iio: dac: Support ROHM BD79703 DAC

The ROHM BD79703 is a 6 channel digital to analog converter.

Based on the data-sheet examples the hardware would support setting the
DAC word without changing the actual output. The data-sheet is not too
specific on how the enabling the output of new voltage set by DAC
should be done - hence this is not implemented by the driver.

The BD79703 would also support two specific "PULL_DOWN" modes. These
aren't currently supported by the driver either.

Add a very basic support for controlling the channel outputs one-by-one.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/bc77d7b979ca28408a216f597082fcd94ec63be7.1734608215.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/Kconfig

@@ -348,6 +348,14 @@ config AD8801
 	  To compile this driver as a module choose M here: the module will be called
 	  ad8801.
 
+config BD79703
+	tristate "ROHM Semiconductor BD79703 DAC driver"
+	depends on SPI
+	select REGMAP_SPI
+	help
+	  Say yes here to build support for ROHM Semiconductor BD79703 Digital
+	  to Analog Converter (DAC).
+
 config CIO_DAC
 	tristate "Measurement Computing CIO-DAC IIO driver"
 	depends on X86 && (ISA_BUS || PC104)

drivers/iio/dac/Makefile

@@ -34,6 +34,7 @@ obj-$(CONFIG_AD8460) += ad8460.o
 obj-$(CONFIG_AD8801) += ad8801.o
 obj-$(CONFIG_AD9739A) += ad9739a.o
 obj-$(CONFIG_ADI_AXI_DAC) += adi-axi-dac.o
+obj-$(CONFIG_BD79703) += rohm-bd79703.o
 obj-$(CONFIG_CIO_DAC) += cio-dac.o
 obj-$(CONFIG_DPOT_DAC) += dpot-dac.o
 obj-$(CONFIG_DS4424) += ds4424.o

drivers/iio/dac/rohm-bd79703.c

@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * BD79703 ROHM Digital to Analog converter
+ *
+ * Copyright (c) 2024, ROHM Semiconductor.
+ */
+
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+#include <linux/iio/iio.h>
+
+#define BD79703_MAX_REGISTER 0xf
+#define BD79703_DAC_BITS 8
+#define BD79703_REG_OUT_ALL GENMASK(2, 0)
+
+/*
+ * The BD79703 uses 12-bit SPI commands. First four bits (high bits) define
+ * channel(s) which are operated on, and also the mode. The mode can be to set
+ * a DAC word only, or set DAC word and output. The data-sheet is not very
+ * specific on how a previously set DAC word can be 'taken in to use'. Thus
+ * this driver only uses the 'set DAC and output it' -mode.
+ *
+ * The BD79703 latches last 12-bits when the chip-select is toggled. Thus we
+ * can use 16-bit transfers which should be widely supported. To simplify this
+ * further, we treat the last 8 bits as a value, and first 8 bits as an
+ * address. This allows us to separate channels/mode by address and treat the
+ * 8-bit register value as DAC word. The highest 4 bits of address will be
+ * discarded when the transfer is latched.
+ */
+static const struct regmap_config bd79703_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = BD79703_MAX_REGISTER,
+	.cache_type = REGCACHE_RBTREE,
+};
+
+struct bd79703_data {
+	struct regmap *regmap;
+	int vfs;
+};
+
+static int bd79703_read_raw(struct iio_dev *idev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	struct bd79703_data *data = iio_priv(idev);
+
+	if (mask != IIO_CHAN_INFO_SCALE)
+		return -EINVAL;
+
+	*val = data->vfs / 1000;
+	*val2 = BD79703_DAC_BITS;
+
+	return IIO_VAL_FRACTIONAL_LOG2;
+}
+
+static int bd79703_write_raw(struct iio_dev *idev,
+			     struct iio_chan_spec const *chan, int val,
+			     int val2, long mask)
+{
+	struct bd79703_data *data = iio_priv(idev);
+
+	if (val < 0 || val >= 1 << BD79703_DAC_BITS)
+		return -EINVAL;
+
+	return regmap_write(data->regmap, chan->channel + 1, val);
+};
+
+static const struct iio_info bd79703_info = {
+	.read_raw = bd79703_read_raw,
+	.write_raw = bd79703_write_raw,
+};
+
+#define BD79703_CHAN(_chan) {					\
+	.type = IIO_VOLTAGE,					\
+	.indexed = 1,						\
+	.output = 1,						\
+	.channel = (_chan),					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+	.address = (_chan),					\
+}
+
+static const struct iio_chan_spec bd79703_channels[] = {
+	BD79703_CHAN(0),
+	BD79703_CHAN(1),
+	BD79703_CHAN(2),
+	BD79703_CHAN(3),
+	BD79703_CHAN(4),
+	BD79703_CHAN(5),
+};
+
+static int bd79703_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct bd79703_data *data;
+	struct iio_dev *idev;
+	int ret;
+
+	idev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!idev)
+		return -ENOMEM;
+
+	data = iio_priv(idev);
+
+	data->regmap = devm_regmap_init_spi(spi, &bd79703_regmap_config);
+	if (IS_ERR(data->regmap))
+		return dev_err_probe(dev, PTR_ERR(data->regmap),
+				     "Failed to initialize Regmap\n");
+
+	ret = devm_regulator_get_enable(dev, "vcc");
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable VCC\n");
+
+	ret = devm_regulator_get_enable_read_voltage(dev, "vfs");
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to get Vfs\n");
+
+	data->vfs = ret;
+	idev->channels = bd79703_channels;
+	idev->num_channels = ARRAY_SIZE(bd79703_channels);
+	idev->modes = INDIO_DIRECT_MODE;
+	idev->info = &bd79703_info;
+	idev->name = "bd79703";
+
+	/* Initialize all to output zero */
+	ret = regmap_write(data->regmap, BD79703_REG_OUT_ALL, 0);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(dev, idev);
+}
+
+static const struct spi_device_id bd79703_id[] = {
+	{ "bd79703", },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, bd79703_id);
+
+static const struct of_device_id bd79703_of_match[] = {
+	{ .compatible = "rohm,bd79703", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, bd79703_of_match);
+
+static struct spi_driver bd79703_driver = {
+	.driver = {
+		.name = "bd79703",
+		.of_match_table = bd79703_of_match,
+	},
+	.probe = bd79703_probe,
+	.id_table = bd79703_id,
+};
+module_spi_driver(bd79703_driver);
+
+MODULE_AUTHOR("Matti Vaittinen <mazziesaccount@gmail.com>");
+MODULE_DESCRIPTION("ROHM BD79703 DAC driver");
+MODULE_LICENSE("GPL");