IIO: ADC: add sigma delta modulator support

Add generic driver to support sigma delta modulators.
Typically, this device is hardware connected to
an IIO device in charge of the conversion. Devices are
bonded through the hardware consumer API.

Signed-off-by: Arnaud Pouliquen <[e-mail]>
Acked-by: Jonathan Cameron <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/iio/adc/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called spear_adc.
 
+config SD_ADC_MODULATOR
+	tristate "Generic sigma delta modulator"
+	depends on OF
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Select this option to enables sigma delta modulator. This driver can
+	  support generic sigma delta modulators.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called sd_adc_modulator.
+
 config STM32_ADC_CORE
 	tristate "STMicroelectronics STM32 adc core"
 	depends on ARCH_STM32 || COMPILE_TEST

drivers/iio/adc/Makefile

···
 obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o
 xilinx-xadc-y := xilinx-xadc-core.o xilinx-xadc-events.o
 obj-$(CONFIG_XILINX_XADC) += xilinx-xadc.o
+obj-$(CONFIG_SD_ADC_MODULATOR) += sd_adc_modulator.o

drivers/iio/adc/sd_adc_modulator.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic sigma delta modulator driver
+ *
+ * Copyright (C) 2017, STMicroelectronics - All Rights Reserved
+ * Author: Arnaud Pouliquen <[e-mail]>.
+ */
+
+#include <linux/iio/iio.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+
+static const struct iio_info iio_sd_mod_iio_info;
+
+static const struct iio_chan_spec iio_sd_mod_ch = {
+	.type = IIO_VOLTAGE,
+	.indexed = 1,
+	.scan_type = {
+		.sign = 'u',
+		.realbits = 1,
+		.shift = 0,
+	},
+};
+
+static int iio_sd_mod_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct iio_dev *iio;
+
+	iio = devm_iio_device_alloc(dev, 0);
+	if (!iio)
+		return -ENOMEM;
+
+	iio->dev.parent = dev;
+	iio->dev.of_node = dev->of_node;
+	iio->name = dev_name(dev);
+	iio->info = &iio_sd_mod_iio_info;
+	iio->modes = INDIO_BUFFER_HARDWARE;
+
+	iio->num_channels = 1;
+	iio->channels = &iio_sd_mod_ch;
+
+	platform_set_drvdata(pdev, iio);
+
+	return devm_iio_device_register(&pdev->dev, iio);
+}
+
+static const struct of_device_id sd_adc_of_match[] = {
+	{ .compatible = "sd-modulator" },
+	{ .compatible = "ads1201" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, sd_adc_of_match);
+
+static struct platform_driver iio_sd_mod_adc = {
+	.driver = {
+		.name = "iio_sd_adc_mod",
+		.of_match_table = of_match_ptr(sd_adc_of_match),
+	},
+	.probe = iio_sd_mod_probe,
+};
+
+module_platform_driver(iio_sd_mod_adc);
+
+MODULE_DESCRIPTION("Basic sigma delta modulator");
+MODULE_AUTHOR("Arnaud Pouliquen <[e-mail]>");
+MODULE_LICENSE("GPL v2");