diff --git a/MAINTAINERS b/MAINTAINERS
index ae09eb4f4a760f983e51a48702f46823da4dc21b..6f0ff7269f155ac0ef67afc87536df08288e4cf3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -809,11 +809,11 @@ L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
 S:	Maintained
 F:	sound/aoa/
 
-APEX EMBEDDED SYSTEMS STX104 DAC DRIVER
+APEX EMBEDDED SYSTEMS STX104 IIO DRIVER
 M:	William Breathitt Gray <vilhelm.gray@gmail.com>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
-F:	drivers/iio/dac/stx104.c
+F:	drivers/iio/adc/stx104.c
 
 APM DRIVER
 M:	Jiri Kosina <jikos@kernel.org>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 9f8e3813930ebb8556ee61a53010c967195cf236..ee7ab81e4cef91ab889db4d907db8d4851b30b90 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -418,6 +418,21 @@ config ROCKCHIP_SARADC
 	  To compile this driver as a module, choose M here: the
 	  module will be called rockchip_saradc.
 
+config STX104
+	tristate "Apex Embedded Systems STX104 driver"
+	depends on X86 && ISA_BUS_API
+	select GPIOLIB
+	help
+	  Say yes here to build support for the Apex Embedded Systems STX104
+	  integrated analog PC/104 card.
+
+	  This driver supports the 16 channels of single-ended (8 channels of
+	  differential) analog inputs, 2 channels of analog output, 4 digital
+	  inputs, and 4 digital outputs provided by the STX104.
+
+	  The base port addresses for the devices may be configured via the base
+	  array module parameter.
+
 config TI_ADC081C
 	tristate "Texas Instruments ADC081C/ADC101C/ADC121C family"
 	depends on I2C
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index d1a20b658c9a936fb6f5c9b4b4dded44b5786433..7a40c04c311f9c43f6e17288a67851ef6739ce70 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_PALMAS_GPADC) += palmas_gpadc.o
 obj-$(CONFIG_QCOM_SPMI_IADC) += qcom-spmi-iadc.o
 obj-$(CONFIG_QCOM_SPMI_VADC) += qcom-spmi-vadc.o
 obj-$(CONFIG_ROCKCHIP_SARADC) += rockchip_saradc.o
+obj-$(CONFIG_STX104) += stx104.o
 obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
 obj-$(CONFIG_TI_ADC0832) += ti-adc0832.o
 obj-$(CONFIG_TI_ADC12138) += ti-adc12138.o
diff --git a/drivers/iio/dac/stx104.c b/drivers/iio/adc/stx104.c
similarity index 60%
rename from drivers/iio/dac/stx104.c
rename to drivers/iio/adc/stx104.c
index 792a97164cb28e04dd25d44cdffd8541b05f19c4..7ca12d58e75085982f8518363bbdb1dae325aefa 100644
--- a/drivers/iio/dac/stx104.c
+++ b/drivers/iio/adc/stx104.c
@@ -1,5 +1,5 @@
 /*
- * DAC driver for the Apex Embedded Systems STX104
+ * IIO driver for the Apex Embedded Systems STX104
  * Copyright (C) 2016 William Breathitt Gray
  *
  * This program is free software; you can redistribute it and/or modify
@@ -20,19 +20,30 @@
 #include <linux/io.h>
 #include <linux/ioport.h>
 #include <linux/isa.h>
+#include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/spinlock.h>
 
-#define STX104_NUM_CHAN 2
-
-#define STX104_CHAN(chan) {				\
+#define STX104_OUT_CHAN(chan) {				\
 	.type = IIO_VOLTAGE,				\
 	.channel = chan,				\
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),	\
 	.indexed = 1,					\
 	.output = 1					\
 }
+#define STX104_IN_CHAN(chan, diff) {					\
+	.type = IIO_VOLTAGE,						\
+	.channel = chan,						\
+	.channel2 = chan,						\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_HARDWAREGAIN) |	\
+		BIT(IIO_CHAN_INFO_OFFSET) | BIT(IIO_CHAN_INFO_SCALE),	\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),			\
+	.indexed = 1,							\
+	.differential = diff						\
+}
+
+#define STX104_NUM_OUT_CHAN 2
 
