iio: Introduce the generic counter interface

This patch introduces the dummy counter driver. The dummy counter driver serves as a reference implementation of a driver that utilizes the Generic Counter interface.

Writing individual '1' and '0' characters to the Signal attributes allows a user to simulate a typical Counter Signal input stream for evaluation; the Counter will evaluate the Signal data based on the respective trigger mode for the associated Signal, and trigger the associated counter function specified by the respective function mode. The current Value value may be read, and the Value value preset by a write.

Signed-off-by William Breathitt Gray <[email protected]>

---
 drivers/iio/counter/Kconfig         |  15 ++
 drivers/iio/counter/Makefile        |   1 +
 drivers/iio/counter/dummy-counter.c | 293 ++++++++++++++++++++++++++++++++++++
 3 files changed, 309 insertions(+)
 create mode 100644 drivers/iio/counter/dummy-counter.c

drivers/iio/counter/Kconfig +15 -0

index c8becfe78e28..494aed40e9c9 100644
@@ -22,6 +22,21 @@ config 104_QUAD_8
 	  The base port addresses for the devices may be configured via the base
 	  array module parameter.
 
+config DUMMY_COUNTER
+	tristate "Dummy counter driver"
+	help
+	  Select this option to enable the dummy counter driver. The dummy
+	  counter driver serves as a reference implementation of a driver that
+	  utilizes the Generic Counter interface.
+
+	  Writing individual '1' and '0' characters to the Signal attributes
+	  allows a user to simulate a typical Counter Signal input stream for
+	  evaluation; the Counter will evaluate the Signal data based on the
+	  respective trigger mode for the associated Signal, and trigger the
+	  associated counter function specified by the respective function mode.
+	  The current Value value may be read, and the Value value preset by a
+	  write.
+
 config STM32_LPTIMER_CNT
 	tristate "STM32 LP Timer encoder counter driver"
 	depends on MFD_STM32_LPTIMER || COMPILE_TEST

drivers/iio/counter/Makefile +1 -0

index 1b9a896eb488..8c2ef0115426 100644
@@ -5,4 +5,5 @@
 # When adding new entries keep the list in alphabetical order
 
 obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
+obj-$(CONFIG_DUMMY_COUNTER)	+= dummy-counter.o
 obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o

drivers/iio/counter/dummy-counter.c new file +36 -0

new file mode 100644
index 000000000000..6ecc9854894f
@@ -0,0 +1,293 @@
+/*
+ * Dummy counter driver
+ * Copyright (C) 2017 William Breathitt Gray
+ *
+ * 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.
+ *
+ * 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/device.h>
+#include <linux/errno.h>
+#include <linux/iio/counter.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#define DUMCNT_NUM_COUNTERS 2
+/**
+ * struct dumcnt - private data structure
+ * @counter:	instance of the iio_counter
+ * @counts:	array of accumulation values
+ * @states:	array of input line states
+ */
+struct dumcnt {
+	struct iio_counter counter;
+	unsigned int counts[DUMCNT_NUM_COUNTERS];
+	unsigned int states[DUMCNT_NUM_COUNTERS];
+};
+
+static int dumcnt_signal_read(struct iio_counter *counter,
+	struct iio_counter_signal *signal, int *val, int *val2)

drivers/iio/counter/dummy-counter.c new file +92 -0

+	struct dumcnt *const priv = counter->driver_data;
+	const unsigned int id = signal->id;
+	const unsigned int prev_state = priv->states[id];
+	struct iio_counter_value *const value = counter->values + id;
+	const unsigned int function_mode = value->mode;
+	const unsigned int trigger_mode = value->triggers[0].mode;
+	unsigned int triggered = 0;
+
+	if (val && val != 1)
+		return -EINVAL;
+
+	/* If no state change then just exit */
+	if (prev_state == val)
+		return 0;
+
+	priv->states[id] = val;
+
+	switch (trigger_mode) {
+	/* "none" case */
+	case 0:
+		return 0;
+	/* "rising edge" case */
+	case 1:
+		if (!prev_state)
+			triggered = 1;
+		break;
+	/* "falling edge" case */
+	case 2:
+		if (prev_state)
+			triggered = 1;
+		break;
+	/* "both edges" case */
+	case 3:
+		triggered = 1;
+		break;
+	}
+
+	/* If counter function triggered */
+	if (triggered)
+		/* "increase" case */
+		if (function_mode)
+			priv->counts[id]++;
+		/* "decrease" case */
+		else
+			priv->counts[id]--;
+
+	return 0;
+}
+
+static int dumcnt_trigger_mode_set(struct iio_counter *counter,
+	struct iio_counter_value *value, struct iio_counter_trigger *trigger,
+	unsigned int mode)
+{
+	if (mode >= trigger->num_trigger_modes)
+		return -EINVAL;
+
+	trigger->mode = mode;
+
+	return 0;
+}
+
+static int dumcnt_trigger_mode_get(struct iio_counter *counter,
+	struct iio_counter_value *value, struct iio_counter_trigger *trigger)
+{
+	return trigger->mode;
+}
+
+static int dumcnt_value_read(struct iio_counter *counter,
+	struct iio_counter_value *value, int *val, int *val2)
+{
+	struct dumcnt *const priv = counter->driver_data;
+
+	*val = priv->counts[value->id];
+
+	return IIO_VAL_INT;
+}
+
+static int dumcnt_value_write(struct iio_counter *counter,
+	struct iio_counter_value *value, int val, int val2)
+{
+	struct dumcnt *const priv = counter->driver_data;
+
+	priv->counts[value->id] = val;
+
+	return 0;
+}
+
+static int dumcnt_value_function_set(struct iio_counter *counter,
+	struct iio_counter_value *value, unsigned int mode)
+{
+	if (mode >= value->num_function_modes)
+		return -EINVAL;

drivers/iio/counter/dummy-counter.c new file +5 -0

+}
+
+static const struct iio_counter_ops dumcnt_ops = {
+	.signal_read = dumcnt_signal_read,
+	.signal_write = dumcnt_signal_write,

drivers/iio/counter/dummy-counter.c new file +15 -0

+	"increase"
+};
+
+#define DUMCNT_SIGNAL(_id, _name) {	\
+	.id = _id,			\
+	.name = _name			\
+}
+
+static const struct iio_counter_signal dumcnt_signals[] = {
+	DUMCNT_SIGNAL(0, "Signal A"), DUMCNT_SIGNAL(1, "Signal B")
+};
+
+#define DUMCNT_VALUE(_id, _name) {					\
+	.id = _id,							\
+	.name = _name,							\

drivers/iio/counter/dummy-counter.c new file +15 -0

+		triggers->trigger_modes = dumcnt_trigger_modes;
+		triggers->num_trigger_modes = ARRAY_SIZE(dumcnt_trigger_modes);
+		triggers->signal = &signals[i];
+
+		values[i].triggers = triggers;
+		values[i].num_triggers = 1;
+	}
+
+	dumcnt = devm_kzalloc(dev, sizeof(*dumcnt), GFP_KERNEL);
+	if (!dumcnt)
+		return -ENOMEM;
+
+	dumcnt->counter.name = dev_name(dev);
+	dumcnt->counter.dev = dev;
+	dumcnt->counter.ops = &dumcnt_ops;

drivers/iio/counter/dummy-counter.c new file +27 -0

+	dumcnt_device = platform_device_alloc(dumcnt_driver.driver.name, -1);
+	if (!dumcnt_device)
+		return -ENOMEM;
+
+	err = platform_device_add(dumcnt_device);
+	if (err)
+		goto err_platform_device;
+
+	err = platform_driver_probe(&dumcnt_driver, dumcnt_probe);
+	if (err)
+		goto err_platform_driver;
+
+	return 0;
+
+err_platform_driver:
+	platform_device_del(dumcnt_device);
+err_platform_device:
+	platform_device_put(dumcnt_device);
+	return err;
+}
+
+module_init(dumcnt_init);
+module_exit(dumcnt_exit);
+
+MODULE_AUTHOR("William Breathitt Gray <[email protected]>");
+MODULE_DESCRIPTION("Dummy counter driver");
+MODULE_LICENSE("GPL v2");

This patch adds support for the IIO generic counter interface to the 104-QUAD-8 driver. The existing 104-QUAD-8 device interface should not be affected by this patch; all changes are intended as supplemental additions as perceived by the user.

IIO Counter Signals are defined for all quadrature input pairs (A and B), as well as index input lines. However, IIO Counter Triggers are not created for the index input Signals. IIO Counter Values are created for the eight quadrature channel counts, and their respective Signals are associated via IIO Counter Triggers.

The new generic counter interface sysfs attributes expose the same functionality and data available via the existing 104-QUAD-8 device interface. Four IIO Counter Value function modes are available, correlating to the four possible quadrature mode configurations:
"non-quadrature," "quadrature x1," "quadrature x2," and "quadrature x4."

