iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

This adds a driver for the Analog Devices Inc. AD7944, AD7985, and
AD7986 ADCs. These are a family of pin-compatible ADCs that can sample
at rates up to 2.5 MSPS.

The initial driver adds support for sampling at lower rates using the
usual IIO triggered buffer and can handle all 3 possible reference
voltage configurations.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240304-ad7944-mainline-v5-2-f0a38cea8901@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -448,6 +448,7 @@ R:	David Lechner <dlechner@baylibre.com>
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
+F:	drivers/iio/adc/ad7944.c
 
 ADAFRUIT MINI I2C GAMEPAD
 M:	Anshul Dalal <anshulusr@gmail.com>

drivers/iio/adc/Kconfig

@@ -281,6 +281,16 @@ config AD7923
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad7923.
 
+config AD7944
+	tristate "Analog Devices AD7944 and similar ADCs driver"
+	depends on SPI
+	help
+	  Say yes here to build support for Analog Devices
+	  AD7944, AD7985, AD7986 ADCs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ad7944
+
 config AD7949
 	tristate "Analog Devices AD7949 and similar ADCs driver"
 	depends on SPI

drivers/iio/adc/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_AD7780) += ad7780.o
 obj-$(CONFIG_AD7791) += ad7791.o
 obj-$(CONFIG_AD7793) += ad7793.o
 obj-$(CONFIG_AD7887) += ad7887.o
+obj-$(CONFIG_AD7944) += ad7944.o
 obj-$(CONFIG_AD7949) += ad7949.o
 obj-$(CONFIG_AD799X) += ad799x.o
 obj-$(CONFIG_AD9467) += ad9467.o

