iio: adc: add ADC driver for the TI LMP92064 controller

The TI LMP92064 is a dual 12 Bit ADC connected via SPI.
The two channels are intended for simultaneous measurements of the voltage
across- and current through a load to allow accurate instantaneous power
measurements.
The driver does not yet take advantage of this feature, as buffering is not
yet implemented.

Signed-off-by: Leonard Göhrs <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 F:	sound/soc/codecs/isabelle*
 F:	sound/soc/codecs/lm49453*
 
+TI LMP92064 ADC DRIVER
+M:	Leonard Göhrs <[e-mail]>
+R:	[e-mail]
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/adc/ti,lmp92064.yaml
+F:	drivers/iio/adc/ti-lmp92064.c
+
 TI PCM3060 ASoC CODEC DRIVER
 M:	Kirill Marinushkin <[e-mail]>
 L:	[e-mail] (moderated for non-subscribers)

drivers/iio/adc/Kconfig

···
 	  To compile this driver as a module, choose M here: the module will be
 	  called ti_am335x_adc.
 
+config TI_LMP92064
+	tristate "Texas Instruments LMP92064 ADC driver"
+	depends on SPI
+	help
+	  Say yes here to build support for the LMP92064 Precision Current and Voltage
+	  sensor.
+
+	  This driver can also be built as a module. If so, the module will be called
+	  ti-lmp92064.
+
 config TI_TLC4541
 	tristate "Texas Instruments TLC4541 ADC driver"
 	depends on SPI

drivers/iio/adc/Makefile

···
 obj-$(CONFIG_TI_ADS124S08) += ti-ads124s08.o
 obj-$(CONFIG_TI_ADS131E08) += ti-ads131e08.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
+obj-$(CONFIG_TI_LMP92064) += ti-lmp92064.o
 obj-$(CONFIG_TI_TLC4541) += ti-tlc4541.o
 obj-$(CONFIG_TI_TSC2046) += ti-tsc2046.o
 obj-$(CONFIG_TWL4030_MADC) += twl4030-madc.o