Signed-off-by William Breathitt Gray <[email protected]>

---
 drivers/iio/counter/104-quad-8.c | 294 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 277 insertions(+), 17 deletions(-)

drivers/iio/counter/104-quad-8.c +230 -14

index b56985078d8c..690a520e70df 100644
@@ -16,6 +16,7 @@
 #include <linux/bitops.h>
 #include <linux/device.h>
 #include <linux/errno.h>
+#include <linux/iio/counter.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/types.h>
 #include <linux/io.h>

@@ -24,6 +25,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
+#include <linux/string.h>
 #include <linux/types.h>
 
 #define QUAD8_EXTENT 32

@@ -37,6 +39,7 @@ MODULE_PARM_DESC(base, "ACCES 104-QUAD-8 base addresses");
 
 /**
  * struct quad8_iio - IIO device private data structure
+ * @counter:		instance of the iio_counter
  * @preset:		array of preset values
  * @count_mode:		array of count mode configurations
  * @quadrature_mode:	array of quadrature mode configurations

@@ -48,6 +51,7 @@ MODULE_PARM_DESC(base, "ACCES 104-QUAD-8 base addresses");
  * @base:		base port address of the IIO device
  */
 struct quad8_iio {
+	struct iio_counter counter;
 	unsigned int preset[QUAD8_NUM_COUNTERS];
 	unsigned int count_mode[QUAD8_NUM_COUNTERS];
 	unsigned int quadrature_mode[QUAD8_NUM_COUNTERS];

@@ -527,33 +531,289 @@ static const struct iio_chan_spec quad8_channels[] = {
 	QUAD8_COUNT_CHAN(7), QUAD8_INDEX_CHAN(7)
 };
 
+static int quad8_signal_read(struct iio_counter *counter,
+	struct iio_counter_signal *signal, int *val, int *val2)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+
+	if (signal->id < 16)
+		return -EINVAL;
+
+	*val = !!(inb(priv->base + 0x16) & BIT(signal->id - 16));
+
+	return IIO_VAL_INT;
+}
+
+static int quad8_trigger_mode_get(struct iio_counter *counter,
+	struct iio_counter_value *value, struct iio_counter_trigger *trigger)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+	const unsigned int mode = priv->quadrature_mode[value->id];
+	const unsigned int scale = priv->quadrature_scale[value->id];
+	unsigned int direction;
+	const unsigned int flag_addr = priv->base + 2 * value->id + 1;
+	const int signal_id = trigger->signal->id % 2;
+
+	if (mode)
+		switch (scale) {
+		case 0:
+			/* U/D flag: 1 = up, 0 = down */
+			/* direction: 0 = up, 1 = down */
+			direction = !(inb(flag_addr) & BIT(5));
+			if (!signal_id)
+				return direction + 1;
+			break;
+		case 1:
+			if (!signal_id)
+				return 3;
+			break;
+		case 2:
+			return 3;
+		}
+	else
+		if (!signal_id)
+			return 1;
+
+	return 0;
+}
+
+static int quad8_value_read(struct iio_counter *counter,
+	struct iio_counter_value *value, int *val, int *val2)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+	const int base_offset = priv->base + 2 * value->id;
+	unsigned int flags;
+	unsigned int borrow;
+	unsigned int carry;
+	int i;
+
+	flags = inb(base_offset + 1);
+	borrow = flags & BIT(0);
+	carry = !!(flags & BIT(1));
+
+	/* Borrow XOR Carry effectively doubles count range */
+	*val = (borrow ^ carry) << 24;
+
+	/* Reset Byte Pointer; transfer Counter to Output Latch */
+	outb(0x11, base_offset + 1);
+
+	for (i = 0; i < 3; i++)
+		*val |= (unsigned int)inb(base_offset) << (8 * i);
+
+	return IIO_VAL_INT;
+}
+
+static int quad8_value_write(struct iio_counter *counter,
+	struct iio_counter_value *value, int val, int val2)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+	const int base_offset = priv->base + 2 * value->id;
+	int i;
+
+	/* Only 24-bit values are supported */
+	if ((unsigned int)val > 0xFFFFFF)
+		return -EINVAL;
+
+	/* Reset Byte Pointer */
+	outb(0x01, base_offset + 1);
+
+	/* Counter can only be set via Preset Register */
+	for (i = 0; i < 3; i++)
+		outb(val >> (8 * i), base_offset);
+
+	/* Transfer Preset Register to Counter */
+	outb(0x08, base_offset + 1);
+
+	/* Reset Byte Pointer */
+	outb(0x01, base_offset + 1);
+
+	/* Set Preset Register back to original value */
+	val = priv->preset[value->id];
+	for (i = 0; i < 3; i++)
+		outb(val >> (8 * i), base_offset);
+
+	/* Reset Borrow, Carry, Compare, and Sign flags */
+	outb(0x02, base_offset + 1);
+	/* Reset Error flag */
+	outb(0x06, base_offset + 1);
+
+	return 0;
+}
+
+static int quad8_value_function_set(struct iio_counter *counter,
+	struct iio_counter_value *value, unsigned int mode)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+	const unsigned int mode_cfg = mode << 3 |
+		priv->count_mode[value->id] << 1;
+	const unsigned int idr_cfg = priv->index_polarity[value->id] << 1;
+	const int base_offset = priv->base + 2 * value->id + 1;
+
+	if (mode)
+		priv->quadrature_scale[value->id] = mode - 1;
+	else {
+		/* Quadrature scaling only available in quadrature mode */
+		priv->quadrature_scale[value->id] = 0;
+
+		/* Synchronous function not supported in non-quadrature mode */
+		if (priv->synchronous_mode[value->id]) {
+			priv->synchronous_mode[value->id] = 0;
+			outb(0x60 | idr_cfg, base_offset);
+		}
+	}
+
+	priv->quadrature_mode[value->id] = !!mode;
+
+	/* Load mode configuration to Counter Mode Register */
+	outb(0x20 | mode_cfg, base_offset);
+
+	return 0;
+}
+
+static int quad8_value_function_get(struct iio_counter *counter,
+	struct iio_counter_value *value)
+{
+	struct quad8_iio *const priv = counter->driver_data;
+	unsigned int quadrature_mode = priv->quadrature_mode[value->id];
+
+	return (quadrature_mode) ? priv->quadrature_scale[value->id] + 1 : 0;
+}
+
+static const struct iio_counter_ops quad8_ops = {
+	.signal_read = quad8_signal_read,
+	.trigger_mode_get = quad8_trigger_mode_get,
+	.value_read = quad8_value_read,
+	.value_write = quad8_value_write,
+	.value_function_set = quad8_value_function_set,
+	.value_function_get = quad8_value_function_get
+};
+
+static const char *const quad8_function_modes[] = {
+	"non-quadrature",
+	"quadrature x1",
+	"quadrature x2",
+	"quadrature x4"
+};
+
+#define QUAD8_SIGNAL(_id, _name) {	\
+	.id = _id,			\
+	.name = _name			\
+}
+
+static const struct iio_counter_signal quad8_signals[] = {
+	QUAD8_SIGNAL(0, "Channel 1 Quadrature A"),
+	QUAD8_SIGNAL(1, "Channel 1 Quadrature B"),
+	QUAD8_SIGNAL(2, "Channel 2 Quadrature A"),
+	QUAD8_SIGNAL(3, "Channel 2 Quadrature B"),
+	QUAD8_SIGNAL(4, "Channel 3 Quadrature A"),
+	QUAD8_SIGNAL(5, "Channel 3 Quadrature B"),
+	QUAD8_SIGNAL(6, "Channel 4 Quadrature A"),
+	QUAD8_SIGNAL(7, "Channel 4 Quadrature B"),
+	QUAD8_SIGNAL(8, "Channel 5 Quadrature A"),
+	QUAD8_SIGNAL(9, "Channel 5 Quadrature B"),
+	QUAD8_SIGNAL(10, "Channel 6 Quadrature A"),
+	QUAD8_SIGNAL(11, "Channel 6 Quadrature B"),
+	QUAD8_SIGNAL(12, "Channel 7 Quadrature A"),
+	QUAD8_SIGNAL(13, "Channel 7 Quadrature B"),
+	QUAD8_SIGNAL(14, "Channel 8 Quadrature A"),
+	QUAD8_SIGNAL(15, "Channel 8 Quadrature B"),
+	QUAD8_SIGNAL(16, "Channel 1 Index"),
+	QUAD8_SIGNAL(17, "Channel 2 Index"),
+	QUAD8_SIGNAL(18, "Channel 3 Index"),
+	QUAD8_SIGNAL(19, "Channel 4 Index"),
+	QUAD8_SIGNAL(20, "Channel 5 Index"),
+	QUAD8_SIGNAL(21, "Channel 6 Index"),
+	QUAD8_SIGNAL(22, "Channel 7 Index"),
+	QUAD8_SIGNAL(23, "Channel 8 Index")
+};
+
+#define QUAD8_VALUE(_id, _name) {					\
+	.id = _id,							\
+	.name = _name,							\
+	.mode = 0,							\
+	.function_modes = quad8_function_modes,				\
+	.num_function_modes = ARRAY_SIZE(quad8_function_modes)		\
+}
+
+static const struct iio_counter_value quad8_values[] = {
+	QUAD8_VALUE(0, "Channel 1 Count"), QUAD8_VALUE(1, "Channel 2 Count"),
+	QUAD8_VALUE(2, "Channel 3 Count"), QUAD8_VALUE(3, "Channel 4 Count"),
+	QUAD8_VALUE(4, "Channel 5 Count"), QUAD8_VALUE(5, "Channel 6 Count"),
+	QUAD8_VALUE(6, "Channel 7 Count"), QUAD8_VALUE(7, "Channel 8 Count")
+};
+
+static const char *const quad8_trigger_modes[] = {
+	"none",
+	"rising edge",
+	"falling edge",
+	"both edges"
+};
+
 static int quad8_probe(struct device *dev, unsigned int id)
 {
-	struct iio_dev *indio_dev;
-	struct quad8_iio *priv;
+	struct iio_counter_signal *signals;
+	const size_t num_signals = ARRAY_SIZE(quad8_signals);
+	struct iio_counter_value *values;
+	const size_t num_values = ARRAY_SIZE(quad8_values);
+	struct iio_counter_trigger *triggers;
+	struct quad8_iio *quad8iio;
 	int i, j;
 	unsigned int base_offset;
 
