iio: temperature: add support for Maxim thermocouple chips

Add initial driver support for MAX6675, and MAX31855 thermocouple chips.

Cc: Marek Vasut <marex@denx.de>
Cc: Matt Porter <mporter@konsulko.com>
Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/temperature/maxim_thermocouple.txt

+Maxim thermocouple support
+
+* https://datasheets.maximintegrated.com/en/ds/MAX6675.pdf
+* https://datasheets.maximintegrated.com/en/ds/MAX31855.pdf
+
+Required properties:
+
+	- compatible: must be "maxim,max31855" or "maxim,max6675"
+	- reg: SPI chip select number for the device
+	- spi-max-frequency: must be 4300000
+	- spi-cpha: must be defined for max6675 to enable SPI mode 1
+
+	Refer to spi/spi-bus.txt for generic SPI slave bindings.
+
+Example:
+
+	max31855@0 {
+		compatible = "maxim,max31855";
+		reg = <0>;
+		spi-max-frequency = <4300000>;
+	};

drivers/iio/temperature/Kconfig

@@ -3,6 +3,20 @@
 #
 menu "Temperature sensors"
 
+config MAXIM_THERMOCOUPLE
+	tristate "Maxim thermocouple sensors"
+	depends on SPI
+	help
+	  If you say yes here you get support for the Maxim series of
+	  thermocouple sensors connected via SPI.
+
+	  Supported sensors:
+	   * MAX6675
+	   * MAX31855
+
+	  This driver can also be built as a module. If so, the module will
+	  be called maxim_thermocouple.
+
 config MLX90614
 	tristate "MLX90614 contact-less infrared sensor"
 	depends on I2C

drivers/iio/temperature/Makefile

@@ -2,6 +2,7 @@
 # Makefile for industrial I/O temperature drivers
 #
 
+obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
 obj-$(CONFIG_MLX90614) += mlx90614.o
 obj-$(CONFIG_TMP006) += tmp006.o
 obj-$(CONFIG_TSYS01) += tsys01.o

