iio: position: Add support for Azoteq IQS624/625 angle sensors

This patch adds support for the Azoteq IQS624 and IQS625 angular position
sensors, capable of reporting the angle of a rotating shaft down to 1 and
10 degrees of accuracy, respectively.

This patch also introduces a home for linear and angular position sensors.
Unlike resolvers, they are typically contactless and use the Hall effect.

Signed-off-by: Jeff LaBundy <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/iio/Kconfig

···
 if IIO_TRIGGER
    source "drivers/iio/trigger/Kconfig"
 endif #IIO_TRIGGER
+source "drivers/iio/position/Kconfig"
 source "drivers/iio/potentiometer/Kconfig"
 source "drivers/iio/potentiostat/Kconfig"
 source "drivers/iio/pressure/Kconfig"

drivers/iio/Makefile

···
 obj-y += magnetometer/
 obj-y += multiplexer/
 obj-y += orientation/
+obj-y += position/
 obj-y += potentiometer/
 obj-y += potentiostat/
 obj-y += pressure/

drivers/iio/position/Kconfig

···
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Linear and angular position sensors
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Linear and angular position sensors"
+
+config IQS624_POS
+	tristate "Azoteq IQS624/625 angular position sensors"
+	depends on MFD_IQS62X || COMPILE_TEST
+	help
+	  Say Y here if you want to build support for the Azoteq IQS624
+	  and IQS625 angular position sensors.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called iqs624-pos.
+
+endmenu

drivers/iio/position/Makefile

···
+#
+# Makefile for IIO linear and angular position sensors
+#
+
+# When adding new entries keep the list in alphabetical order
+
+obj-$(CONFIG_IQS624_POS)	+= iqs624-pos.o