-	indio_dev = devm_iio_device_alloc(dev, sizeof(*priv));
-	if (!indio_dev)
-		return -ENOMEM;
-
-	if (!devm_request_region(dev, base[id], QUAD8_EXTENT,
-		dev_name(dev))) {
+	if (!devm_request_region(dev, base[id], QUAD8_EXTENT, dev_name(dev))) {
 		dev_err(dev, "Unable to lock port addresses (0x%X-0x%X)\n",
 			base[id], base[id] + QUAD8_EXTENT);
 		return -EBUSY;
 	}
 
-	indio_dev->info = &quad8_info;
-	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->num_channels = ARRAY_SIZE(quad8_channels);
-	indio_dev->channels = quad8_channels;
-	indio_dev->name = dev_name(dev);
-	indio_dev->dev.parent = dev;
+	signals = devm_kmalloc(dev, sizeof(quad8_signals), GFP_KERNEL);

drivers/iio/counter/104-quad-8.c +28 -3

+		triggers[0].trigger_modes = quad8_trigger_modes;
+		triggers[0].num_trigger_modes = ARRAY_SIZE(quad8_trigger_modes);
+		triggers[0].signal = &signals[2 * i];
+		triggers[1].mode = 0;
+		triggers[1].trigger_modes = quad8_trigger_modes;
+		triggers[1].num_trigger_modes = ARRAY_SIZE(quad8_trigger_modes);
+		triggers[1].signal = &signals[2 * i + 1];
+
+		values[i].triggers = triggers;
+		values[i].num_triggers = 2;
+	}
+
+	quad8iio = devm_kzalloc(dev, sizeof(*quad8iio), GFP_KERNEL);
+	if (!quad8iio)
+		return -ENOMEM;
 
-	priv = iio_priv(indio_dev);
-	priv->base = base[id];
+	quad8iio->counter.name = dev_name(dev);
+	quad8iio->counter.dev = dev;
+	quad8iio->counter.ops = &quad8_ops;
+	quad8iio->counter.signals = signals;
+	quad8iio->counter.num_signals = num_signals;
+	quad8iio->counter.values = values;
+	quad8iio->counter.num_values = num_values;
+	quad8iio->counter.channels = quad8_channels;
+	quad8iio->counter.num_channels = ARRAY_SIZE(quad8_channels);
+	quad8iio->counter.info = &quad8_info;
+	quad8iio->counter.driver_data = quad8iio;
+	quad8iio->base = base[id];
 
 	/* Reset all counters and disable interrupt function */
 	outb(0x01, base[id] + 0x11);

@@ -579,7 +839,7 @@ static int quad8_probe(struct device *dev, unsigned int id)
 	/* Enable all counters */
 	outb(0x00, base[id] + 0x11);
 
-	return devm_iio_device_register(dev, indio_dev);
+	return devm_iio_counter_register(dev, &quad8iio->counter);
 }
 
 static struct isa_driver quad8_driver = {

There have been some significant implementation changes for this version of the patchset. Here's a brief summary of the updates:

- Inline comments throughout the industrial-counter.c file; this should help clarify some of the code and aid in the review of the system architecture

- Simplification of the driver API; primarily, dynamic updates to the Counter Values, Triggers, and Signals lists are no longer allowed -- all relationships must be defined before the Counter is registered to the system

- Dynamic component registration functions (iio_counter_value_register, et al.) have been removed, and now the signals, values, and triggers array members serve to register the components; signals, values, and triggers were previously named init_signals, init_values, and init_triggers respectively -- the "init_" prefix was removed now that dynamic registration is no longer allowed

- Requiring static component relationships means linked lists are no longer necessary so all the list related code has been removed; Signals, Triggers, and Values are now accessed directly from the arrays supplied in the iio_counter structure

- No dynamic additions/substraction of components eliminates the need for mutex locks, so those have been removed as well

- Previously, the entire iio_counter structure was copied and stored as the iio_dev private data; now, only a pointer to the supplied iio_counter structure is stored

- devm_iio_counter_register and devm_iio_counter_unregister functions were incorporated from Benjamin Gaignard's suggestions

- Dummy counter driver provided as a reference for a simple counter implementation utilizing the Generic Counter interface

In a previous discussion, Benjamin noted some conflicts between the Generic Counter and the underlying IIO core code: mapping does not always work out seemlessly and sometimes the IIO core functionality exposure provided via iio_counter is not quite flexible enough. I intend to address these shortcomings in the next version of this patchset hopefully.

In particular, I'm leaning towards separating the Generic Counter interface from the IIO core dependency entirely. Since the Generic Counter inteface focuses on a more abstract representation of a counter device, I don't think it provides a suitable interface to map onto IIO core, which appears to focus more on a representation of the physical hardware itself.

Separating Generic Counter from IIO core should allow a driver to use the IIO core functions (iio_device_register, et al.) to represent the physical nature of their hardware (voltages, currents, etc.), while also utilize the Generic Counter interface to represent the abstract relationships between those Signals and their ultimate counter Values.

In particular, I'm hoping for the Generic Counter system implementation itself to not require all this hoop-jumping (mapping to IIO core functions, jumping back to the parent iio_counter, handling non-matching parameter lists between iio_counter and iio_dev, etc.); that should make the code simpler to debug, more efficient, and more stable in the long-run. I will consider these advantages and disadvantages before committing to a separation however.

Regarding this version of the patchset in particular, I decided to remove the dynamic component registration functionality since I doubt that many devices would require such; almost all, if not all, hardware counters I encountered have static relationships between input lines and the count value (i.e. specific input lines correlate to specific count registers).

The requirement that Counter component relationships are static has opened the possibility of some optimizations in the Generic Counter interface code:

- Signals, Triggers, and Values are provided as arrays; these arrays could benefit from some amount of sorting based on component IDs

- Searching for a component can be more efficient in a sorted array; currently, the code just walks down the array elements and compare the IDs

- Similar to general searching, the arrays are initially verified to gurantee unique IDs; currently, the code walks down the array elements and compares the current element ID with all the elements before and after -- this could be made more efficient with some sorting

There are likely other areas of improvement, so let me know and I'll see what I can do.

William Breathitt Gray (6):
iio: Implement counter channel specification and IIO_SIGNAL constant
iio: Introduce the generic counter interface
iio: Documentation: Add IIO Generic Counter sysfs documentation
docs: Add IIO Generic Counter Interface documentation
iio: Add dummy counter driver
iio: 104-quad-8: Add IIO generic counter interface support

 .../testing/sysfs-bus-iio-generic-counter-sysfs    |  63 ++
 Documentation/driver-api/iio/generic-counter.txt   | 526 ++++++++++++
 MAINTAINERS                                        |   7 +
 drivers/iio/Kconfig                                |   8 +
 drivers/iio/Makefile                               |   1 +
 drivers/iio/counter/104-quad-8.c                   | 294 ++++++-
 drivers/iio/counter/Kconfig                        |  16 +
 drivers/iio/counter/Makefile                       |   1 +
 drivers/iio/counter/dummy-counter.c                | 293 +++++++
 drivers/iio/industrialio-core.c                    |  14 +-
 drivers/iio/industrialio-counter.c                 | 900 +++++++++++++++++++++
 include/linux/iio/counter.h                        | 166 ++++
 include/linux/iio/iio.h                            |   2 +
 include/uapi/linux/iio/types.h                     |   1 +
 14 files changed, 2274 insertions(+), 18 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-generic-counter-sysfs
 create mode 100644 Documentation/driver-api/iio/generic-counter.txt
 create mode 100644 drivers/iio/counter/dummy-counter.c
 create mode 100644 drivers/iio/industrialio-counter.c
 create mode 100644 include/linux/iio/counter.h

This patch adds high-level documentation about the IIO Generic Counter Interface.