drivers/iio/adc/ti-lmp92064.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Texas Instruments LMP92064 SPI ADC driver
+ *
+ * Copyright (c) 2022 Leonard Göhrs <[e-mail]>, Pengutronix
+ *
+ * Based on linux/drivers/iio/adc/ti-tsc2046.c
+ * Copyright (c) 2021 Oleksij Rempel <[e-mail]>, Pengutronix
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/driver.h>
+
+#define TI_LMP92064_REG_CONFIG_A 0x0000
+#define TI_LMP92064_REG_CONFIG_B 0x0001
+#define TI_LMP92064_REG_CHIP_REV 0x0006
+
+#define TI_LMP92064_REG_MFR_ID1 0x000C
+#define TI_LMP92064_REG_MFR_ID2 0x000D
+
+#define TI_LMP92064_REG_REG_UPDATE 0x000F
+#define TI_LMP92064_REG_CONFIG_REG 0x0100
+#define TI_LMP92064_REG_STATUS 0x0103
+
+#define TI_LMP92064_REG_DATA_VOUT_LSB 0x0200
+#define TI_LMP92064_REG_DATA_VOUT_MSB 0x0201
+#define TI_LMP92064_REG_DATA_COUT_LSB 0x0202
+#define TI_LMP92064_REG_DATA_COUT_MSB 0x0203
+
+#define TI_LMP92064_VAL_CONFIG_A 0x99
+#define TI_LMP92064_VAL_CONFIG_B 0x00
+#define TI_LMP92064_VAL_STATUS_OK 0x01
+
+/*
+ * Channel number definitions for the two channels of the device
+ * - IN Current (INC)
+ * - IN Voltage (INV)
+ */
+#define TI_LMP92064_CHAN_INC 0
+#define TI_LMP92064_CHAN_INV 1
+
+static const struct regmap_range lmp92064_readable_reg_ranges[] = {
+	regmap_reg_range(TI_LMP92064_REG_CONFIG_A, TI_LMP92064_REG_CHIP_REV),
+	regmap_reg_range(TI_LMP92064_REG_MFR_ID1, TI_LMP92064_REG_MFR_ID2),
+	regmap_reg_range(TI_LMP92064_REG_REG_UPDATE, TI_LMP92064_REG_REG_UPDATE),
+	regmap_reg_range(TI_LMP92064_REG_CONFIG_REG, TI_LMP92064_REG_CONFIG_REG),
+	regmap_reg_range(TI_LMP92064_REG_STATUS, TI_LMP92064_REG_STATUS),
+	regmap_reg_range(TI_LMP92064_REG_DATA_VOUT_LSB, TI_LMP92064_REG_DATA_COUT_MSB),
+};
+
+static const struct regmap_access_table lmp92064_readable_regs = {
+	.yes_ranges = lmp92064_readable_reg_ranges,
+	.n_yes_ranges = ARRAY_SIZE(lmp92064_readable_reg_ranges),
+};
+
+static const struct regmap_range lmp92064_writable_reg_ranges[] = {
+	regmap_reg_range(TI_LMP92064_REG_CONFIG_A, TI_LMP92064_REG_CONFIG_B),
+	regmap_reg_range(TI_LMP92064_REG_REG_UPDATE, TI_LMP92064_REG_REG_UPDATE),
+	regmap_reg_range(TI_LMP92064_REG_CONFIG_REG, TI_LMP92064_REG_CONFIG_REG),
+};
+
+static const struct regmap_access_table lmp92064_writable_regs = {
+	.yes_ranges = lmp92064_writable_reg_ranges,
+	.n_yes_ranges = ARRAY_SIZE(lmp92064_writable_reg_ranges),
+};
+
+static const struct regmap_config lmp92064_spi_regmap_config = {
+	.reg_bits = 16,
+	.val_bits = 8,
+	.max_register = TI_LMP92064_REG_DATA_COUT_MSB,
+	.rd_table = &lmp92064_readable_regs,
+	.wr_table = &lmp92064_writable_regs,
+};
+
+struct lmp92064_adc_priv {
+	int shunt_resistor_uohm;
+	struct spi_device *spi;
+	struct regmap *regmap;
+};
+
+static const struct iio_chan_spec lmp92064_adc_channels[] = {
+	{
+		.type = IIO_CURRENT,
+		.address = TI_LMP92064_CHAN_INC,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.datasheet_name = "INC",
+	},
+	{
+		.type = IIO_VOLTAGE,
+		.address = TI_LMP92064_CHAN_INV,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.datasheet_name = "INV",
+	},
+};
+
+static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
+{
+	__be16 raw[2];
+	int ret;
+
+	/*
+	 * The ADC only latches in new samples if all DATA registers are read
+	 * in descending sequential order.
+	 * The ADC auto-decrements the register index with each clocked byte.
+	 * Read both channels in single SPI transfer by selecting the highest
+	 * register using the command below and clocking out all four data
+	 * bytes.
+	 */
+
+	ret = regmap_bulk_read(priv->regmap, TI_LMP92064_REG_DATA_COUT_MSB,
+			 &raw, sizeof(raw));
+
+	if (ret) {
+		dev_err(&priv->spi->dev, "regmap_bulk_read failed: %pe\n",
+			ERR_PTR(ret));
+		return ret;
+	}
+
+	res[0] = be16_to_cpu(raw[0]);
+	res[1] = be16_to_cpu(raw[1]);
+
+	return 0;
+}
+
+static int lmp92064_read_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int *val,
+			     int *val2, long mask)
+{
+	struct lmp92064_adc_priv *priv = iio_priv(indio_dev);
+	u16 raw[2];
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = lmp92064_read_meas(priv, raw);
+		if (ret < 0)
+			return ret;
+
+		*val = (chan->address == TI_LMP92064_CHAN_INC) ? raw[0] : raw[1];
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->address == TI_LMP92064_CHAN_INC) {
+			/*
+			 * processed (mA) = raw * current_lsb (mA)
+			 * current_lsb (mA) = shunt_voltage_lsb (nV) / shunt_resistor (uOhm)
+			 * shunt_voltage_lsb (nV) = 81920000 / 4096 = 20000
+			 */
+			*val = 20000;
+			*val2 = priv->shunt_resistor_uohm;
+		} else {
