[PATCH 2/2] iio: spi-dac: Add driver for SPI shift register DACs

[Mike Looijmans]

Add a driver for generic serial shift register DACs like TI DAC714.

Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>

---

 drivers/iio/dac/Kconfig   |  11 ++
 drivers/iio/dac/Makefile  |   1 +
 drivers/iio/dac/spi-dac.c | 212 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 224 insertions(+)
 create mode 100644 drivers/iio/dac/spi-dac.c

diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
index 93b8be183de6..bb35d901ee57 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -410,6 +410,17 @@ config MCP4922
 	  To compile this driver as a module, choose M here: the module
 	  will be called mcp4922.
 
+config SPI_DAC
+	tristate "SPI shift register DAC driver"
+	depends on SPI
+	help
+	  Driver for an array of shift-register DACs, like the TI DAC714.
+	  The driver shifts the DAC values into the registers in a SPI
+	  transfer, then optionally toggles a GPIO to latch the values.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called spi-dac.
+
 config STM32_DAC
 	tristate "STMicroelectronics STM32 DAC"
 	depends on (ARCH_STM32 && OF) || COMPILE_TEST
diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
index 5b2bac900d5a..33748799b0f0 100644
--- a/drivers/iio/dac/Makefile
+++ b/drivers/iio/dac/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_MCP4728) += mcp4728.o
 obj-$(CONFIG_MCP4922) += mcp4922.o
 obj-$(CONFIG_STM32_DAC_CORE) += stm32-dac-core.o
 obj-$(CONFIG_STM32_DAC) += stm32-dac.o
+obj-$(CONFIG_SPI_DAC) += spi-dac.o
 obj-$(CONFIG_TI_DAC082S085) += ti-dac082s085.o
 obj-$(CONFIG_TI_DAC5571) += ti-dac5571.o
 obj-$(CONFIG_TI_DAC7311) += ti-dac7311.o
diff --git a/drivers/iio/dac/spi-dac.c b/drivers/iio/dac/spi-dac.c
new file mode 100644
index 000000000000..0c0113d51604
--- /dev/null
+++ b/drivers/iio/dac/spi-dac.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SPI generic shift register Serial input Digital-to-Analog Converter
+ * For example, TI DAC714
+ *
+ * Copyright 2023 Topic Embedded Systems
+ */
+#include <linux/delay.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/gpio/consumer.h>
+#include <linux/iio/iio.h>
+
+struct spidac {
+	struct spi_device *spi;
+	struct gpio_desc *loaddacs;
+	u8 *data; /* SPI buffer */
+	u32 data_size;
+	/* Protect the data buffer and update sequence */
+	struct mutex lock;
+};
+
+static int spidac_cmd_single(struct spidac *priv,
+			     const struct iio_chan_spec *chan, int val)
+{
+	u8 *data = priv->data + chan->address;
+	unsigned int bytes = chan->scan_type.storagebits >> 3;
+	int ret;
+	unsigned int i;
+
+	/* Write big-endian value into data */
+	data += bytes - 1;
+	for (i = 0; i < bytes; i++, val >>= 8, data--)
+		*data = val & 0xff;
+
+	ret = spi_write(priv->spi, priv->data, priv->data_size);
+	if (ret)
+		return ret;
+
+	gpiod_set_value(priv->loaddacs, 1);
+	udelay(1);
+	gpiod_set_value(priv->loaddacs, 0);
+
+	return 0;
+}
+
+static int spidac_decode(struct spidac *priv, const struct iio_chan_spec *chan)
+{
+	u8 *data = priv->data + chan->address;
+	unsigned int bytes = chan->scan_type.storagebits >> 3;
+	unsigned int i;
+	int val = 0;
+
+	/* Read big-endian value from data */
+	for (i = 0; i < bytes; i++, data++)
+		val = (val << 8) | *data;
+
+	return val;
+}
+
+static int spidac_read_raw(struct iio_dev *iio_dev,
+			    const struct iio_chan_spec *chan,
+			    int *val, int *val2, long mask)
+{
+	struct spidac *priv;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		priv = iio_priv(iio_dev);
+
+		mutex_lock(&priv->lock);
+		*val = spidac_decode(priv, chan);
+		mutex_unlock(&priv->lock);
+
