[PATCH v3 2/2] iio: add driver for the TI DAC8554

[Nikolaus Schulz]

The TI DAC8554 is a quad-channel Digital-to-Analog Converter with an SPI
interface.

Changes in v3:
* Small fixes in the documentation of struct dac8554_state
* Replace some magic constants with macros
* Replace memset on powerdown state arrays with explicit loop
* If probing fails due to invalid DT data, return -EINVAL instead of
  -ENODEV
* Add driver dependency on regulator support
* Move regulator_get_voltage call from probe time to dac8554_read_raw
* Rename _(read|write)_raw argument "mask" to "info"
* Make iio_chan_spec variable static
* DT: add vendor prefix to device specific "address" property
* Whitespace fixes

Changes in v2:
* Use DMA-safe buffer for SPI transfer
* Normalize powerdown_mode name "hi-z" to "three_state" as per
  ABI/testing/sysfs-bus-iio
* Register device late in probe function
* Avoid powerdown broadcast update, which touches all DAC on the bus

Signed-off-by: Nikolaus Schulz <nikolaus.schulz@xxxxxxxxxxxxxxxxx>
---
 drivers/iio/dac/Kconfig      |  11 ++
 drivers/iio/dac/Makefile     |   1 +
 drivers/iio/dac/ti-dac8554.c | 381 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 393 insertions(+)
 create mode 100644 drivers/iio/dac/ti-dac8554.c

diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
index 2236ea2..d3b21c853b5 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -181,4 +181,15 @@ config MCP4922
 	  To compile this driver as a module, choose M here: the module
 	  will be called mcp4922.
 