+			/*
+			 * processed (mV) = raw * voltage_lsb (mV)
+			 * voltage_lsb (mV) = 2048 / 4096
+			 */
+			*val = 2048;
+			*val2 = 4096;
+		}
+		return IIO_VAL_FRACTIONAL;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int lmp92064_reset(struct lmp92064_adc_priv *priv,
+			  struct gpio_desc *gpio_reset)
+{
+	unsigned int status;
+	int ret, i;
+
+	if (gpio_reset) {
+		/*
+		 * Perform a hard reset if gpio_reset is available.
+		 * The datasheet specifies a very low 3.5ns reset pulse duration and does not
+		 * specify how long to wait after a reset to access the device.
+		 * Use more conservative pulse lengths to allow analog RC filtering of the
+		 * reset line at the board level (as recommended in the datasheet).
+		 */
+		gpiod_set_value_cansleep(gpio_reset, 1);
+		usleep_range(1, 10);
+		gpiod_set_value_cansleep(gpio_reset, 0);
+		usleep_range(500, 750);
+	} else {
+		/*
+		 * Perform a soft-reset if not.
+		 * Also write default values to the config registers that are not
+		 * affected by soft reset.
+		 */
+		ret = regmap_write(priv->regmap, TI_LMP92064_REG_CONFIG_A,
+				   TI_LMP92064_VAL_CONFIG_A);
+		if (ret < 0)
+			return ret;
+
+		ret = regmap_write(priv->regmap, TI_LMP92064_REG_CONFIG_B,
+				   TI_LMP92064_VAL_CONFIG_B);
+		if (ret < 0)
+			return ret;
+	}
+
+	/*
+	 * Wait for the device to signal readiness to prevent reading bogus data
+	 * and make sure device is actually connected.
+	 * The datasheet does not specify how long this takes but usually it is
+	 * not more than 3-4 iterations of this loop.
+	 */
+	for (i = 0; i < 10; i++) {
+		ret = regmap_read(priv->regmap, TI_LMP92064_REG_STATUS, &status);
+		if (ret < 0)
+			return ret;
+
+		if (status == TI_LMP92064_VAL_STATUS_OK)
+			return 0;
+
+		usleep_range(1000, 2000);
+	}
+
+	/*
+	 * No (correct) response received.
+	 * Device is mostly likely not connected to the bus.
+	 */
+	return -ENXIO;
+}
+
+static const struct iio_info lmp92064_adc_info = {
+	.read_raw = lmp92064_read_raw,
+};
+
+static int lmp92064_adc_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct lmp92064_adc_priv *priv;
+	struct gpio_desc *gpio_reset;
+	struct iio_dev *indio_dev;
+	u32 shunt_resistor_uohm;
+	struct regmap *regmap;
+	int ret;
+
+	ret = spi_setup(spi);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Error in SPI setup\n");
+
+	regmap = devm_regmap_init_spi(spi, &lmp92064_spi_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "Failed to set up SPI regmap\n");
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*priv));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	priv = iio_priv(indio_dev);
+
+	priv->spi = spi;
+	priv->regmap = regmap;
+
+	ret = device_property_read_u32(dev, "shunt-resistor-micro-ohms",
+				       &shunt_resistor_uohm);
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "Failed to get shunt-resistor value\n");
+
+	/*
+	 * The shunt resistance is passed to userspace as the denominator of an iio
+	 * fraction. Make sure it is in range for that.
+	 */
+	if (shunt_resistor_uohm == 0 || shunt_resistor_uohm > INT_MAX) {
+		dev_err(dev, "Shunt resistance is out of range\n");
+		return -EINVAL;
+	}
+
+	priv->shunt_resistor_uohm = shunt_resistor_uohm;
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return ret;
+
+	ret = devm_regulator_get_enable(dev, "vdig");
+	if (ret)
+		return ret;
+
+	gpio_reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(gpio_reset))
+		return dev_err_probe(dev, PTR_ERR(gpio_reset),
+				     "Failed to get GPIO reset pin\n");
+
+	ret = lmp92064_reset(priv, gpio_reset);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to reset device\n");
+
+	indio_dev->name = "lmp92064";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = lmp92064_adc_channels;
+	indio_dev->num_channels = ARRAY_SIZE(lmp92064_adc_channels);
+	indio_dev->info = &lmp92064_adc_info;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct spi_device_id lmp92064_id_table[] = {
+	{ "lmp92064" },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, lmp92064_id_table);
+
+static const struct of_device_id lmp92064_of_table[] = {
+	{ .compatible = "ti,lmp92064" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, lmp92064_of_table);
+
+static struct spi_driver lmp92064_adc_driver = {
+	.driver = {
+		.name = "lmp92064",
+		.of_match_table = lmp92064_of_table,
+	},
+	.probe = lmp92064_adc_probe,
+	.id_table = lmp92064_id_table,
+};
+module_spi_driver(lmp92064_adc_driver);
+
+MODULE_AUTHOR("Leonard Göhrs <[e-mail]>");
+MODULE_DESCRIPTION("TI LMP92064 ADC");
+MODULE_LICENSE("GPL");