi;
+
+	spi->mode = SPI_MODE_1;
+	spi->max_speed_hz = ADS1262_SPI_BUS_SPEED_SLOW;
+	spi_set_drvdata(spi, indio_dev);
+
+	indio_dev->dev.parent = &spi->dev;
+	indio_dev->name = spi_get_device_id(spi)->name;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = ads1262_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ads1262_channels);
+	indio_dev->info = &ads1262_info;
+
+	ret = ads1262_reg_read(adc, ADS1262_REG_ID);
+	if (ret)
+		return ret;
+
+	if (adc->rx_buffer[2] != ADS1262_REG_ID)
+		dev_err_probe(&spi->dev, -EINVAL, "Wrong device ID 0x%x\n",
+			      adc->rx_buffer[2]);
+
+	ret = devm_add_action_or_reset(&spi->dev, ads1262_stop, adc);
+	if (ret)
+		return ret;
+
+	ret = ads1262_init(indio_dev);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static struct spi_device_id ads1262_id_table[] = {
+	{ "ads1262" },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, ads1262_id_table);
+
+static const struct of_device_id ads1262_of_match[] = {
+	{ .compatible = "ti,ads1262" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, ads1262_of_match);
+
+static struct spi_driver ads1262_driver = {
+	.driver = {
+		.name = "ads1262",
+		.of_match_table = ads1262_of_match,
+	},
+	.probe = ads1262_probe,
+	.id_table = ads1262_id_table,
+};
+module_spi_driver(ads1262_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sayyad Abid <sayyad.abid16@gmail.com>");
+MODULE_DESCRIPTION("TI ADS1262 ADC");
-- 
2.39.5