Signed-off-by William Breathitt Gray <[email protected]>

---
 Documentation/driver-api/iio/generic-counter.txt | 526 +++++++++++++++++++++++
 1 file changed, 526 insertions(+)
 create mode 100644 Documentation/driver-api/iio/generic-counter.txt

Documentation/driver-api/iio/generic-counter.txt new file +13 -0

new file mode 100644
index 000000000000..0ce43b71e1c7
@@ -0,0 +1,526 @@
+=========================
+Generic Counter Interface
+=========================
+
+Introduction
+============
+
+Counter devices are prevalent within a diverse spectrum of industries.
+The ubiquitous presence of these devices necessitates a common interface
+and standard of interaction and exposure. This driver API attempts to
+resolve the issue of duplicate code found among existing counter device
+drivers by introducing a generic counter interface for consumption. The
+generic counter interface enables drivers to support and expose a common

Documentation/driver-api/iio/generic-counter.txt new file +10 -0

+
+        Value                Trigger        Signal
+        -----                -------        ------
++---------------------+
+| Data: Count         |    Rising Edge     ________
+| Function: Increment |  <-------------   / Source \
+|                     |                  ____________
++---------------------+
+
+In this example, the Signal is a source input line with a pulsing

For

Documentation/driver-api/iio/generic-counter.txt new file +12 -0

+example, a quadrature encoder counter device can keep track of position
+based on the states of two input lines.
+
+           Value                 Trigger      Signal
+           -----                 -------      ------
++-------------------------+
+| Data: Position          |    Both Edges      ___
+| Function: Quadrature x4 |  <-------------   / A \
+|                         |                  _______
+|                         |
+|                         |    Both Edges      ___
+|                         |  <-------------   / B \

Documentation/driver-api/iio/generic-counter.txt new file +7 -0

+
+Signal associated to the same Value can have differing trigger
+conditions. For example, a quadrature encoder counter device operating
+in a non-quadrature mode could have one input line dedicated for
+movement and a second input line dedicated for direction.
+
+           Value                  Trigger      Signal

Documentation/driver-api/iio/generic-counter.txt new file +50 -0

+
+Although the examples thus far have been representations of physical
+devices, this is not a necessity. A counter simply represent the
+evaluation (Value) of input data (Signals) triggered by specific
+conditions (Triggers). A counter can be the representation of more
+abstract components.
+
+For example, suppose a counter representation is desired for a DNA
+sequence analysizer which detects possible genetic diseases.
+
+        Value                     Trigger           Signal
+        -----                     -------           ------
++---------------------+
+| Data: Diseases      |    Gene Transcript (EST)     _____
+| Function: Cancers   |  <-----------------------   / DNA \ (GAAGTGC...)
+|                     |                            _________
++---------------------+
+
+In this scenario, the Signal is a stream of DNA nucleotide bases (As,
+Ts, Cs, and Gs), the Trigger is expressed sequence tags (ESTs), and the
+Value is a list of diseases discovered (in this case the function is
+evaluating for possible cancers). Note how the Signal in this example
+does not represent a physical voltage line, nor does the Trigger
+represent a physical voltage line state change, nor does the Value
+represent a strictly decimal data value.
+
+The DNA sequence analysizer example is contrived to illustrate the
+flexibility of the generic counter paradigm by demonstrating its
+capability of representing abstract concepts; however, physical devices
+are likely to be more fitting for such a representation.
+
+The key concept is that the Signal, Trigger, and Value are abstract
+representations which do not need to be closely married to their
+respective physical sources. This allows the user of a counter to
+divorce themselves from the nuances of physical components (such as
+whether an input line is differential or single-ended) and focus on the
+core idea of what the data and process represent (an accumulated count
+of rising edges).
+
+Userspace Interface
+===================
+
+Several sysfs attributes are generated by the generic counter interface,
+and reside under the /sys/bus/iio/devices/iio:deviceX directory.
+
+Each counter has a respective set of countX-Y and signalX-Y prefixed
+attributes, where X is the id set in the counter structure, and Y is the
+id of the respective Value or Signal.
+
+The generic counter interface sysfs attributes are as follows:

Documentation/driver-api/iio/generic-counter.txt new file +28 -0

+        signalX-Y_raw: Signal data
+
+Through these sysfs attributes, programs and scripts may interact with
+the generic counter paradigm Values, Triggers, and Signals of respective
+counter devices.
+
+Driver API
+==========
+
+Driver authors may utilize the generic counter interface in their code
+by including the include/linux/iio/counter.h header file. This header
+file provides several core data structures and function prototypes for
+defining a generic counter.
+
+struct iio_counter_signal
+-------------------------
+
+This structure defines a generic counter paradigm Signal component;
+typically this will correlate with an input channel on a physical
+counter device. This structure is the simplest to define with only two
+structure members which require explicit configuration:
+
+        id:     Unique ID used to identify the Signal
+
+        name:   Device-specific Signal name (typically the device input
+                channel name)
+
+struct iio_counter_trigger

Documentation/driver-api/iio/generic-counter.txt new file +23 -0

+
+        num_trigger_modes:      Number of trigger modes provided in
+	                        trigger_modes array
+
+        signal:                 Pointer to associated Signal
+
+struct iio_counter_value
+------------------------
+
+This structure defines a generic counter paradigm Value component;
+typically this will correlate with the read data (the "count" value)
+provided by a physical counter device. This structure requires the
+explicit configuration of an ID, name, function modes (the function
+triggered on a Trigger condition), and optionally a set of initial
+associated Triggers:
+
+        id:                     Unique ID used to identify the Signal
+
+        name:                   Device-specific Value name (typically
+	                        the device read channel name)
+
+        mode:                   Index of the current function mode state
+

Documentation/driver-api/iio/generic-counter.txt new file +9 -0

+
+	signal_write:           Function to write a signal value to the
+	                        device. Parameters are interpreted the
+				same as signal_read.
+
+        trigger_mode_set:       Function to set the trigger mode. mode
+	                        is the index of the requested mode from
+				the value trigger_modes array.
+

Documentation/driver-api/iio/generic-counter.txt new file +70 -0

+
+        value_write:            Function to write a value value to the
+	                        device. Parameters are interpreted the
+				same as value_read.
+
+        value_function_set:     Function to set the value function mode.
+	                        mode is the index of the requested mode
+				from the value function_modes array.
+
+        value_function_get:     Function to get the current value
+	                        function mode. Return value will specify
+				the index of the current mode from the
+				value function_modes array.
+
+struct iio_counter
+------------------
+
+This is the main data structure for a counter device; access to all
+respective Values, Triggers, and Signals is possible from this
+structure. This structure allows the configuration of an ID, name,
+function callbacks, initial Signals and initial Values, auxiliary IIO
+core channels and callbacks, and driver-specific data:
+
+        id:                     Unique ID used to identify the counter
+
+        name:                   Name of the counter device
+
+        dev:                    Device structure, which should be
+				assigned a parent and owner
+
+        ops:                    Function callbacks for counter
+	                        components (Signal, Trigger, Value)
+
+        signals:                Array of Signals
+
+        num_signals:            Number of Signals specified in signals
+	                        array
+
+        values:                 Array of Values
+
+        num_values:             Number of Values specified in values
+	                        array
+
+        channels:               Optional IIO core channels specification
+	                        structure table
+
+        num_channels:           Number of channels specified in channels
+
+        info:                   IIO core function callbacks and constant
+	                        info from driver
+
+        driver_data:            Driver-specific data
+
+Registration functions
+----------------------
+
+Counters may be registered to the system via the iio_counter_register
+function and subsequently unregistered via the iio_counter_unregister
+function. The devm_iio_counter_register and devm_iio_counter_unregister
+functions serve as device memory-managed versions of the
+iio_counter_register and iio_counter_unregister functions.
+
+An initialized iio_counter structure, which defines the Counter, is
+required to be passed in for registration; the Signals, Values, and
+Triggers for the Counter passed in via the signals and values arrays as
+part of the iio_counter structure. If auxiliary IIO core channels and
+functionality are required, IIO core channels and callbacks may be
+passed in via the channels and info members of the passed-in iio_counter
+structure.
+

