iio: adc: add support for ADC0831/ADC0832/ADC0834/ADC0838 chips

This adds ADC0831/ADC0832/ADC0834/ADC0838 8-bit ADC driver.
I have tested with ADC0831 and ADC0832.  The remaining ADC0834 and
ADC0838 are very similar to ADC0832.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/ti-adc0832.txt

+* Texas Instruments' ADC0831/ADC0832/ADC0832/ADC0838
+
+Required properties:
+ - compatible: Should be one of
+	* "ti,adc0831"
+	* "ti,adc0832"
+	* "ti,adc0834"
+	* "ti,adc0838"
+ - reg: spi chip select number for the device
+ - vref-supply: The regulator supply for ADC reference voltage
+ - spi-max-frequency: Max SPI frequency to use (< 400000)
+
+Example:
+adc@0 {
+	compatible = "ti,adc0832";
+	reg = <0>;
+	vref-supply = <&vdd_supply>;
+	spi-max-frequency = <200000>;
+};

drivers/iio/adc/Kconfig

@@ -360,6 +360,16 @@ config TI_ADC081C
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-adc081c.
 
+config TI_ADC0832
+	tristate "Texas Instruments ADC0831/ADC0832/ADC0834/ADC0838"
+	depends on SPI
+	help
+	  If you say yes here you get support for Texas Instruments ADC0831,
+	  ADC0832, ADC0834, ADC0838 ADC chips.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called ti-adc0832.
+
 config TI_ADC128S052
 	tristate "Texas Instruments ADC128S052/ADC122S021/ADC124S021"
 	depends on SPI

drivers/iio/adc/Makefile

@@ -35,6 +35,7 @@ obj-$(CONFIG_QCOM_SPMI_IADC) += qcom-spmi-iadc.o
 obj-$(CONFIG_QCOM_SPMI_VADC) += qcom-spmi-vadc.o
 obj-$(CONFIG_ROCKCHIP_SARADC) += rockchip_saradc.o
 obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
+obj-$(CONFIG_TI_ADC0832) += ti-adc0832.o
 obj-$(CONFIG_TI_ADC128S052) += ti-adc128s052.o
 obj-$(CONFIG_TI_ADS8688) += ti-ads8688.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o