drivers/iio/adc/ad7944.c

@@ -0,0 +1,416 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Analog Devices AD7944/85/86 PulSAR ADC family driver.
+ *
+ * Copyright 2024 Analog Devices, Inc.
+ * Copyright 2024 BayLibre, SAS
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/property.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+#include <linux/string_helpers.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/iio/trigger_consumer.h>
+#include <linux/iio/triggered_buffer.h>
+
+#define AD7944_INTERNAL_REF_MV		4096
+
+struct ad7944_timing_spec {
+	/* Normal mode max conversion time (t_{CONV}). */
+	unsigned int conv_ns;
+	/* TURBO mode max conversion time (t_{CONV}). */
+	unsigned int turbo_conv_ns;
+};
+
+struct ad7944_adc {
+	struct spi_device *spi;
+	/* Chip-specific timing specifications. */
+	const struct ad7944_timing_spec *timing_spec;
+	/* GPIO connected to CNV pin. */
+	struct gpio_desc *cnv;
+	/* Optional GPIO to enable turbo mode. */
+	struct gpio_desc *turbo;
+	/* Indicates TURBO is hard-wired to be always enabled. */
+	bool always_turbo;
+	/* Reference voltage (millivolts). */
+	unsigned int ref_mv;
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	struct {
+		union {
+			u16 u16;
+			u32 u32;
+		} raw;
+		u64 timestamp __aligned(8);
+	 } sample __aligned(IIO_DMA_MINALIGN);
+};
+
+static const struct ad7944_timing_spec ad7944_timing_spec = {
+	.conv_ns = 420,
+	.turbo_conv_ns = 320,
+};
+
+static const struct ad7944_timing_spec ad7986_timing_spec = {
+	.conv_ns = 500,
+	.turbo_conv_ns = 400,
+};
+
+struct ad7944_chip_info {
+	const char *name;
+	const struct ad7944_timing_spec *timing_spec;
+	const struct iio_chan_spec channels[2];
+};
+
+/*
+ * AD7944_DEFINE_CHIP_INFO - Define a chip info structure for a specific chip
+ * @_name: The name of the chip
+ * @_ts: The timing specification for the chip
+ * @_bits: The number of bits in the conversion result
+ * @_diff: Whether the chip is true differential or not
+ */
+#define AD7944_DEFINE_CHIP_INFO(_name, _ts, _bits, _diff)		\
+static const struct ad7944_chip_info _name##_chip_info = {		\
+	.name = #_name,							\
+	.timing_spec = &_ts##_timing_spec,				\
+	.channels = {							\
+		{							\
+			.type = IIO_VOLTAGE,				\
+			.indexed = 1,					\
+			.differential = _diff,				\
+			.channel = 0,					\
+			.channel2 = _diff ? 1 : 0,			\
+			.scan_index = 0,				\
+			.scan_type.sign = _diff ? 's' : 'u',		\
+			.scan_type.realbits = _bits,			\
+			.scan_type.storagebits = _bits > 16 ? 32 : 16,	\
+			.scan_type.endianness = IIO_CPU,		\
+			.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)	\
+					| BIT(IIO_CHAN_INFO_SCALE),	\
+		},							\
+		IIO_CHAN_SOFT_TIMESTAMP(1),				\
+	},								\
+}
+
+/* pseudo-differential with ground sense */
+AD7944_DEFINE_CHIP_INFO(ad7944, ad7944, 14, 0);
+AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 16, 0);
+/* fully differential */
+AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 18, 1);
+
+/*
+ * ad7944_4wire_mode_conversion - Perform a 4-wire mode conversion and acquisition
+ * @adc: The ADC device structure
+ * @chan: The channel specification
+ * Return: 0 on success, a negative error code on failure
+ *
+ * Upon successful return adc->sample.raw will contain the conversion result.
+ */
+static int ad7944_4wire_mode_conversion(struct ad7944_adc *adc,
+					const struct iio_chan_spec *chan)
+{
+	unsigned int t_conv_ns = adc->always_turbo ? adc->timing_spec->turbo_conv_ns
+						   : adc->timing_spec->conv_ns;
+	struct spi_transfer xfers[] = {
+		{
+			/*
+			 * NB: can get better performance from some SPI
+			 * controllers if we use the same bits_per_word
+			 * in every transfer.
+			 */
+			.bits_per_word = chan->scan_type.realbits,
+			/*
+			 * CS has to be high for full conversion time to avoid
+			 * triggering the busy indication.
+			 */
+			.cs_off = 1,
+			.delay = {
+				.value = t_conv_ns,
+				.unit = SPI_DELAY_UNIT_NSECS,
+			},
+
+		},
+		{
+			.rx_buf = &adc->sample.raw,
+			.len = BITS_TO_BYTES(chan->scan_type.storagebits),
+			.bits_per_word = chan->scan_type.realbits,
+		},
+	};
+	int ret;
+
+	/*
+	 * In 4-wire mode, the CNV line is held high for the entire conversion
+	 * and acquisition process.
+	 */
+	gpiod_set_value_cansleep(adc->cnv, 1);
+	ret = spi_sync_transfer(adc->spi, xfers, ARRAY_SIZE(xfers));
+	gpiod_set_value_cansleep(adc->cnv, 0);
+
+	return ret;
+}
+
+static int ad7944_single_conversion(struct ad7944_adc *adc,
+				    const struct iio_chan_spec *chan,
+				    int *val)
+{
+	int ret;
+
+	ret = ad7944_4wire_mode_conversion(adc, chan);
+	if (ret)
+		return ret;
+
+	if (chan->scan_type.storagebits > 16)
+		*val = adc->sample.raw.u32;
+	else
+		*val = adc->sample.raw.u16;
+
+	if (chan->scan_type.sign == 's')
+		*val = sign_extend32(*val, chan->scan_type.realbits - 1);
+
+	return IIO_VAL_INT;
+}
+
+static int ad7944_read_raw(struct iio_dev *indio_dev,
+			   const struct iio_chan_spec *chan,
+			   int *val, int *val2, long info)
+{
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+	int ret;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret)
+			return ret;
+
+		ret = ad7944_single_conversion(adc, chan, val);
+		iio_device_release_direct_mode(indio_dev);
+		return ret;
+
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = adc->ref_mv;
+
+			if (chan->scan_type.sign == 's')
+				*val2 = chan->scan_type.realbits - 1;
+			else
+				*val2 = chan->scan_type.realbits;
