iio: dac: driver for MCP4821

Adds driver for the MCP48xx series of DACs.

Device uses a simplex SPI channel. To set the value of an output channel,
a 16-bit data of following format must be written:

Bit field | Description
15 [MSB] | Channel selection bit
0 -> Channel A
1 -> Channel B
13 | Output Gain Selection bit
0 -> 2x Gain (Vref = 4.096V)
1 -> 1x Gain (Vref = 2.048V)
12 | Output Shutdown Control bit
0 -> Shutdown the selected channel
1 -> Active mode operation
11-0 [LSB]| DAC Input Data bits
Value's big endian representation is taken as input for the
selected DAC channel. For devices with a resolution of less
than 12-bits, only the x most significant bits are considered
where x is the resolution of the device.
Reference: Page#22 [MCP48x2 Datasheet]

Supported devices:
+---------+--------------+-------------+
| Device | Resolution | Channels |
|---------|--------------|-------------|
| MCP4801 | 8-bit | 1 |
| MCP4802 | 8-bit | 2 |
| MCP4811 | 10-bit | 1 |
| MCP4812 | 10-bit | 2 |
| MCP4821 | 12-bit | 1 |
| MCP4822 | 12-bit | 2 |
+---------+--------------+-------------+

Devices tested:
MCP4821 [12-bit single channel]
MCP4802 [8-bit dual channel]

Tested on Raspberry Pi Zero 2W

Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/22244B.pdf #MCP48x1
Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf #MCP48x2
Signed-off-by: Anshul Dalal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 F:	drivers/iio/potentiometer/mcp4018.c
 F:	drivers/iio/potentiometer/mcp4531.c
 
+MCP4821 DAC DRIVER
+M:	Anshul Dalal <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/dac/microchip,mcp4821.yaml
+F:	drivers/iio/dac/mcp4821.c
+
 MCR20A IEEE-802.15.4 RADIO DRIVER
 M:	Stefan Schmidt <[e-mail]>
 L:	[e-mail]

drivers/iio/dac/Kconfig

···
 	  To compile this driver as a module, choose M here: the module
 	  will be called mcp4728.
 
+config MCP4821
+	tristate "MCP4801/02/11/12/21/22 DAC driver"
+	depends on SPI
+	help
+	  Say yes here to build the driver for the Microchip MCP4801
+	  MCP4802, MCP4811, MCP4812, MCP4821 and MCP4822 DAC devices.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called mcp4821.
+
 config MCP4922
 	tristate "MCP4902, MCP4912, MCP4922 DAC driver"
 	depends on SPI

drivers/iio/dac/Makefile

···
 obj-$(CONFIG_MAX5821) += max5821.o
 obj-$(CONFIG_MCP4725) += mcp4725.o
 obj-$(CONFIG_MCP4728) += mcp4728.o
+obj-$(CONFIG_MCP4821) += mcp4821.o
 obj-$(CONFIG_MCP4922) += mcp4922.o
 obj-$(CONFIG_STM32_DAC_CORE) += stm32-dac-core.o
 obj-$(CONFIG_STM32_DAC) += stm32-dac.o