drivers/iio/adc/ti-adc0832.c

+/*
+ * ADC0831/ADC0832/ADC0834/ADC0838 8-bit ADC driver
+ *
+ * Copyright (c) 2016 Akinobu Mita <akinobu.mita@gmail.com>
+ *
+ * This file is subject to the terms and conditions of version 2 of
+ * the GNU General Public License.  See the file COPYING in the main
+ * directory of this archive for more details.
+ *
+ * Datasheet: http://www.ti.com/lit/ds/symlink/adc0832-n.pdf
+ */
+
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/iio/iio.h>
+#include <linux/regulator/consumer.h>
+
+enum {
+	adc0831,
+	adc0832,
+	adc0834,
+	adc0838,
+};
+
+struct adc0832 {
+	struct spi_device *spi;
+	struct regulator *reg;
+	struct mutex lock;
+	u8 mux_bits;
+
+	u8 tx_buf[2] ____cacheline_aligned;
+	u8 rx_buf[2];
+};
+
+#define ADC0832_VOLTAGE_CHANNEL(chan)					\
+	{								\
+		.type = IIO_VOLTAGE,					\
+		.indexed = 1,						\
+		.channel = chan,					\
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)	\
+	}
+
+#define ADC0832_VOLTAGE_CHANNEL_DIFF(chan1, chan2)			\
+	{								\
+		.type = IIO_VOLTAGE,					\
+		.indexed = 1,						\
+		.channel = (chan1),					\
+		.channel2 = (chan2),					\
+		.differential = 1,					\
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)	\
+	}
+
+static const struct iio_chan_spec adc0831_channels[] = {
+	ADC0832_VOLTAGE_CHANNEL_DIFF(0, 1),
+};
+
+static const struct iio_chan_spec adc0832_channels[] = {
+	ADC0832_VOLTAGE_CHANNEL(0),
+	ADC0832_VOLTAGE_CHANNEL(1),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(0, 1),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(1, 0),
+};
+
+static const struct iio_chan_spec adc0834_channels[] = {
+	ADC0832_VOLTAGE_CHANNEL(0),
+	ADC0832_VOLTAGE_CHANNEL(1),
+	ADC0832_VOLTAGE_CHANNEL(2),
+	ADC0832_VOLTAGE_CHANNEL(3),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(0, 1),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(1, 0),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(2, 3),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(3, 2),
+};
+
+static const struct iio_chan_spec adc0838_channels[] = {
+	ADC0832_VOLTAGE_CHANNEL(0),
+	ADC0832_VOLTAGE_CHANNEL(1),
+	ADC0832_VOLTAGE_CHANNEL(2),
+	ADC0832_VOLTAGE_CHANNEL(3),
+	ADC0832_VOLTAGE_CHANNEL(4),
+	ADC0832_VOLTAGE_CHANNEL(5),
+	ADC0832_VOLTAGE_CHANNEL(6),
+	ADC0832_VOLTAGE_CHANNEL(7),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(0, 1),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(1, 0),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(2, 3),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(3, 2),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(4, 5),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(5, 4),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(6, 7),
+	ADC0832_VOLTAGE_CHANNEL_DIFF(7, 6),
+};
+
+static int adc0831_adc_conversion(struct adc0832 *adc)
+{
+	struct spi_device *spi = adc->spi;
+	int ret;
+
+	ret = spi_read(spi, &adc->rx_buf, 2);
+	if (ret)
+		return ret;
+
+	/*
+	 * Skip TRI-STATE and a leading zero
+	 */
+	return (adc->rx_buf[0] << 2 & 0xff) | (adc->rx_buf[1] >> 6);
+}
+
+static int adc0832_adc_conversion(struct adc0832 *adc, int channel,
+				bool differential)
+{
+	struct spi_device *spi = adc->spi;
+	struct spi_transfer xfer = {
+		.tx_buf = adc->tx_buf,
+		.rx_buf = adc->rx_buf,
+		.len = 2,
+	};
+	int ret;
+
+	if (!adc->mux_bits)
+		return adc0831_adc_conversion(adc);
+
+	/* start bit */
+	adc->tx_buf[0] = 1 << (adc->mux_bits + 1);
+	/* single-ended or differential */
+	adc->tx_buf[0] |= differential ? 0 : (1 << adc->mux_bits);
+	/* odd / sign */
+	adc->tx_buf[0] |= (channel % 2) << (adc->mux_bits - 1);
+	/* select */
+	if (adc->mux_bits > 1)
+		adc->tx_buf[0] |= channel / 2;
+
+	/* align Data output BIT7 (MSB) to 8-bit boundary */
+	adc->tx_buf[0] <<= 1;
+
+	ret = spi_sync_transfer(spi, &xfer, 1);
+	if (ret)
+		return ret;
+
+	return adc->rx_buf[1];
+}
+
+static int adc0832_read_raw(struct iio_dev *iio,
+			struct iio_chan_spec const *channel, int *value,
+			int *shift, long mask)
+{
+	struct adc0832 *adc = iio_priv(iio);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&adc->lock);
+		*value = adc0832_adc_conversion(adc, channel->channel,
+						channel->differential);
+		mutex_unlock(&adc->lock);
+		if (*value < 0)
+			return *value;
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*value = regulator_get_voltage(adc->reg);
+		if (*value < 0)
+			return *value;
+
+		/* convert regulator output voltage to mV */
+		*value /= 1000;
+		*shift = 8;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+	}
+
+	return -EINVAL;
+}
+
+static const struct iio_info adc0832_info = {
+	.read_raw = adc0832_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int adc0832_probe(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev;
+	struct adc0832 *adc;
+	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;
+	mutex_init(&adc->lock);
+
+	indio_dev->name = spi_get_device_id(spi)->name;
+	indio_dev->dev.parent = &spi->dev;
+	indio_dev->info = &adc0832_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	switch (spi_get_device_id(spi)->driver_data) {
+	case adc0831:
+		adc->mux_bits = 0;
+		indio_dev->channels = adc0831_channels;
+		indio_dev->num_channels = ARRAY_SIZE(adc0831_channels);
+		break;
+	case adc0832:
+		adc->mux_bits = 1;
+		indio_dev->channels = adc0832_channels;
+		indio_dev->num_channels = ARRAY_SIZE(adc0832_channels);
+		break;
+	case adc0834:
+		adc->mux_bits = 2;
+		indio_dev->channels = adc0834_channels;
+		indio_dev->num_channels = ARRAY_SIZE(adc0834_channels);
+		break;
+	case adc0838:
+		adc->mux_bits = 3;
+		indio_dev->channels = adc0838_channels;
+		indio_dev->num_channels = ARRAY_SIZE(adc0838_channels);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	adc->reg = devm_regulator_get(&spi->dev, "vref");
+	if (IS_ERR(adc->reg))
+		return PTR_ERR(adc->reg);
+
+	ret = regulator_enable(adc->reg);
+	if (ret)
+		return ret;
+
+	spi_set_drvdata(spi, indio_dev);
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		regulator_disable(adc->reg);
+
+	return ret;
+}
+
+static int adc0832_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = spi_get_drvdata(spi);
+	struct adc0832 *adc = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+	regulator_disable(adc->reg);
+
+	return 0;
+}
+
+#ifdef CONFIG_OF
+
+static const struct of_device_id adc0832_dt_ids[] = {
+	{ .compatible = "ti,adc0831", },
+	{ .compatible = "ti,adc0832", },
+	{ .compatible = "ti,adc0834", },
+	{ .compatible = "ti,adc0838", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, adc0832_dt_ids);
+
+#endif
+
+static const struct spi_device_id adc0832_id[] = {
+	{ "adc0831", adc0831 },
+	{ "adc0832", adc0832 },
+	{ "adc0834", adc0834 },
+	{ "adc0838", adc0838 },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, adc0832_id);
+
+static struct spi_driver adc0832_driver = {
+	.driver = {
+		.name = "adc0832",
+		.of_match_table = of_match_ptr(adc0832_dt_ids),
+	},
+	.probe = adc0832_probe,
+	.remove = adc0832_remove,
+	.id_table = adc0832_id,
+};
+module_spi_driver(adc0832_driver);
+
+MODULE_AUTHOR("Akinobu Mita <akinobu.mita@gmail.com>");
+MODULE_DESCRIPTION("ADC0831/ADC0832/ADC0834/ADC0838 driver");
+MODULE_LICENSE("GPL v2");