+
+			return IIO_VAL_FRACTIONAL_LOG2;
+		default:
+			return -EINVAL;
+		}
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ad7944_iio_info = {
+	.read_raw = &ad7944_read_raw,
+};
+
+static irqreturn_t ad7944_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+	int ret;
+
+	ret = ad7944_4wire_mode_conversion(adc, &indio_dev->channels[0]);
+	if (ret)
+		goto out;
+
+	iio_push_to_buffers_with_timestamp(indio_dev, &adc->sample.raw,
+					   pf->timestamp);
+
+out:
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
+static const char * const ad7944_power_supplies[] = {
+	"avdd",	"dvdd",	"bvdd", "vio"
+};
+
+static void ad7944_ref_disable(void *ref)
+{
+	regulator_disable(ref);
+}
+
+static int ad7944_probe(struct spi_device *spi)
+{
+	const struct ad7944_chip_info *chip_info;
+	struct device *dev = &spi->dev;
+	struct iio_dev *indio_dev;
+	struct ad7944_adc *adc;
+	bool have_refin = false;
+	struct regulator *ref;
+	int ret;
+
+	/*
+	 * driver currently only supports the conventional "4-wire" mode and
+	 * not other special wiring configurations.
+	 */
+	if (device_property_present(dev, "adi,spi-mode"))
+		return dev_err_probe(dev, -EINVAL,
+				     "adi,spi-mode is not currently supported\n");
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*adc));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	adc = iio_priv(indio_dev);
+	adc->spi = spi;
+
+	chip_info = spi_get_device_match_data(spi);
+	if (!chip_info)
+		return dev_err_probe(dev, -EINVAL, "no chip info\n");
+
+	adc->timing_spec = chip_info->timing_spec;
+
+	/*
+	 * Some chips use unusual word sizes, so check now instead of waiting
+	 * for the first xfer.
+	 */
+	if (!spi_is_bpw_supported(spi, chip_info->channels[0].scan_type.realbits))
+		return dev_err_probe(dev, -EINVAL,
+				"SPI host does not support %d bits per word\n",
+				chip_info->channels[0].scan_type.realbits);
+
+	ret = devm_regulator_bulk_get_enable(dev,
+					     ARRAY_SIZE(ad7944_power_supplies),
+					     ad7944_power_supplies);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to get and enable supplies\n");
+
+	/*
+	 * Sort out what is being used for the reference voltage. Options are:
+	 * - internal reference: neither REF or REFIN is connected
+	 * - internal reference with external buffer: REF not connected, REFIN
+	 *   is connected
+	 * - external reference: REF is connected, REFIN is not connected
+	 */
+
+	ref = devm_regulator_get_optional(dev, "ref");
+	if (IS_ERR(ref)) {
+		if (PTR_ERR(ref) != -ENODEV)
+			return dev_err_probe(dev, PTR_ERR(ref),
+					     "failed to get REF supply\n");
+
+		ref = NULL;
+	}
+
+	ret = devm_regulator_get_enable_optional(dev, "refin");
+	if (ret == 0)
+		have_refin = true;
+	else if (ret != -ENODEV)
+		return dev_err_probe(dev, ret,
+				     "failed to get and enable REFIN supply\n");
+
+	if (have_refin && ref)
+		return dev_err_probe(dev, -EINVAL,
+				     "cannot have both refin and ref supplies\n");
+
+	if (ref) {
+		ret = regulator_enable(ref);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "failed to enable REF supply\n");
+
+		ret = devm_add_action_or_reset(dev, ad7944_ref_disable, ref);
+		if (ret)
+			return ret;
+
+		ret = regulator_get_voltage(ref);
+		if (ret < 0)
+			return dev_err_probe(dev, ret,
+					     "failed to get REF voltage\n");
+
+		/* external reference */
+		adc->ref_mv = ret / 1000;
+	} else {
+		/* internal reference */
+		adc->ref_mv = AD7944_INTERNAL_REF_MV;
+	}
+
+	/*
+	 * CNV gpio is required in 4-wire mode which is the only currently
+	 * supported mode.
+	 */
+	adc->cnv = devm_gpiod_get(dev, "cnv", GPIOD_OUT_LOW);
+	if (IS_ERR(adc->cnv))
+		return dev_err_probe(dev, PTR_ERR(adc->cnv),
+				     "failed to get CNV GPIO\n");
+
+	adc->turbo = devm_gpiod_get_optional(dev, "turbo", GPIOD_OUT_LOW);
+	if (IS_ERR(adc->turbo))
+		return dev_err_probe(dev, PTR_ERR(adc->turbo),
+				     "failed to get TURBO GPIO\n");
+
+	adc->always_turbo = device_property_present(dev, "adi,always-turbo");
+
+	if (adc->turbo && adc->always_turbo)
+		return dev_err_probe(dev, -EINVAL,
+			"cannot have both turbo-gpios and adi,always-turbo\n");
+
+	indio_dev->name = chip_info->name;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &ad7944_iio_info;
+	indio_dev->channels = chip_info->channels;
+	indio_dev->num_channels = ARRAY_SIZE(chip_info->channels);
+
+	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+					      iio_pollfunc_store_time,
+					      ad7944_trigger_handler, NULL);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id ad7944_of_match[] = {
+	{ .compatible = "adi,ad7944", .data = &ad7944_chip_info },
+	{ .compatible = "adi,ad7985", .data = &ad7985_chip_info },
+	{ .compatible = "adi,ad7986", .data = &ad7986_chip_info },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ad7944_of_match);
+
+static const struct spi_device_id ad7944_spi_id[] = {
+	{ "ad7944", (kernel_ulong_t)&ad7944_chip_info },
+	{ "ad7985", (kernel_ulong_t)&ad7985_chip_info },
+	{ "ad7986", (kernel_ulong_t)&ad7986_chip_info },
+	{ }
+
+};
+MODULE_DEVICE_TABLE(spi, ad7944_spi_id);
+
+static struct spi_driver ad7944_driver = {
+	.driver = {
+		.name = "ad7944",
+		.of_match_table = ad7944_of_match,
+	},
+	.probe = ad7944_probe,
+	.id_table = ad7944_spi_id,
+};
+module_spi_driver(ad7944_driver);
+
+MODULE_AUTHOR("David Lechner <dlechner@baylibre.com>");
+MODULE_DESCRIPTION("Analog Devices AD7944 PulSAR ADC family driver");
+MODULE_LICENSE("GPL");