drivers/iio/temperature/maxim_thermocouple.c

+/*
+ * maxim_thermocouple.c  - Support for Maxim thermocouple chips
+ *
+ * Copyright (C) 2016 Matt Ranostay <mranostay@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+#include <linux/err.h>
+#include <linux/spi/spi.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/trigger.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
+
+#define MAXIM_THERMOCOUPLE_DRV_NAME	"maxim_thermocouple"
+
+enum {
+	MAX6675,
+	MAX31855,
+};
+
+const struct iio_chan_spec max6675_channels[] = {
+	{	/* thermocouple temperature */
+		.type = IIO_TEMP,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.scan_index = 0,
+		.scan_type = {
+			.sign = 's',
+			.realbits = 13,
+			.storagebits = 16,
+			.shift = 3,
+			.endianness = IIO_BE,
+		},
+	},
+	IIO_CHAN_SOFT_TIMESTAMP(1),
+};
+
+const struct iio_chan_spec max31855_channels[] = {
+	{	/* thermocouple temperature */
+		.type = IIO_TEMP,
+		.address = 2,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.scan_index = 0,
+		.scan_type = {
+			.sign = 's',
+			.realbits = 14,
+			.storagebits = 16,
+			.shift = 2,
+			.endianness = IIO_BE,
+		},
+	},
+	{	/* cold junction temperature */
+		.type = IIO_TEMP,
+		.address = 0,
+		.channel2 = IIO_MOD_TEMP_AMBIENT,
+		.modified = 1,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+		.scan_index = 1,
+		.scan_type = {
+			.sign = 's',
+			.realbits = 12,
+			.storagebits = 16,
+			.shift = 4,
+			.endianness = IIO_BE,
+		},
+	},
+	IIO_CHAN_SOFT_TIMESTAMP(2),
+};
+
+static const unsigned long max31855_scan_masks[] = {0x3, 0};
+
+struct maxim_thermocouple_chip {
+	const struct iio_chan_spec *channels;
+	const unsigned long *scan_masks;
+	u8 num_channels;
+	u8 read_size;
+
+	/* bit-check for valid input */
+	u32 status_bit;
+};
+
+const struct maxim_thermocouple_chip maxim_thermocouple_chips[] = {
+	[MAX6675] = {
+			.channels = max6675_channels,
+			.num_channels = ARRAY_SIZE(max6675_channels),
+			.read_size = 2,
+			.status_bit = BIT(2),
+		},
+	[MAX31855] = {
+			.channels = max31855_channels,
+			.num_channels = ARRAY_SIZE(max31855_channels),
+			.read_size = 4,
+			.scan_masks = max31855_scan_masks,
+			.status_bit = BIT(16),
+		},
+};
+
+struct maxim_thermocouple_data {
+	struct spi_device *spi;
+	const struct maxim_thermocouple_chip *chip;
+
+	u8 buffer[16] ____cacheline_aligned;
+};
+
+static int maxim_thermocouple_read(struct maxim_thermocouple_data *data,
+				   struct iio_chan_spec const *chan, int *val)
+{
+	unsigned int storage_bytes = data->chip->read_size;
+	unsigned int shift = chan->scan_type.shift + (chan->address * 8);
+	unsigned int buf;
+	int ret;
+
+	ret = spi_read(data->spi, (void *) &buf, storage_bytes);
+	if (ret)
+		return ret;
+
+	switch (storage_bytes) {
+	case 2:
+		*val = be16_to_cpu(buf);
+		break;
+	case 4:
+		*val = be32_to_cpu(buf);
+		break;
+	}
+
+	/* check to be sure this is a valid reading */
+	if (*val & data->chip->status_bit)
+		return -EINVAL;
+
+	*val = sign_extend32(*val >> shift, chan->scan_type.realbits - 1);
+
+	return 0;
+}
+
+static irqreturn_t maxim_thermocouple_trigger_handler(int irq, void *private)
+{
+	struct iio_poll_func *pf = private;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct maxim_thermocouple_data *data = iio_priv(indio_dev);
+	int ret;
+
+	ret = spi_read(data->spi, data->buffer, data->chip->read_size);
+	if (!ret) {
+		iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
+						   iio_get_time_ns(indio_dev));
+	}
+
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
+static int maxim_thermocouple_read_raw(struct iio_dev *indio_dev,
+				       struct iio_chan_spec const *chan,
+				       int *val, int *val2, long mask)
+{
+	struct maxim_thermocouple_data *data = iio_priv(indio_dev);
+	int ret = -EINVAL;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret)
+			return ret;
+
+		ret = maxim_thermocouple_read(data, chan, val);
+		iio_device_release_direct_mode(indio_dev);
+
+		if (!ret)
+			return IIO_VAL_INT;
+
+		break;
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->channel2) {
+		case IIO_MOD_TEMP_AMBIENT:
+			*val = 62;
+			*val2 = 500000; /* 1000 * 0.0625 */
+			ret = IIO_VAL_INT_PLUS_MICRO;
+			break;
+		default:
+			*val = 250; /* 1000 * 0.25 */
+			ret = IIO_VAL_INT;
+		};
+		break;
+	}
+
+	return ret;
+}
+
+static const struct iio_info maxim_thermocouple_info = {
+	.driver_module = THIS_MODULE,
+	.read_raw = maxim_thermocouple_read_raw,
+};
+
+static int maxim_thermocouple_probe(struct spi_device *spi)
+{
+	const struct spi_device_id *id = spi_get_device_id(spi);
+	struct iio_dev *indio_dev;
+	struct maxim_thermocouple_data *data;
+	const struct maxim_thermocouple_chip *chip =
+			&maxim_thermocouple_chips[id->driver_data];
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	indio_dev->info = &maxim_thermocouple_info;
+	indio_dev->name = MAXIM_THERMOCOUPLE_DRV_NAME;
+	indio_dev->channels = chip->channels;
+	indio_dev->available_scan_masks = chip->scan_masks;
+	indio_dev->num_channels = chip->num_channels;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	data = iio_priv(indio_dev);
+	data->spi = spi;
+	data->chip = chip;
+
+	ret = iio_triggered_buffer_setup(indio_dev, NULL,
+				maxim_thermocouple_trigger_handler, NULL);
+	if (ret)
+		return ret;
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		goto error_unreg_buffer;
+
+	return 0;
+
+error_unreg_buffer:
+	iio_triggered_buffer_cleanup(indio_dev);
+
+	return ret;
+}
+
+static int maxim_thermocouple_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = spi_get_drvdata(spi);
+
+	iio_device_unregister(indio_dev);
+	iio_triggered_buffer_cleanup(indio_dev);
+
+	return 0;
+}
+
+static const struct spi_device_id maxim_thermocouple_id[] = {
+	{"max6675", MAX6675},
+	{"max31855", MAX31855},
+	{},
+};
+MODULE_DEVICE_TABLE(spi, maxim_thermocouple_id);
+
+static struct spi_driver maxim_thermocouple_driver = {
+	.driver = {
+		.name	= MAXIM_THERMOCOUPLE_DRV_NAME,
+	},
+	.probe		= maxim_thermocouple_probe,
+	.remove		= maxim_thermocouple_remove,
+	.id_table	= maxim_thermocouple_id,
+};
+module_spi_driver(maxim_thermocouple_driver);
+
+MODULE_AUTHOR("Matt Ranostay <mranostay@gmail.com>");
+MODULE_DESCRIPTION("Maxim thermocouple sensors");
+MODULE_LICENSE("GPL");