 #define STX104_EXTENT 16
 
@@ -47,8 +58,8 @@ MODULE_PARM_DESC(base, "Apex Embedded Systems STX104 base addresses");
  * @base:		base port address of the IIO device
  */
 struct stx104_iio {
-	unsigned chan_out_states[STX104_NUM_CHAN];
-	unsigned base;
+	unsigned int chan_out_states[STX104_NUM_OUT_CHAN];
+	unsigned int base;
 };
 
 /**
@@ -69,28 +80,95 @@ static int stx104_read_raw(struct iio_dev *indio_dev,
 	struct iio_chan_spec const *chan, int *val, int *val2, long mask)
 {
 	struct stx104_iio *const priv = iio_priv(indio_dev);
+	unsigned int adc_config;
+	int adbu;
+	int gain;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		/* get gain configuration */
+		adc_config = inb(priv->base + 11);
+		gain = adc_config & 0x3;
+
+		*val = 1 << gain;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_RAW:
+		if (chan->output) {
+			*val = priv->chan_out_states[chan->channel];
+			return IIO_VAL_INT;
+		}
+
+		/* select ADC channel */
+		outb(chan->channel | (chan->channel << 4), priv->base + 2);
+
+		/* trigger ADC sample capture and wait for completion */
+		outb(0, priv->base);
+		while (inb(priv->base + 8) & BIT(7));
+
+		*val = inw(priv->base);
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_OFFSET:
+		/* get ADC bipolar/unipolar configuration */
+		adc_config = inb(priv->base + 11);
+		adbu = !(adc_config & BIT(2));
+
+		*val = -32768 * adbu;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		/* get ADC bipolar/unipolar and gain configuration */
+		adc_config = inb(priv->base + 11);
+		adbu = !(adc_config & BIT(2));
+		gain = adc_config & 0x3;
+
+		*val = 5;
+		*val2 = 15 - adbu + gain;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	}
 
-	if (mask != IIO_CHAN_INFO_RAW)
-		return -EINVAL;
-
-	*val = priv->chan_out_states[chan->channel];
-
-	return IIO_VAL_INT;
+	return -EINVAL;
 }
 
 static int stx104_write_raw(struct iio_dev *indio_dev,
 	struct iio_chan_spec const *chan, int val, int val2, long mask)
 {
 	struct stx104_iio *const priv = iio_priv(indio_dev);
-	const unsigned chan_addr_offset = 2 * chan->channel;
 
-	if (mask != IIO_CHAN_INFO_RAW)
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		/* Only four gain states (x1, x2, x4, x8) */
+		switch (val) {
+		case 1:
+			outb(0, priv->base + 11);
+			break;
+		case 2:
+			outb(1, priv->base + 11);
+			break;
+		case 4:
+			outb(2, priv->base + 11);
+			break;
+		case 8:
+			outb(3, priv->base + 11);
+			break;
+		default:
+			return -EINVAL;
+		}
+
+		return 0;
+	case IIO_CHAN_INFO_RAW:
+		if (chan->output) {
+			/* DAC can only accept up to a 16-bit value */
+			if ((unsigned int)val > 65535)
+				return -EINVAL;
+
+			priv->chan_out_states[chan->channel] = val;
+			outw(val, priv->base + 4 + 2 * chan->channel);
+
+			return 0;
+		}
 		return -EINVAL;
+	}
 
-	priv->chan_out_states[chan->channel] = val;
-	outw(val, priv->base + 4 + chan_addr_offset);
-
-	return 0;
+	return -EINVAL;
 }
 
 static const struct iio_info stx104_info = {
@@ -99,9 +177,22 @@ static const struct iio_info stx104_info = {
 	.write_raw = stx104_write_raw
 };
 