Documentation/driver-api/iio/generic-counter.txt new file +33 -0

+
+The iio_counter_ops structure serves as a container for driver callbacks
+to communicate with the device; function callbacks are provided to read
+and write various Signals and Values, and set and get the "trigger mode"
+and "function mode" for various Triggers and Values respectively.
+
+To support a counter device, a driver must first allocate the available
+Counter Signals via iio_counter_signal structures. These Signals should
+be stored as an array and set to the signals array member of an
+allocated iio_counter structure before the Counter is registered to the
+system.
+
+Counter Values may be allocated via iio_counter_value structures, and
+respective Counter Signal associations (Triggers) made via
+iio_counter_trigger structures. Associated iio_counter_trigger
+structures are stored as an array and set to the the triggers array
+member of the respective iio_counter_value structure. These
+iio_counter_value structures are set to the values array member of an
+allocated iio_counter structure before the Counter is registered to the
+system.
+
+A counter device is registered to the system by passing the respective
+initialized iio_counter structure to the iio_counter_register function;
+similarly, the iio_counter_unregister function unregisters the
+respective counter.
+
+Architecture
+============
+
+Although the IIO Generic Counter Interface utilizes IIO core under the
+hood, driver authors are not necessarily required to interact with IIO
+core data structures and functions directly -- in theory, such details
+of the system are abstracted away. Driver authors only need to concern

Documentation/driver-api/iio/generic-counter.txt new file +103 -0

+
+This paradigm separation however does result in some mapping concerns
+between Generic Counter functions to IIO core functions; in particular,
+parameters for the IIO core functions expect IIO core data structures
+(e.g. iio_dev and iio_chan_spec) which are not provided directly by the
+parameters for the respective Generic Counter functions. This results in
+a somewhat opaque pathway from a iio_counter structure to its associated
+iio_dev in order to support the required IIO core calls.
+
+The following call graphs should help illustrate some of the main IIO
+core dependencies:
+
++----------------------+
+| iio_counter_register |
++----------------------+
+  |  |  |
+  |  |  +-----------------------------+
+  |  +------------------+             |
+  |                     |             |
+  V                     V             V
++------------------+  +----------+  +---------------------+
+| iio_device_alloc |  | iio_priv |  | iio_device_register |
++------------------+  +----------+  +---------------------+
+
+The iio_counter_register function allocates and initializes a new
+iio_dev structure which will serve as the respective Counter's gateway
+to IIO core support. The address of the parent iio_counter structure is
+stored with the iio_dev structure via iio_priv in order to allow access
+back to the Counter from within the IIO core functions. Finally, the
+iio_dev structure is registered via iio_device_register.
+
++-----------------------+   +----------------------+
+| iio_read_channel_info |-->| iio_counter_read_raw |
++-----------------------+   +----------------------+
+                              |  |  |
+  +---------------------------+  |  |
+  |                +-------------+  |
+  |                |               ++
+  |                |               |
+  V                V               V
+  IIO_SIGNAL       IIO_COUNT       IIO_*
++-------------+  +------------+  +----------+
+| signal_read |  | value_read |  | read_raw |
++-------------+  +------------+  +----------+
+
++------------------------+   +-----------------------+
+| iio_write_channel_info |-->| iio_counter_write_raw |
++------------------------+   +-----------------------+
+                               |  |  |
+  +----------------------------+  |  |
+  |                 +-------------+  |
+  |                 |                |
+  |                 |                |
+  V                 V                V
+  IIO_SIGNAL        IIO_COUNT        IIO_*
++--------------+  +-------------+  +-----------+
+| signal_write |  | value_write |  | write_raw |
++--------------+  +-------------+  +-----------+
+
+Normally, the IIO core iio_read_channel_info and iio_write_channel_info
+functions respectiveluy call the driver-supplied read_raw and write_raw
+callbacks directly. Since the generic counter interface serves as an
+abstraction above IIO core, drive authors do not generally directly
+configure a read_raw/write_raw callback.
+
+Instead, the IIO Generic Counter Interface hooks on to the
+iio_read_channel_info and iio_write_channel_info expected read_raw and
+write_raw callbacks respectively via iio_counter_read_raw and
+iio_counter_write_raw. The iio_counter_read_raw and
+iio_counter_write_raw functions then call the respective driver-supplied
+signal_read/value_read and signal_write/value_write callbacks
+respectively for the appropriate IIO_SIGNAL OR IIO_COUNT. If an IIO core
+channel that was not part of the generic counter paradigm was supplied
+via the channels member of the iio_counter structure, then the
+respective driver-supplied (via the iio_counter structure info member)
+read_raw and write_raw are called.
+
++---------------------------+        +----------------------------+
+| iio_read_channel_ext_info |        | iio_write_channel_ext_info |
++---------------------------+        +----------------------------+
+  |                                    |
+  V                                    V
++-------------------------------+    +--------------------------------+
+| iio_counter_trigger_mode_read |    | iio_counter_trigger_mode_write |
++-------------------------------+    +--------------------------------+
+  |                                    |
+  V                                    V
++------------------+                 +------------------+
+| trigger_mode_get |                 | trigger_mode_set |
++------------------+                 +------------------+
+
++---------------+                     +----------------+
+| iio_enum_read |                     | iio_enum_write |
++---------------+                     +----------------+
+  |                                     |
+  V                                     V
++--------------------------------+    +--------------------------------+
+| iio_counter_value_function_get |    | iio_counter_value_function_set |
++--------------------------------+    +--------------------------------+
+  |                                     |
+  V                                     V
++--------------------+                +--------------------+
+| value_function_get |                | value_function_set |

This patch introduces the IIO generic counter interface for supporting counter devices. The generic counter interface serves as a catch-all to enable rudimentary support for devices that qualify as counters. More specific and apt counter interfaces may be developed on top of the generic counter interface, and those interfaces should be used by drivers when possible rather than the generic counter interface.

In the context of the IIO generic counter interface, a counter is defined as a device that reports one or more "counter values" based on the state changes of one or more "counter signals" as evaluated by a defined "counter function."

The IIO generic counter interface piggybacks off of the IIO core. This is primarily used to leverage the existing sysfs setup: the IIO_COUNT channel attributes represent the Counter Value, while the IIO_SIGNAL channel attributes represent the Counter Signal; auxilary IIO_COUNT attributes represent the Counter Signal connections (Triggers) and their respective state change configurations which trigger an associated "counter function" evaluation.

The iio_counter_ops structure serves as a container for driver callbacks to communicate with the device; function callbacks are provided to read and write various Signals and Values, and set and get the "trigger mode" and "function mode" for various Triggers and Values respectively.

To support a counter device, a driver must first allocate the available Counter Signals via iio_counter_signal structures. These Signals should be stored as an array and set to the signals array member of an allocated iio_counter structure before the Counter is registered to the system.

Counter Values may be allocated via iio_counter_value structures, and respective Counter Signal associations (Triggers) made via iio_counter_trigger structures. Associated iio_counter_trigger structures are stored as an array and set to the the triggers array member of the respective iio_counter_value structure. These iio_counter_value structures are set to the values array member of an allocated iio_counter structure before the Counter is registered to the system.

A counter device is registered to the system by passing the respective initialized iio_counter structure to the iio_counter_register function; similarly, the iio_counter_unregister function unregisters the respective counter. The devm_iio_counter_register and iio_devm_iio_counter_unregister functions serve as device memory-managed versions of the iio_counter_register and iio_counter unregister functions respectively.

Signed-off-by William Breathitt Gray <[email protected]>

---
 MAINTAINERS                        |   7 +
 drivers/iio/Kconfig                |   8 +
 drivers/iio/Makefile               |   1 +
 drivers/iio/counter/Kconfig        |   1 +
 drivers/iio/industrialio-counter.c | 900 +++++++++++++++++++++++++++++++++++++
 include/linux/iio/counter.h        | 166 +++++++
 6 files changed, 1083 insertions(+)
 create mode 100644 drivers/iio/industrialio-counter.c
 create mode 100644 include/linux/iio/counter.h

MAINTAINERS +0 -0

index 2281af4b41b6..8b7c37bed252 100644

MAINTAINERS +1 -0

+
 IIO MULTIPLEXER
 M:	Peter Rosin <[email protected]>
 L:	[email protected]

drivers/iio/Kconfig +8 -0

index b3c8c6ef0dff..78e01f4f5937 100644
@@ -30,6 +30,14 @@ config IIO_CONFIGFS
 	  (e.g. software triggers). For more info see
 	  Documentation/iio/iio_configfs.txt.
 