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = 1;
+		return IIO_VAL_INT;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int spidac_write_raw(struct iio_dev *iio_dev,
+			     const struct iio_chan_spec *chan,
+			     int val, int val2, long mask)
+{
+	struct spidac *priv = iio_priv(iio_dev);
+	int ret;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	mutex_lock(&priv->lock);
+	ret = spidac_cmd_single(priv, chan, val);
+	mutex_unlock(&priv->lock);
+
+	return ret;
+}
+
+static const struct iio_info spidac_info = {
+	.read_raw = spidac_read_raw,
+	.write_raw = spidac_write_raw,
+};
+
+static int spidac_probe(struct spi_device *spi)
+{
+	struct iio_dev *iio_dev;
+	struct spidac *priv;
+	struct iio_chan_spec *channels;
+	struct gpio_desc *reset_gpio;
+	u32 num_channels;
+	u32 bits_per_channel;
+	u32 bytes_per_channel;
+	u32 i;
+
+	iio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*priv));
+	if (!iio_dev)
+		return -ENOMEM;
+
+	priv = iio_priv(iio_dev);
+	priv->loaddacs = devm_gpiod_get_optional(&spi->dev, "ldac",
+						 GPIOD_OUT_LOW);
+	if (IS_ERR(priv->loaddacs))
+		return PTR_ERR(priv->loaddacs);
+
+	reset_gpio = devm_gpiod_get_optional(&spi->dev, "reset",
+					     GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return PTR_ERR(reset_gpio);
+
+	priv->spi = spi;
+	spi_set_drvdata(spi, iio_dev);
+	num_channels = 1;
+	bits_per_channel = 16;
+
+	device_property_read_u32(&spi->dev, "num-channels", &num_channels);
+	device_property_read_u32(&spi->dev, "bits-per-channel",
+				 &bits_per_channel);
+	bytes_per_channel = DIV_ROUND_UP(bits_per_channel, 8);
+
+	channels = devm_kcalloc(&spi->dev, num_channels, sizeof(*channels),
+				GFP_KERNEL);
+	if (!channels)
+		return -ENOMEM;
+
+	priv->data_size = num_channels * bytes_per_channel;
+	priv->data = devm_kzalloc(&spi->dev, priv->data_size,
+				  GFP_KERNEL | GFP_DMA);
+	if (!priv->data)
+		return -ENOMEM;
+
+	for (i = 0; i < num_channels; i++) {
+		struct iio_chan_spec *chan = &channels[i];
+
+		chan->type = IIO_VOLTAGE;
+		chan->indexed = 1;
+		chan->output = 1;
+		chan->channel = i;
+		chan->address = i * bytes_per_channel;
+		chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+		chan->info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE);
+		chan->scan_type.sign = 's';
+		chan->scan_type.realbits = bits_per_channel;
+		chan->scan_type.storagebits = bits_per_channel;
+	}
+
+	iio_dev->info = &spidac_info;
+	iio_dev->modes = INDIO_DIRECT_MODE;
+	iio_dev->channels = channels;
+	iio_dev->num_channels = num_channels;
+	iio_dev->name = spi_get_device_id(spi)->name;
+
+	mutex_init(&priv->lock);
+
+	if (reset_gpio) {
+		udelay(1);
+		gpiod_set_value(reset_gpio, 0);
+	}
+
+	return devm_iio_device_register(&spi->dev, iio_dev);
+}
+
+static const struct spi_device_id spidac_id[] = {
+	{"spi-dac"},
+	{}
+};
+MODULE_DEVICE_TABLE(spi, spidac_id);
+
+static const struct of_device_id spidac_of_match[] = {
+	{ .compatible = "spi-dac" },
+	{ .compatible = "ti,dac714" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, spidac_of_match);
+
+static struct spi_driver spidac_driver = {
+	.driver = {
+		   .name = "spi-dac",
+		   .of_match_table = spidac_of_match,
+		   },
+	.probe = spidac_probe,
+	.id_table = spidac_id,
+};
+module_spi_driver(spidac_driver);
+
+MODULE_AUTHOR("Mike Looijmans <mike.looijmans@xxxxxxxx>");
+MODULE_DESCRIPTION("SPI shift register DAC driver");
+MODULE_LICENSE("GPL");
-- 
2.34.1


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


TOPIC Embedded Products B.V.
Materiaalweg 4, 5681 RJ Best
The Netherlands

T: +31 (0) 499 33 69 69
E: mike.looijmans@xxxxxxxx
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