drivers/iio/position/iqs624-pos.c

···
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Azoteq IQS624/625 Angular Position Sensors
+ *
+ * Copyright (C) 2019 Jeff LaBundy <[e-mail]>
+ */
+
+#include <linux/device.h>
+#include <linux/iio/events.h>
+#include <linux/iio/iio.h>
+#include <linux/kernel.h>
+#include <linux/mfd/iqs62x.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define IQS624_POS_DEG_OUT			0x16
+
+#define IQS624_POS_SCALE1			(314159 / 180)
+#define IQS624_POS_SCALE2			100000
+
+struct iqs624_pos_private {
+	struct iqs62x_core *iqs62x;
+	struct notifier_block notifier;
+	struct mutex lock;
+	bool angle_en;
+	u16 angle;
+};
+
+static int iqs624_pos_angle_en(struct iqs62x_core *iqs62x, bool angle_en)
+{
+	unsigned int event_mask = IQS624_HALL_UI_WHL_EVENT;
+
+	/*
+	 * The IQS625 reports angular position in the form of coarse intervals,
+	 * so only interval change events are unmasked. Conversely, the IQS624
+	 * reports angular position down to one degree of resolution, so wheel
+	 * movement events are unmasked instead.
+	 */
+	if (iqs62x->dev_desc->prod_num == IQS625_PROD_NUM)
+		event_mask = IQS624_HALL_UI_INT_EVENT;
+
+	return regmap_update_bits(iqs62x->regmap, IQS624_HALL_UI, event_mask,
+				  angle_en ? 0 : 0xFF);
+}
+
+static int iqs624_pos_notifier(struct notifier_block *notifier,
+			       unsigned long event_flags, void *context)
+{
+	struct iqs62x_event_data *event_data = context;
+	struct iqs624_pos_private *iqs624_pos;
+	struct iqs62x_core *iqs62x;
+	struct iio_dev *indio_dev;
+	u16 angle = event_data->ui_data;
+	s64 timestamp;
+	int ret;
+
+	iqs624_pos = container_of(notifier, struct iqs624_pos_private,
+				  notifier);
+	indio_dev = iio_priv_to_dev(iqs624_pos);
+	timestamp = iio_get_time_ns(indio_dev);
+
+	iqs62x = iqs624_pos->iqs62x;
+	if (iqs62x->dev_desc->prod_num == IQS625_PROD_NUM)
+		angle = event_data->interval;
+
+	mutex_lock(&iqs624_pos->lock);
+
+	if (event_flags & BIT(IQS62X_EVENT_SYS_RESET)) {
+		ret = iqs624_pos_angle_en(iqs62x, iqs624_pos->angle_en);
+		if (ret) {
+			dev_err(indio_dev->dev.parent,
+				"Failed to re-initialize device: %d\n", ret);
+			ret = NOTIFY_BAD;
+		} else {
+			ret = NOTIFY_OK;
+		}
+	} else if (iqs624_pos->angle_en && (angle != iqs624_pos->angle)) {
+		iio_push_event(indio_dev,
+			       IIO_UNMOD_EVENT_CODE(IIO_ANGL, 0,
+						    IIO_EV_TYPE_CHANGE,
+						    IIO_EV_DIR_NONE),
+			       timestamp);
+
+		iqs624_pos->angle = angle;
+		ret = NOTIFY_OK;
+	} else {
+		ret = NOTIFY_DONE;
+	}
+
+	mutex_unlock(&iqs624_pos->lock);
+
+	return ret;
+}
+
+static void iqs624_pos_notifier_unregister(void *context)
+{
+	struct iqs624_pos_private *iqs624_pos = context;
+	struct iio_dev *indio_dev = iio_priv_to_dev(iqs624_pos);
+	int ret;
+
+	ret = blocking_notifier_chain_unregister(&iqs624_pos->iqs62x->nh,
+						 &iqs624_pos->notifier);
+	if (ret)
+		dev_err(indio_dev->dev.parent,
+			"Failed to unregister notifier: %d\n", ret);
+}
+
+static int iqs624_pos_angle_get(struct iqs62x_core *iqs62x, unsigned int *val)
+{
+	int ret;
+	__le16 val_buf;
+
+	if (iqs62x->dev_desc->prod_num == IQS625_PROD_NUM)
+		return regmap_read(iqs62x->regmap, iqs62x->dev_desc->interval,
+				   val);
+
+	ret = regmap_raw_read(iqs62x->regmap, IQS624_POS_DEG_OUT, &val_buf,
+			      sizeof(val_buf));
+	if (ret)
+		return ret;
+
+	*val = le16_to_cpu(val_buf);
+
+	return 0;
+}
+
+static int iqs624_pos_read_raw(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       int *val, int *val2, long mask)
+{
+	struct iqs624_pos_private *iqs624_pos = iio_priv(indio_dev);
+	struct iqs62x_core *iqs62x = iqs624_pos->iqs62x;
+	unsigned int scale = 1;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iqs624_pos_angle_get(iqs62x, val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		if (iqs62x->dev_desc->prod_num == IQS625_PROD_NUM) {
+			ret = regmap_read(iqs62x->regmap, IQS624_INTERVAL_DIV,
+					  &scale);
+			if (ret)
+				return ret;
+		}
+
+		*val = scale * IQS624_POS_SCALE1;
+		*val2 = IQS624_POS_SCALE2;
+		return IIO_VAL_FRACTIONAL;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int iqs624_pos_read_event_config(struct iio_dev *indio_dev,
+					const struct iio_chan_spec *chan,
+					enum iio_event_type type,
+					enum iio_event_direction dir)
+{
+	struct iqs624_pos_private *iqs624_pos = iio_priv(indio_dev);
+	int ret;
+
+	mutex_lock(&iqs624_pos->lock);
+	ret = iqs624_pos->angle_en;
+	mutex_unlock(&iqs624_pos->lock);
+
+	return ret;
+}
+
+static int iqs624_pos_write_event_config(struct iio_dev *indio_dev,
+					 const struct iio_chan_spec *chan,
+					 enum iio_event_type type,
+					 enum iio_event_direction dir,
+					 int state)
+{
+	struct iqs624_pos_private *iqs624_pos = iio_priv(indio_dev);
+	struct iqs62x_core *iqs62x = iqs624_pos->iqs62x;
+	unsigned int val;
+	int ret;
+
+	mutex_lock(&iqs624_pos->lock);
+
+	ret = iqs624_pos_angle_get(iqs62x, &val);
+	if (ret)
+		goto err_mutex;
+
+	ret = iqs624_pos_angle_en(iqs62x, state);
+	if (ret)
+		goto err_mutex;
+
+	iqs624_pos->angle = val;
+	iqs624_pos->angle_en = state;
+
+err_mutex:
+	mutex_unlock(&iqs624_pos->lock);
+
+	return ret;
+}
+
+static const struct iio_info iqs624_pos_info = {
+	.read_raw = &iqs624_pos_read_raw,
+	.read_event_config = iqs624_pos_read_event_config,
+	.write_event_config = iqs624_pos_write_event_config,
+};
+
+static const struct iio_event_spec iqs624_pos_events[] = {
+	{
+		.type = IIO_EV_TYPE_CHANGE,
+		.dir = IIO_EV_DIR_NONE,
+		.mask_separate = BIT(IIO_EV_INFO_ENABLE),
+	},
+};
+
+static const struct iio_chan_spec iqs624_pos_channels[] = {
+	{
+		.type = IIO_ANGL,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.event_spec = iqs624_pos_events,
+		.num_event_specs = ARRAY_SIZE(iqs624_pos_events),
+	},
+};
+
+static int iqs624_pos_probe(struct platform_device *pdev)
+{
+	struct iqs62x_core *iqs62x = dev_get_drvdata(pdev->dev.parent);
+	struct iqs624_pos_private *iqs624_pos;
+	struct iio_dev *indio_dev;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*iqs624_pos));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	iqs624_pos = iio_priv(indio_dev);
+	iqs624_pos->iqs62x = iqs62x;
+
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->dev.parent = &pdev->dev;
+	indio_dev->channels = iqs624_pos_channels;
+	indio_dev->num_channels = ARRAY_SIZE(iqs624_pos_channels);
+	indio_dev->name = iqs62x->dev_desc->dev_name;
+	indio_dev->info = &iqs624_pos_info;
+
+	mutex_init(&iqs624_pos->lock);
+
+	iqs624_pos->notifier.notifier_call = iqs624_pos_notifier;
+	ret = blocking_notifier_chain_register(&iqs624_pos->iqs62x->nh,
+					       &iqs624_pos->notifier);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(&pdev->dev,
+				       iqs624_pos_notifier_unregister,
+				       iqs624_pos);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(&pdev->dev, indio_dev);
+}
+
+static struct platform_driver iqs624_pos_platform_driver = {
+	.driver = {
+		.name = "iqs624-pos",
+	},
+	.probe = iqs624_pos_probe,
+};
+module_platform_driver(iqs624_pos_platform_driver);
+
+MODULE_AUTHOR("Jeff LaBundy <[e-mail]>");
+MODULE_DESCRIPTION("Azoteq IQS624/625 Angular Position Sensors");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:iqs624-pos");