+config IIO_COUNTER
+	bool "Enable IIO counter support"
+	help
+	  Provides IIO core support for counters. This API provides
+	  a generic interface that serves as the building blocks to
+	  create more complex counter interfaces. Rudimentary support
+	  for counters is enabled.
+
 config IIO_TRIGGER
 	bool "Enable triggered sampling support"
 	help

drivers/iio/Makefile +1 -0

index 93c769cd99bf..6427ff38f964 100644
@@ -5,6 +5,7 @@
 obj-$(CONFIG_IIO) += industrialio.o
 industrialio-y := industrialio-core.o industrialio-event.o inkern.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
+industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
 
 obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o

drivers/iio/counter/Kconfig +1 -0

index 474e1ac4e7c0..c8becfe78e28 100644
@@ -4,6 +4,7 @@
 # When adding new entries keep the list in alphabetical order
 
 menu "Counters"
+	depends on IIO_COUNTER
 
 config 104_QUAD_8
 	tristate "ACCES 104-QUAD-8 driver"

drivers/iio/industrialio-counter.c new file +55 -0

new file mode 100644
index 000000000000..dfb982dae3a8
@@ -0,0 +1,900 @@
+/*
+ * Industrial I/O counter interface functions
+ * Copyright (C) 2017 William Breathitt Gray
+ *
+ * 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.
+ *
+ * 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/device.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/types.h>
+
+#include <linux/iio/counter.h>
+
+#define iio_priv_get_counter(_indio_dev) \
+	(*(struct iio_counter **)iio_priv(_indio_dev))
+
+static struct iio_counter_signal *iio_counter_signal_find_by_id(
+	const struct iio_counter *const counter, const int id)
+{
+	size_t i;
+	struct iio_counter_signal *signal;
+
+	for (i = 0; i < counter->num_signals; i++) {
+		signal = counter->signals + i;
+		if (signal->id == id)
+			return signal;
+	}
+
+	return NULL;
+}
+
+static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
+	const struct iio_counter_value *const value, const int id)
+{
+	size_t i;
+	struct iio_counter_trigger *trigger;
+
+	for (i = 0; i < value->num_triggers; i++) {
+		trigger = value->triggers + i;
+		if (trigger->signal->id == id)
+			return trigger;

drivers/iio/industrialio-counter.c new file +24 -0

+
+	for (i = 0; i < counter->num_values; i++) {
+		value = counter->values + i;
+		if (value->id == id)
+			return value;
+	}
+
+	return NULL;
+}
+
+static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	const struct iio_counter_signal *signal;
+
+	signal = iio_counter_signal_find_by_id(counter, chan->channel2);
+	if (!signal)
+		return -EINVAL;
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
+}
+
+static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,

drivers/iio/industrialio-counter.c new file +153 -0

+}
+
+static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_value *value;
+	size_t i;
+	const struct iio_counter_trigger *trigger;
+	ssize_t len = 0;
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value)
+		return -EINVAL;
+
+	/* Print out a list of every Signal association to Value */
+	for (i = 0; i < value->num_triggers; i++) {
+		trigger = value->triggers + i;
+		len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
+			trigger->signal->id, trigger->signal->name,
+			trigger->trigger_modes[trigger->mode]);
+		if (len >= PAGE_SIZE)
+			return -ENOMEM;
+	}
+
+	return len;
+}
+
+static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_value *value;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	int mode;
+
+	if (!counter->ops->trigger_mode_get)
+		return -EINVAL;
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value)
+		return -EINVAL;
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger)
+		return -EINVAL;
+
+	mode = counter->ops->trigger_mode_get(counter, value, trigger);
+
+	if (mode < 0)
+		return mode;
+	else if (mode >= trigger->num_trigger_modes)
+		return -EINVAL;
+
+	trigger->mode = mode;
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
+}
+
+static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
+	size_t len)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_value *value;
+	ssize_t err;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	unsigned int mode;
+
+	if (!counter->ops->trigger_mode_set)
+		return -EINVAL;
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value)
+		return -EINVAL;
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger)
+		return -EINVAL;
+
+	for (mode = 0; mode < trigger->num_trigger_modes; mode++)
+		if (sysfs_streq(buf, trigger->trigger_modes[mode]))
+			break;
+
+	if (mode >= trigger->num_trigger_modes)
+		return -EINVAL;
+
+	err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
+	if (err)
+		return err;
+
+	trigger->mode = mode;
+
+	return len;
+}
+
+static ssize_t iio_counter_trigger_mode_available_read(
+	struct iio_dev *indio_dev, uintptr_t priv,
+	const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_value *value;
+	ssize_t len = 0;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	unsigned int i;
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value)
+		return -EINVAL;
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger)
+		return -EINVAL;
+
+	for (i = 0; i < trigger->num_trigger_modes; i++)
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
+			trigger->trigger_modes[i]);
+
+	buf[len - 1] = '\n';
+
+	return len;
+}
+
+static int iio_counter_value_function_set(struct iio_dev *indio_dev,
+	const struct iio_chan_spec *chan, unsigned int mode)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_value *value;
+	int err;
+
+	if (!counter->ops->value_function_set)
+		return -EINVAL;
+
+	/* Find relevant Value */
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value)
+		return -EINVAL;
+
+	/* Map IIO core function_set to Generic Counter value_function_set */
+	err = counter->ops->value_function_set(counter, value, mode);
+	if (err)
+		return err;
+
+	value->mode = mode;
+
+	return 0;
+}
+
+static int iio_counter_value_function_get(struct iio_dev *indio_dev,
+	const struct iio_chan_spec *chan)

drivers/iio/industrialio-counter.c new file +142 -0

+	if (!value)
+		return -EINVAL;
+
+	/* Map IIO core function_get to Generic Counter value_function_get */
+	retval = counter->ops->value_function_get(counter, value);
+	if (retval < 0)
+		return retval;
+	else if (retval >= value->num_function_modes)
+		return -EINVAL;
+
+	value->mode = retval;
+
+	return retval;
+}
+
+static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
+	struct iio_counter_value *const value)
+{
+	const struct iio_chan_spec_ext_info ext_info_default[] = {
+		{
+			.name = "name",
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_value_name_read
+		},
+		IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
+		{
+			.name = "function_available",
+			.shared = IIO_SEPARATE,
+			.read = iio_enum_available_read,
+			.private = (void *)&value->function_enum
+		},
+		{
+			.name = "triggers",
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_value_triggers_read
+		}
+	};
+	const size_t num_default = ARRAY_SIZE(ext_info_default);
+	const struct iio_chan_spec_ext_info ext_info_trigger[] = {
+		{
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_trigger_mode_read,
+			.write = iio_counter_trigger_mode_write
+		},
+		{
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_trigger_mode_available_read
+		}
+	};
+	const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
+	const size_t num_triggers_ext_info = num_ext_info_trigger *
+		value->num_triggers;
+	const size_t num_ext_info = num_default + num_triggers_ext_info + 1;
+	int err;
+	struct iio_chan_spec_ext_info *ext_info;
+	const struct iio_counter_trigger *trigger;
+	size_t i;
+	size_t j;
+
+	/* Construct function_enum for Value */
+	value->function_enum.items = value->function_modes;
+	value->function_enum.num_items = value->num_function_modes;
+	value->function_enum.set = iio_counter_value_function_set;
+	value->function_enum.get = iio_counter_value_function_get;
+
+	ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
+	if (!ext_info)
+		return -ENOMEM;
+	ext_info[num_ext_info - 1].name = NULL;
+
+	/* Add ext_info for the name, function, function_available, and triggers
+	 * attributes
+	 */
+	memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
+	/* Add ext_info for the trigger_signalX-Z and
+	 * trigger_signalX-Z_available attributes for each Trigger
+	 */
+	for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
+		memcpy(ext_info + num_default + i, ext_info_trigger,
+			sizeof(ext_info_trigger));
+
+	/* Set name for each trigger_signalX-Z and trigger_signalX-Z_available
+	 * attribute; store the respective Signal ID address in each ext_info
+	 * private member
+	 */
+	for (i = num_default, j = 0; j < value->num_triggers; i++, j++) {
+		trigger = value->triggers + j;
+
+		ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
+			chan->channel, trigger->signal->id);
+		if (!ext_info[i].name) {
+			err = -ENOMEM;
+			goto err_name_alloc;
+		}
+		ext_info[i].private = (void *)&trigger->signal->id;
+		i++;
+
+		ext_info[i].name = kasprintf(GFP_KERNEL,
+			"trigger_signal%d-%d_available",
+			chan->channel, trigger->signal->id);
+		if (!ext_info[i].name) {
+			err = -ENOMEM;
+			goto err_name_alloc;
+		}
+		ext_info[i].private = (void *)&trigger->signal->id;
+	}
+
+	chan->ext_info = ext_info;
+
+	return 0;
+
+err_name_alloc:
+	while (i-- > num_default)
+		kfree(ext_info[i].name);
+	kfree(ext_info);
+	return err;
+}
+
+static void iio_counter_value_ext_info_free(
+	const struct iio_chan_spec *const channel)
+{
+	size_t i;
+	const char *const prefix = "trigger_signal";
+	const size_t prefix_len = strlen(prefix);
+
+	for (i = 0; channel->ext_info[i].name; i++)
+		if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
+			kfree(channel->ext_info[i].name);
+	kfree(channel->ext_info);
+}
+
+static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
+	{
+		.name = "name",
+		.shared = IIO_SEPARATE,
+		.read = iio_counter_signal_name_read
+	},
+	{}
+};
+
+static int iio_counter_channels_alloc(struct iio_counter *const counter)
+{