-static const struct iio_chan_spec stx104_channels[STX104_NUM_CHAN] = {
-	STX104_CHAN(0),
-	STX104_CHAN(1)
+/* single-ended input channels configuration */
+static const struct iio_chan_spec stx104_channels_sing[] = {
+	STX104_OUT_CHAN(0), STX104_OUT_CHAN(1),
+	STX104_IN_CHAN(0, 0), STX104_IN_CHAN(1, 0), STX104_IN_CHAN(2, 0),
+	STX104_IN_CHAN(3, 0), STX104_IN_CHAN(4, 0), STX104_IN_CHAN(5, 0),
+	STX104_IN_CHAN(6, 0), STX104_IN_CHAN(7, 0), STX104_IN_CHAN(8, 0),
+	STX104_IN_CHAN(9, 0), STX104_IN_CHAN(10, 0), STX104_IN_CHAN(11, 0),
+	STX104_IN_CHAN(12, 0), STX104_IN_CHAN(13, 0), STX104_IN_CHAN(14, 0),
+	STX104_IN_CHAN(15, 0)
+};
+/* differential input channels configuration */
+static const struct iio_chan_spec stx104_channels_diff[] = {
+	STX104_OUT_CHAN(0), STX104_OUT_CHAN(1),
+	STX104_IN_CHAN(0, 1), STX104_IN_CHAN(1, 1), STX104_IN_CHAN(2, 1),
+	STX104_IN_CHAN(3, 1), STX104_IN_CHAN(4, 1), STX104_IN_CHAN(5, 1),
+	STX104_IN_CHAN(6, 1), STX104_IN_CHAN(7, 1)
 };
 
 static int stx104_gpio_get_direction(struct gpio_chip *chip,
@@ -188,13 +279,27 @@ static int stx104_probe(struct device *dev, unsigned int id)
 
 	indio_dev->info = &stx104_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->channels = stx104_channels;
-	indio_dev->num_channels = STX104_NUM_CHAN;
+
+	/* determine if differential inputs */
+	if (inb(base[id] + 8) & BIT(5)) {
+		indio_dev->num_channels = ARRAY_SIZE(stx104_channels_diff);
+		indio_dev->channels = stx104_channels_diff;
+	} else {
+		indio_dev->num_channels = ARRAY_SIZE(stx104_channels_sing);
+		indio_dev->channels = stx104_channels_sing;
+	}
+
 	indio_dev->name = dev_name(dev);
 
 	priv = iio_priv(indio_dev);
 	priv->base = base[id];
 
+	/* configure device for software trigger operation */
+	outb(0, base[id] + 9);
+
+	/* initialize gain setting to x1 */
+	outb(0, base[id] + 11);
+
 	/* initialize DAC output to 0V */
 	outw(0, base[id] + 4);
 	outw(0, base[id] + 6);
@@ -251,5 +356,5 @@ static struct isa_driver stx104_driver = {
 module_isa_driver(stx104_driver, num_stx104);
 
 MODULE_AUTHOR("William Breathitt Gray <vilhelm.gray@gmail.com>");
-MODULE_DESCRIPTION("Apex Embedded Systems STX104 DAC driver");
+MODULE_DESCRIPTION("Apex Embedded Systems STX104 IIO driver");
 MODULE_LICENSE("GPL v2");
diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
index e8656ba9bbb81a273ee3f89813f06d48bf63f78d..120b2447846978192d71f2aeb334e48b81ed157f 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -264,16 +264,6 @@ config MCP4922
 	  To compile this driver as a module, choose M here: the module
 	  will be called mcp4922.
 
-config STX104
-	tristate "Apex Embedded Systems STX104 DAC driver"
-	depends on X86 && ISA_BUS_API
-	select GPIOLIB
-	help
-	  Say yes here to build support for the 2-channel DAC and GPIO on the
-	  Apex Embedded Systems STX104 integrated analog PC/104 card. The base
-	  port addresses for the devices may be configured via the base array
-	  module parameter.
-
 config VF610_DAC
 	tristate "Vybrid vf610 DAC driver"
 	depends on OF
diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
index c50dbe082a708a08a134bb5146c4a66d44157b05..27642bbf75f22ce93fe1471cdf870ee0ed59a1bb 100644
--- a/drivers/iio/dac/Makefile
+++ b/drivers/iio/dac/Makefile
@@ -28,5 +28,4 @@ obj-$(CONFIG_MAX517) += max517.o
 obj-$(CONFIG_MAX5821) += max5821.o
 obj-$(CONFIG_MCP4725) += mcp4725.o
 obj-$(CONFIG_MCP4922) += mcp4922.o
-obj-$(CONFIG_STX104) += stx104.o
 obj-$(CONFIG_VF610_DAC) += vf610_dac.o