+config TI_DAC8554
+	tristate "TI DAC8554 driver"
+	depends on SPI
+	depends on OF
+	depends on REGULATOR
+	help
+	  Say yes here to build the driver for the TI DAC8554.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ti-dac8554.
+
 endmenu
diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
index 52be7e1..b98d79a 100644
--- a/drivers/iio/dac/Makefile
+++ b/drivers/iio/dac/Makefile
@@ -20,3 +20,4 @@ obj-$(CONFIG_MAX517) += max517.o
 obj-$(CONFIG_MAX5821) += max5821.o
 obj-$(CONFIG_MCP4725) += mcp4725.o
 obj-$(CONFIG_MCP4922) += mcp4922.o
+obj-$(CONFIG_TI_DAC8554) += ti-dac8554.o
diff --git a/drivers/iio/dac/ti-dac8554.c b/drivers/iio/dac/ti-dac8554.c
new file mode 100644
index 0000000..84b9f42
--- /dev/null
+++ b/drivers/iio/dac/ti-dac8554.c
@@ -0,0 +1,381 @@
+/*
+ * TI DAC8554 Digital to Analog Converter SPI driver
+ *
+ * Copyright (C) 2014 Avionic Design GmbH
+ *
+ * Based on ad5446r_spi.c
+ * Copyright (C) 2010,2011 Analog Devices Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/spi/spi.h>
+#include <linux/regulator/consumer.h>
+#include <linux/module.h>
+#include <linux/iio/iio.h>
+#include <linux/of.h>
+
+#define DAC8554_DRIVERNAME			"ti-dac8554"
+#define DAC8554_DAC_CHANNELS			4
+#define DAC8554_DATABITS			16
+
+/* Load commands */
+#define DAC8554_CMD_STORE_DAC_N			0x0
+#define DAC8554_CMD_UPDATE_DAC_N		0x1
+#define DAC8554_CMD_STORE_DAC_N_UPDATE_ALL	0x2
+#define DAC8554_CMD_UPDATE_BROADCAST		0x3
+
+#define DAC8554_BROADCAST_USE_SRDATA		0x2
+
+/* Powerdown modes (PD1 | PD2 bits) */
+#define DAC8554_PWRDN_HIZ			0x0
+#define DAC8554_PWRDN_1K			0x1
+#define DAC8554_PWRDN_100K			0x2
+
+/* Input shift register composition */
+#define DAC8554_ADDR_TO_SR(addr)		((addr) << 22)
+#define DAC8554_CMD_TO_SR(cmd)			((cmd) << 20)
+#define DAC8554_CHAN_TO_SR(chan)		((chan) << 17)
+#define DAC8554_PWRDN_TO_SR(mode)		(BIT(16) | (mode) << 14)
+
+/**
+ * struct dac8554_state - driver instance specific data
+ * @spi:		SPI device
+ * @reg:		supply regulator
+ * @addr:		two-bit chip address
+ * @val:		channel data
+ * @powerdown:		channel powerdown flag
+ * @powerdown_mode:	channel powerdown mode
+ * @xfer:		SPI transfer buffer
+ */
+struct dac8554_state {
+	struct spi_device		*spi;
+	struct regulator		*reg;
+	unsigned			addr;
+	u16				val[DAC8554_DAC_CHANNELS];
+	bool				powerdown[DAC8554_DAC_CHANNELS];
+	u8				powerdown_mode[DAC8554_DAC_CHANNELS];
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	u8				xfer[3] ____cacheline_aligned;
+};
+
+static int dac8554_spi_write(struct dac8554_state *st,
+			     unsigned cmd,
+			     unsigned chan_addr,
+			     unsigned val)
+{
+	u32 data;
+
+	/*
+	 * The input shift register is 24 bits wide. The 8 MSB are
+	 * control bits, followed by 16 data bits.
+	 * The first two bits A1 and A0 address a DAC8554 chip.
+	 * The next two are the command bits, LD1 and LD0.
+	 * After a don't-care-bit, the next two bits select the channel.
+	 * The final control bit PD0 is a flag signalling if the data
+	 * bits encode a powerdown mode. We merge PD0 with the adjacent
+	 * data bits.
+	 */
+
+	if (cmd > 3 || chan_addr > 3 ||
+			(val > 0xffff && (val & ~DAC8554_PWRDN_TO_SR(3))))
+		return -EINVAL;
+
+	data = DAC8554_ADDR_TO_SR(st->addr) | DAC8554_CMD_TO_SR(cmd) |
+	       DAC8554_CHAN_TO_SR(chan_addr) | val;
+
+	st->xfer[0] = data >> 16;
+	st->xfer[1] = data >> 8;
+	st->xfer[2] = data;
+
+	return spi_write(st->spi, st->xfer, sizeof(st->xfer));
+}
+
+static int dac8554_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val,
+			    int *val2,
+			    long info)
+{
+	struct dac8554_state *st = iio_priv(indio_dev);
+	int voltage_uv;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		*val = st->val[chan->address];
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		voltage_uv = regulator_get_voltage(st->reg);
+		if (voltage_uv < 0)
+			return voltage_uv;
+		*val = voltage_uv / 1000;
+		*val2 = DAC8554_DATABITS;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	}
+	return -EINVAL;
+}
+
+static int dac8554_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val,
+			     int val2,
+			     long info)
+{
+	struct dac8554_state *st = iio_priv(indio_dev);
+	int err;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		if (val > 0xffff || val < 0)
+			return -EINVAL;
+
+		err = dac8554_spi_write(st, DAC8554_CMD_UPDATE_DAC_N,
+					chan->address, val);
+		if (err)
+			return err;
+
+		st->val[chan->address] = val;
+
+		/* By hw design, DAC updates automatically trigger powerup. */
+		st->powerdown[chan->address] = false;
+
+		return 0;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int dac8554_get_powerdown_mode(struct iio_dev *indio_dev,
+				      const struct iio_chan_spec *chan)
+{
+	struct dac8554_state *st = iio_priv(indio_dev);
+
+	return st->powerdown_mode[chan->address];
+}
+
+static int dac8554_set_powerdown_mode(struct iio_dev *indio_dev,
+				      const struct iio_chan_spec *chan,
+				      unsigned int mode)
+{
+	struct dac8554_state *st = iio_priv(indio_dev);