drivers/iio/industrialio-counter.c new file +11 -0

+	if (!channels)
+		return -ENOMEM;
+
+	/* If any channels were supplied on Counter registration,
+	 * we add them here to the front of the array
+	 */
+	memcpy(channels, counter->channels,
+		counter->num_channels * sizeof(*counter->channels));
+
+	/* Add channel for each Value */
+	for (j = 0; j < counter->num_values; j++) {

drivers/iio/industrialio-counter.c new file +97 -0

+		err = iio_counter_value_ext_info_alloc(channels + i, value);
+		if (err)
+			goto err_value_ext_info_alloc;
+
+		i++;
+	}
+
+	/* Add channel for each Signal */
+	for (j = 0; j < counter->num_signals; j++) {
+		signal = counter->signals + j;
+
+		channels[i].type = IIO_SIGNAL;
+		channels[i].channel = counter->id;
+		channels[i].channel2 = signal->id;
+		channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+		channels[i].indexed = 1;
+		channels[i].counter = 1;
+		channels[i].ext_info = iio_counter_signal_ext_info;
+
+		i++;
+	}
+
+	counter->indio_dev->num_channels = num_channels;
+	counter->indio_dev->channels = channels;
+
+	return 0;
+
+err_value_ext_info_alloc:
+	while (i-- > counter->num_channels)
+		iio_counter_value_ext_info_free(channels + i);
+	kfree(channels);
+	return err;
+}
+
+static void iio_counter_channels_free(const struct iio_counter *const counter)
+{
+	size_t i = counter->num_channels + counter->indio_dev->num_channels;
+	const struct iio_chan_spec *const chans = counter->indio_dev->channels;
+
+	while (i-- > counter->num_channels)
+		/* Only IIO_COUNT channels need to be freed here */
+		if (chans[i].type == IIO_COUNT)
+			iio_counter_value_ext_info_free(chans + i);
+
+	kfree(chans);
+}
+
+static int iio_counter_read_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int *val, int *val2, long mask)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_signal *signal;
+	struct iio_counter_value *value;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	switch (chan->type) {
+	/* Map read_raw to signal_read for Signal */
+	case IIO_SIGNAL:
+		if (!counter->ops->signal_read)
+			return -EINVAL;
+
+		signal = iio_counter_signal_find_by_id(counter, chan->channel2);
+		if (!signal)
+			return -EINVAL;
+
+		return counter->ops->signal_read(counter, signal, val, val2);
+	/* Map read_raw to value_read for Value */
+	case IIO_COUNT:
+		if (!counter->ops->value_read)
+			return -EINVAL;
+
+		value = iio_counter_value_find_by_id(counter, chan->channel2);
+		if (!value)
+			return -EINVAL;
+
+		return counter->ops->value_read(counter, value, val, val2);
+	/* Map read_raw to read_raw for non-counter channel */
+	default:
+		if (counter->info && counter->info->read_raw)
+			return counter->info->read_raw(indio_dev, chan, val,
+				val2, mask);
+	}
+
+	return -EINVAL;
+}
+
+static int iio_counter_write_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int val, int val2, long mask)
+{
+	struct iio_counter *const counter = iio_priv_get_counter(indio_dev);
+	struct iio_counter_signal *signal;
+	struct iio_counter_value *value;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;

drivers/iio/industrialio-counter.c new file +36 -0

+		if (!value)
+			return -EINVAL;
+
+		return counter->ops->value_write(counter, value, val, val2);
+	/* Map write_raw to write_raw for non-counter channel */
+	default:
+		if (counter->info && counter->info->write_raw)
+			return counter->info->write_raw(indio_dev, chan, val,
+				val2, mask);
+	}
+
+	return -EINVAL;
+}
+
+static int iio_counter_signals_validate(const struct iio_counter *const counter)
+{
+	size_t i;
+	const struct iio_counter_signal *signal;
+	size_t j;
+	int curr_id;
+
+	/* At least one Signal must be defined */
+	if (!counter->num_signals || !counter->signals) {
+		pr_err("Counter '%d' Signals undefined\n", counter->id);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < counter->num_signals; i++) {
+		signal = counter->signals + i;
+		/* No two Signals may share the same ID */
+		for (j = 0; j < i; j++) {
+			curr_id = counter->signals[j].id;
+			if (curr_id == signal->id) {
+				pr_err("Duplicate Counter '%d' Signal '%d'\n",
+						counter->id, signal->id);
+				return -EEXIST;

drivers/iio/industrialio-counter.c new file +12 -0

+	}
+
+	return 0;
+}
+
+static int iio_counter_triggers_validate(const int counter_id,
+	const struct iio_counter_value *const value)
+{
+	size_t i;
+	const struct iio_counter_trigger *trigger;
+	size_t j;
+	int curr_id;

drivers/iio/industrialio-counter.c new file +20 -0

+	 */
+	for (i = 0; i < value->num_triggers; i++)
+		if (!value->triggers[i].signal) {
+			pr_err("Counter '%d' Trigger '%zu' Signal undefined\n",
+				counter_id, i);
+			return -EINVAL;
+		}
+
+	/* Verify validity of each Trigger */
+	for (i = 0; i < value->num_triggers; i++) {
+		trigger = value->triggers + i;
+		/* No two Trigger Signals may share the same ID */
+		for (j = 0; j < i; j++) {
+			curr_id = value->triggers[j].signal->id;
+			if (curr_id == trigger->signal->id) {
+				pr_err("Signal '%d' is already linked to Counter '%d' Value '%d'\n",
+					trigger->signal->id, counter_id,
+					value->id);
+				return -EEXIST;
+			}

drivers/iio/industrialio-counter.c new file +4 -0

+
+		/* At least one trigger mode must be defined for each Trigger */
+		if (!trigger->num_trigger_modes || !trigger->trigger_modes) {
+			pr_err("Counter '%d' Signal '%d' trigger modes undefined\n",

drivers/iio/industrialio-counter.c new file +7 -0

+	size_t i;
+	const struct iio_counter_value *value;
+	size_t j;
+	int curr_id;
+	int err;
+
+	/* At least one Value must be defined */

drivers/iio/industrialio-counter.c new file +52 -0

+			curr_id = counter->values[j].id;
+			if (curr_id == value->id) {
+				pr_err("Duplicate Counter '%d' Value '%d'\n",
+					counter->id, value->id);
+				return -EEXIST;
+			}
+		}
+		for (j = i + 1; j < counter->num_values; j++) {
+			curr_id = counter->values[j].id;
+			if (curr_id == value->id) {
+				pr_err("Duplicate Counter '%d' Value '%d'\n",
+					counter->id, value->id);
+				return -EEXIST;
+			}
+		}
+
+		/* At least one function mode must be defined for each Value */
+		if (!value->num_function_modes || !value->function_modes) {
+			pr_err("Counter '%d' Value '%d' function modes undefined\n",
+				counter->id, value->id);
+			return -EINVAL;
+		}
+
+		/* Verify the Triggers associated with each Value */
+		err = iio_counter_triggers_validate(counter->id, value);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+/**
+ * iio_counter_register - register Counter to the system
+ * @counter: pointer to IIO Counter to register
+ *
+ * This function piggybacks off of iio_device_register. First, the relevant
+ * Counter members are validated; the signals and values members must be defined
+ * and populated by valid Signal and Value structures respectively. Next, a
+ * struct iio_dev is allocated by a call to iio_device_alloc and initialized for
+ * the Counter, IIO channels are allocated, the Counter address is stored as the
+ * private data, and finally iio_device_register is called.
+ */
+int iio_counter_register(struct iio_counter *const counter)
+{
+	const struct iio_info info_default = {
+		.read_raw = iio_counter_read_raw,
+		.write_raw = iio_counter_write_raw
+	};
+	int err;
+	struct iio_info *info;
+	struct iio_counter **priv;

drivers/iio/industrialio-counter.c new file +159 -0

+	 * Triggers for each Value are also verified for validity
+	 */
+	err = iio_counter_values_validate(counter);
+	if (err)
+		return err;
+
+	counter->indio_dev = iio_device_alloc(sizeof(counter));
+	if (!counter->indio_dev)
+		return -ENOMEM;
+
+	info = kmalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		err = -ENOMEM;
+		goto err_info_alloc;
+	}
+	/* If an iio_info has been supplied than we use that,
+	 * otherwise we set all callbacks to NULL; iio_counter_read_raw
+	 * and iio_counter_write_raw is used for read_raw and write_raw
+	 * for either case in order to support counter functionality
+	 * (supplied read_raw/write_raw will be called from within
+	 * iio_counter_read_raw/iio_counter_write_raw for non-counter
+	 * channels)
+	 */
 