drivers/iio/dac/mcp4821.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023 Anshul Dalal <[e-mail]>
+ *
+ * Driver for Microchip MCP4801, MCP4802, MCP4811, MCP4812, MCP4821 and MCP4822
+ *
+ * Based on the work of:
+ *	Michael Welling (MCP4922 Driver)
+ *
+ * Datasheet:
+ *	MCP48x1: https://ww1.microchip.com/downloads/en/DeviceDoc/22244B.pdf
+ *	MCP48x2: https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf
+ *
+ * TODO:
+ *	- Configurable gain
+ *	- Regulator control
+ */
+
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/spi/spi.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/types.h>
+
+#include <asm/unaligned.h>
+
+#define MCP4821_ACTIVE_MODE BIT(12)
+#define MCP4802_SECOND_CHAN BIT(15)
+
+/* DAC uses an internal Voltage reference of 4.096V at a gain of 2x */
+#define MCP4821_2X_GAIN_VREF_MV 4096
+
+enum mcp4821_supported_drvice_ids {
+	ID_MCP4801,
+	ID_MCP4802,
+	ID_MCP4811,
+	ID_MCP4812,
+	ID_MCP4821,
+	ID_MCP4822,
+};
+
+struct mcp4821_state {
+	struct spi_device *spi;
+	u16 dac_value[2];
+};
+
+struct mcp4821_chip_info {
+	const char *name;
+	int num_channels;
+	const struct iio_chan_spec channels[2];
+};
+
+#define MCP4821_CHAN(channel_id, resolution)                          \
+	{                                                             \
+		.type = IIO_VOLTAGE, .output = 1, .indexed = 1,       \
+		.channel = (channel_id),                              \
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),         \
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
+		.scan_type = {                                        \
+			.realbits = (resolution),                     \
+			.shift = 12 - (resolution),                   \
+		},                                                    \
+	}
+
+static const struct mcp4821_chip_info mcp4821_chip_info_table[6] = {
+	[ID_MCP4801] = {
+			.name = "mcp4801",
+			.num_channels = 1,
+			.channels = {
+				MCP4821_CHAN(0, 8),
+			},
+	},
+	[ID_MCP4802] = {
+			.name = "mcp4802",
+			.num_channels = 2,
+			.channels = {
+				MCP4821_CHAN(0, 8),
+				MCP4821_CHAN(1, 8),
+			},
+	},
+	[ID_MCP4811] = {
+			.name = "mcp4811",
+			.num_channels = 1,
+			.channels = {
+				MCP4821_CHAN(0, 10),
+			},
+	},
+	[ID_MCP4812] = {
+			.name = "mcp4812",
+			.num_channels = 2,
+			.channels = {
+				MCP4821_CHAN(0, 10),
+				MCP4821_CHAN(1, 10),
+			},
+	},
+	[ID_MCP4821] = {
+			.name = "mcp4821",
+			.num_channels = 1,
+			.channels = {
+				MCP4821_CHAN(0, 12),
+			},
+	},
+	[ID_MCP4822] = {
+			.name = "mcp4822",
+			.num_channels = 2,
+			.channels = {
+				MCP4821_CHAN(0, 12),
+				MCP4821_CHAN(1, 12),
+			},
+	},
+};
+
+static int mcp4821_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	struct mcp4821_state *state;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		state = iio_priv(indio_dev);
+		*val = state->dac_value[chan->channel];
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = MCP4821_2X_GAIN_VREF_MV;
+		*val2 = chan->scan_type.realbits;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int mcp4821_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int val,
+			     int val2, long mask)
+{
+	struct mcp4821_state *state = iio_priv(indio_dev);
+	u16 write_val;
+	__be16 write_buffer;
+	int ret;
+
+	if (val2 != 0)
+		return -EINVAL;
+
+	if (val < 0 || val >= BIT(chan->scan_type.realbits))
+		return -EINVAL;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	write_val = MCP4821_ACTIVE_MODE | val << chan->scan_type.shift;
+	if (chan->channel)
+		write_val |= MCP4802_SECOND_CHAN;
+
+	write_buffer = cpu_to_be16(write_val);
+	ret = spi_write(state->spi, &write_buffer, sizeof(write_buffer));
+	if (ret) {
+		dev_err(&state->spi->dev, "Failed to write to device: %d", ret);
+		return ret;
+	}
+
+	state->dac_value[chan->channel] = val;
+
+	return 0;
+}
+
+static const struct iio_info mcp4821_info = {
+	.read_raw = &mcp4821_read_raw,
+	.write_raw = &mcp4821_write_raw,
+};
+
+static int mcp4821_probe(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev;
+	struct mcp4821_state *state;
+	const struct mcp4821_chip_info *info;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*state));
+	if (indio_dev == NULL)
+		return -ENOMEM;
+
+	state = iio_priv(indio_dev);
+	state->spi = spi;
+
+	info = spi_get_device_match_data(spi);
+	indio_dev->name = info->name;
+	indio_dev->info = &mcp4821_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = info->channels;
+	indio_dev->num_channels = info->num_channels;
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+#define MCP4821_COMPATIBLE(of_compatible, id)        \
+	{                                            \
+		.compatible = of_compatible,         \
+		.data = &mcp4821_chip_info_table[id] \
+	}
+
+static const struct of_device_id mcp4821_of_table[] = {
+	MCP4821_COMPATIBLE("microchip,mcp4801", ID_MCP4801),
+	MCP4821_COMPATIBLE("microchip,mcp4802", ID_MCP4802),
+	MCP4821_COMPATIBLE("microchip,mcp4811", ID_MCP4811),
+	MCP4821_COMPATIBLE("microchip,mcp4812", ID_MCP4812),
+	MCP4821_COMPATIBLE("microchip,mcp4821", ID_MCP4821),
+	MCP4821_COMPATIBLE("microchip,mcp4822", ID_MCP4822),
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, mcp4821_of_table);
+
+static const struct spi_device_id mcp4821_id_table[] = {
+	{ "mcp4801", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4801]},
+	{ "mcp4802", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4802]},
+	{ "mcp4811", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4811]},
+	{ "mcp4812", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4812]},
+	{ "mcp4821", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4821]},
+	{ "mcp4822", (kernel_ulong_t)&mcp4821_chip_info_table[ID_MCP4822]},
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(spi, mcp4821_id_table);
+
+static struct spi_driver mcp4821_driver = {
+	.driver = {
+		.name = "mcp4821",
+		.of_match_table = mcp4821_of_table,
+	},
+	.probe = mcp4821_probe,
+	.id_table = mcp4821_id_table,
+};
+module_spi_driver(mcp4821_driver);
+
+MODULE_AUTHOR("Anshul Dalal <[e-mail]>");
+MODULE_DESCRIPTION("Microchip MCP4821 DAC Driver");
+MODULE_LICENSE("GPL");