+
+	st->powerdown_mode[chan->address] = mode;
+
+	return 0;
+}
+
+static ssize_t dac8554_read_dac_powerdown(struct iio_dev *indio_dev,
+					  uintptr_t private,
+					  const struct iio_chan_spec *chan,
+					  char *buf)
+{
+	struct dac8554_state *st = iio_priv(indio_dev);
+
+	return sprintf(buf, "%d\n", st->powerdown[chan->address]);
+}
+
+static ssize_t dac8554_write_dac_powerdown(struct iio_dev *indio_dev,
+					   uintptr_t private,
+					   const struct iio_chan_spec *chan,
+					   const char *buf,
+					   size_t len)
+{
+	bool powerdown;
+	int ret;
+	struct dac8554_state *st = iio_priv(indio_dev);
+	u8 powerdown_mode;
+
+	ret = strtobool(buf, &powerdown);
+	if (ret)
+		return ret;
+
+	st->powerdown[chan->address] = powerdown;
+
+	if (powerdown) {
+		powerdown_mode = st->powerdown_mode[chan->address];
+		ret = dac8554_spi_write(st,
+					DAC8554_CMD_UPDATE_DAC_N,
+					chan->address,
+					DAC8554_PWRDN_TO_SR(powerdown_mode));
+	} else {
+		/* Load DAC with cached value. This triggers a powerup. */
+		ret = dac8554_spi_write(st,
+					DAC8554_CMD_UPDATE_DAC_N,
+					chan->address,
+					st->val[chan->address]);
+	}
+
+	if (ret)
+		return ret;
+
+	return len;
+}
+
+static int dac8554_powerdown(struct dac8554_state *st,
+			     u8 powerdown_mode)
+{
+	int chan, cmd, ret;
+
+	for (chan = DAC8554_DAC_CHANNELS - 1; chan >= 0; --chan) {
+		cmd = chan ? DAC8554_CMD_STORE_DAC_N
+			   : DAC8554_CMD_STORE_DAC_N_UPDATE_ALL;
+		ret = dac8554_spi_write(st, cmd, chan,
+					DAC8554_PWRDN_TO_SR(powerdown_mode));
+		if (ret)
+			return ret;
+	}
+
+	for (chan = 0; chan < DAC8554_DAC_CHANNELS; ++chan) {
+		st->powerdown_mode[chan] = powerdown_mode;
+		st->powerdown[chan] = true;
+	}
+
+	return 0;
+}
+
+static const struct iio_info dac8554_info = {
+	.write_raw = dac8554_write_raw,
+	.read_raw = dac8554_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static const char * const dac8554_powerdown_modes[] = {
+	"three_state",
+	"1kohm_to_gnd",
+	"100kohm_to_gnd"
+};
+
+static const struct iio_enum dac8854_powerdown_mode_enum = {
+	.items = dac8554_powerdown_modes,
+	.num_items = ARRAY_SIZE(dac8554_powerdown_modes),
+	.get = dac8554_get_powerdown_mode,
+	.set = dac8554_set_powerdown_mode,
+};
+
+static const struct iio_chan_spec_ext_info dac8554_ext_info[] = {
+	{
+		.name = "powerdown",
+		.read = dac8554_read_dac_powerdown,
+		.write = dac8554_write_dac_powerdown,
+		.shared = IIO_SEPARATE,
+	},
+	IIO_ENUM("powerdown_mode", IIO_SEPARATE,
+		 &dac8854_powerdown_mode_enum),
+	IIO_ENUM_AVAILABLE("powerdown_mode", &dac8854_powerdown_mode_enum),
+	{ },
+};
+
+#define DAC8554_CHANNEL(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), \
+	.ext_info = dac8554_ext_info, \
+}
+static const struct iio_chan_spec dac8554_channels[] = {
+	DAC8554_CHANNEL(0),
+	DAC8554_CHANNEL(1),
+	DAC8554_CHANNEL(2),
+	DAC8554_CHANNEL(3),
+};
+#undef DAC8554_CHANNEL
+
+static int dac8554_probe(struct spi_device *spi)
+{
+	struct dac8554_state *st;
+	struct iio_dev *indio_dev;
+	int ret;
+	u32 addr;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	indio_dev->dev.parent = &spi->dev;
+	indio_dev->name = DAC8554_DRIVERNAME;
+	indio_dev->info = &dac8554_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = dac8554_channels;
+	indio_dev->num_channels = ARRAY_SIZE(dac8554_channels);
+
+	spi_set_drvdata(spi, indio_dev);
+
+	st = iio_priv(indio_dev);
+
+	if (!spi->dev.of_node) {
+		dev_err(&spi->dev, "missing OF node");
+		return -EINVAL;
+	}
+	ret = of_property_read_u32(spi->dev.of_node, "ti,address", &addr);
+	if (ret || addr < 0 || addr > 2) {
+		dev_err(&spi->dev, "no or invalid chip address");
+		return -EINVAL;
+	}
+
+	st->spi = spi;
+	st->addr = addr;
+
+	st->reg = devm_regulator_get(&spi->dev, "vref");
+	if (IS_ERR(st->reg))
+		return PTR_ERR(st->reg);
+
+	ret = regulator_enable(st->reg);
+	if (ret)
+		return ret;
+
+	ret = dac8554_powerdown(st, DAC8554_PWRDN_100K);
+	if (ret)
+		goto error_disable_reg;
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		goto error_disable_reg;
+
+	return 0;
+
+error_disable_reg:
+	regulator_disable(st->reg);
+	return ret;
+}
+
+static int dac8554_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = spi_get_drvdata(spi);
+	struct dac8554_state *st = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+	regulator_disable(st->reg);
+
+	return 0;
+}
+
+static const struct of_device_id dac8554_of_match[] = {
+	{ .compatible = "ti,dac8554" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, dac8554_of_match);
+
+static struct spi_driver dac8554_driver = {
+	.driver = {
+		.name = DAC8554_DRIVERNAME,
+		.owner = THIS_MODULE,
+		.of_match_table = dac8554_of_match,
+	 },
+	.probe = dac8554_probe,
+	.remove = dac8554_remove,
+};
+module_spi_driver(dac8554_driver);
+
+MODULE_AUTHOR("Nikolaus Schulz <nikolaus.schulz@xxxxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Texas Instruments DAC8554 SPI driver");
+MODULE_LICENSE("GPL v2");
-- 
2.1.3

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