+	if (counter->info) {
+		memcpy(info, counter->info, sizeof(*counter->info));
+		info->read_raw = iio_counter_read_raw;
+		info->write_raw = iio_counter_write_raw;
+	} else {
+		memcpy(info, &info_default, sizeof(info_default));
+	}
+
+	counter->indio_dev->info = info;
+	counter->indio_dev->modes = INDIO_DIRECT_MODE;
+	counter->indio_dev->name = counter->name;
+	counter->indio_dev->dev.parent = counter->dev;
+
+	/* IIO channels are allocated and set for Signals, Values, and Triggers;
+	 * any auxiliary IIO channels provided in iio_counter are also set
+	 */
+	err = iio_counter_channels_alloc(counter);
+	if (err)
+		goto err_channels_alloc;
+
+	/* Pointer to the counter is stored in indio_dev as a way to refer
+	 * back to the counter from within various IIO callbacks
+	 */
+	priv = iio_priv(counter->indio_dev);
+	memcpy(priv, &counter, sizeof(*priv));
+
+	err = iio_device_register(counter->indio_dev);
+	if (err)
+		goto err_iio_device_register;
+
+	return 0;
+
+err_iio_device_register:
+	iio_counter_channels_free(counter);
+err_channels_alloc:
+	kfree(info);
+err_info_alloc:
+	iio_device_free(counter->indio_dev);
+	return err;
+}
+EXPORT_SYMBOL(iio_counter_register);
+
+/**
+ * iio_counter_unregister - unregister Counter from the system
+ * @counter: pointer to IIO Counter to unregister
+ *
+ * The Counter is unregistered from the system. The indio_dev is unregistered
+ * and all allocated memory is freed.
+ */
+void iio_counter_unregister(struct iio_counter *const counter)
+{
+	const struct iio_info *const info = counter->indio_dev->info;
+
+	if (!counter)
+		return;
+
+	iio_device_unregister(counter->indio_dev);
+
+	iio_counter_channels_free(counter);
+
+	kfree(info);
+	iio_device_free(counter->indio_dev);
+}
+EXPORT_SYMBOL(iio_counter_unregister);
+
+static void devm_iio_counter_unreg(struct device *dev, void *res)
+{
+	iio_counter_unregister(*(struct iio_counter **)res);
+}
+
+/**
+ * devm_iio_counter_register - Resource-managed iio_counter_register
+ * @dev: Device to allocate iio_counter for
+ * @counter: pointer to IIO Counter to register
+ *
+ * Managed iio_counter_register. The IIO counter registered with this
+ * function is automatically unregistered on driver detach. This function
+ * calls iio_counter_register internally. Refer to that function for more
+ * information.
+ *
+ * If an iio counter registered with this function needs to be unregistered
+ * separately, devm_iio_counter_unregister must be used.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_iio_counter_register(struct device *dev,
+	struct iio_counter *const counter)
+{
+	struct iio_counter **ptr;
+	int ret;
+
+	ptr = devres_alloc(devm_iio_counter_unreg, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return -ENOMEM;
+
+	*ptr = counter;
+	ret = iio_counter_register(counter);
+	if (!ret)
+		devres_add(dev, ptr);
+	else
+		devres_free(ptr);
+
+	return ret;
+}
+EXPORT_SYMBOL(devm_iio_counter_register);
+
+static int devm_iio_counter_match(struct device *dev, void *res, void *data)
+{
+	struct iio_counter **r = res;
+
+	if (!r || !*r) {
+		WARN_ON(!r || !*r);
+		return 0;
+	}
+
+	return *r == data;
+}
+
+/**
+ * devm_iio_counter_unregister - Resource-managed iio_counter_unregister
+ * @dev: Device this iio_counter belongs to
+ * @counter: the iio counter associated with the device
+ *
+ * Unregister iio counter registered with devm_iio_counter_register.
+ */
+void devm_iio_counter_unregister(struct device *dev,
+	struct iio_counter *const counter)
+{
+	int rc;
+
+	rc = devres_release(dev, devm_iio_counter_unreg,
+		devm_iio_counter_match, counter);
+	WARN_ON(rc);
+}
+EXPORT_SYMBOL(devm_iio_counter_unregister);

include/linux/iio/counter.h new file +35 -0

new file mode 100644
index 000000000000..35645406711a
@@ -0,0 +1,166 @@
+/*
+ * Industrial I/O counter interface
+ * Copyright (C) 2017 William Breathitt Gray
+ *
+ * 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.
+ *
+ * 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.
+ */
+#ifndef _IIO_COUNTER_H_
+#define _IIO_COUNTER_H_
+
+#ifdef CONFIG_IIO_COUNTER
+
+#include <linux/device.h>
+#include <linux/types.h>
+
+#include <linux/iio/iio.h>
+
+/**
+ * struct iio_counter_signal - IIO Counter Signal node
+ * @id:		[DRIVER] unique ID used to identify signal
+ * @name:	[DRIVER] device-specific signal name
+ */
+struct iio_counter_signal {
+	int		id;
+	const char	*name;
+};
+
+/**
+ * struct iio_counter_trigger - IIO Counter Trigger node

include/linux/iio/counter.h new file +24 -0

+};
+
+/**
+ * struct iio_counter_value - IIO Counter Value node
+ * @id:			[DRIVER] unique ID used to identify value
+ * @name:		[DRIVER] device-specific value name
+ * @mode:		[DRIVER] current function mode state
+ * @function_modes:	[DRIVER] available function modes
+ * @num_function_modes:	[DRIVER] number of modes specified in @function_modes
+ * @triggers:		[DRIVER] array of triggers for initialization
+ * @num_triggers:	[DRIVER] number of triggers specified in @triggers
+ * @function_enum:	[INTERN] used internally to generate function attributes
+ */
+struct iio_counter_value {
+	int			id;
+	const char		*name;
+	unsigned int		mode;
+	const char *const	*function_modes;
+	unsigned int		num_function_modes;
+
+	struct iio_counter_trigger	*triggers;
+	size_t				num_triggers;
+
+	struct iio_enum		function_enum;

include/linux/iio/counter.h new file +47 -0

+ * @trigger_mode_set:	function to set the trigger mode. mode is the index of
+ *			the requested mode from the value trigger_modes array.
+ * @trigger_mode_get:	function to get the current trigger mode. Return value
+ *			will specify the index of the current mode from the
+ *			value trigger_modes array.
+ * @value_read:		function to request a value value from the device.
+ *			Return value will specify the type of value returned by
+ *			the device. val and val2 will contain the elements
+ *			making up the returned value.
+ * @value_write:	function to write a value value to the device.
+ *                      Parameters are interpreted the same as value_read.
+ * @value_function_set: function to set the value function mode. mode is the
+ *			index of the requested mode from the value
+ *			function_modes array.
+ * @value_function_get: function to get the current value function mode. Return
+ *			value will specify the index of the current mode from
+ *			the value function_modes array.
+ */
+struct iio_counter_ops {
+	int (*signal_read)(struct iio_counter *counter,
+		struct iio_counter_signal *signal, int *val, int *val2);
+	int (*signal_write)(struct iio_counter *counter,
+		struct iio_counter_signal *signal, int val, int val2);
+	int (*trigger_mode_set)(struct iio_counter *counter,
+		struct iio_counter_value *value,
+		struct iio_counter_trigger *trigger, unsigned int mode);
+	int (*trigger_mode_get)(struct iio_counter *counter,
+		struct iio_counter_value *value,
+		struct iio_counter_trigger *trigger);
+	int (*value_read)(struct iio_counter *counter,
+		struct iio_counter_value *value, int *val, int *val2);
+	int (*value_write)(struct iio_counter *counter,
+		struct iio_counter_value *value, int val, int val2);
+	int (*value_function_set)(struct iio_counter *counter,
+		struct iio_counter_value *value, unsigned int mode);
+	int (*value_function_get)(struct iio_counter *counter,
+		struct iio_counter_value *value);
+};
+
+/**
+ * struct iio_counter - IIO Counter data structure
+ * @id:			[DRIVER] unique ID used to identify counter
+ * @name:		[DRIVER] name of the device
+ * @dev:		[DRIVER] device structure, should be assigned a parent
+ *			and owner
+ * @ops:		[DRIVER] callbacks from driver for counter components
+ * @signals:		[DRIVER] array of signals for initialization

include/linux/iio/counter.h new file +28 -0

+	int				id;
+	const char			*name;
+	struct device			*dev;
+	const struct iio_counter_ops	*ops;
+
+	struct iio_counter_signal	*signals;
+	size_t				num_signals;
+	struct iio_counter_value	*values;
+	size_t				num_values;
+
+	const struct iio_chan_spec	*channels;
+	size_t				num_channels;
+	const struct iio_info		*info;
+
+	struct iio_dev	*indio_dev;
+	void		*driver_data;
+};
+
+int iio_counter_register(struct iio_counter *const counter);
+void iio_counter_unregister(struct iio_counter *const counter);
+int devm_iio_counter_register(struct device *dev,
+	struct iio_counter *const counter);
+void devm_iio_counter_unregister(struct device *dev,
+	struct iio_counter *const counter);
+
+#endif /* CONFIG_IIO_COUNTER */
+
+#endif /* _IIO_COUNTER_H_ */