Date:   Thu, 16 Dec 2021 14:26:51 -0600
From:   frank zago <frank@...o.net>
To:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        frank zago <frank@...o.net>, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] iio: position: Add support for ams AS5600 angle sensor

The AS5600 is a Hall-based rotary magnetic position sensor using
planar sensors that convert the magnetic field component perpendicular
to the surface of the chip into a voltage, or a numerical value
available through i2c.

The driver registers the chip as an IIO_ANGL device. It also exposes
the various registers through sysfs.

Signed-off-by: frank zago <frank@...o.net>
---

I'm not certain the values the driver return to IIO are correct. The
angle returned by the chip is a value in 0..4095, and that's what the
driver returns. The sysfs doc says it should be in radian.

Also it's unclear to me how I should define the scale.


 .../ABI/testing/sysfs-bus-iio-position-as5600 |  38 +++
 drivers/iio/position/Kconfig                  |  10 +
 drivers/iio/position/Makefile                 |   1 +
 drivers/iio/position/as5600.c                 | 309 ++++++++++++++++++
 4 files changed, 358 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-position-as5600
 create mode 100644 drivers/iio/position/as5600.c

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-position-as5600 b/Documentation/ABI/testing/sysfs-bus-iio-position-as5600
new file mode 100644
index 000000000000..d0d9c794529b
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-position-as5600
@@ -0,0 +1,38 @@
+What:		sys/bus/iio/devices/iio:deviceX/in_angl0_raw
+KernelVersion:	TBD
+Contact:	linux-iio@...r.kernel.org
+Description:
+	Returns the unscaled and unmodified angle
+
+What:		sys/bus/iio/devices/iio:deviceX/in_angl1_raw
+KernelVersion:	TBD
+Contact:	linux-iio@...r.kernel.org
+Description:
+	Returns the scaled and modified angle, as affected by the
+	zpos/mpos/mang values.
+
+What:		sys/bus/iio/devices/iio:deviceX/agc
+What:		sys/bus/iio/devices/iio:deviceX/conf_fth
+What:		sys/bus/iio/devices/iio:deviceX/conf_hyst
+What:		sys/bus/iio/devices/iio:deviceX/conf_outs
+What:		sys/bus/iio/devices/iio:deviceX/conf_pm
+What:		sys/bus/iio/devices/iio:deviceX/conf_pwmf
+What:		sys/bus/iio/devices/iio:deviceX/conf_sf
+What:		sys/bus/iio/devices/iio:deviceX/conf_wd
+What:		sys/bus/iio/devices/iio:deviceX/magnitude
+What:		sys/bus/iio/devices/iio:deviceX/mang
+What:		sys/bus/iio/devices/iio:deviceX/mpos
+What:		sys/bus/iio/devices/iio:deviceX/status_md
+What:		sys/bus/iio/devices/iio:deviceX/status_mh
+What:		sys/bus/iio/devices/iio:deviceX/status_ml
+What:		sys/bus/iio/devices/iio:deviceX/zmco
+What:		sys/bus/iio/devices/iio:deviceX/zpos
+KernelVersion:	TBD
+Contact:	linux-iio@...r.kernel.org
+Description:
+	Read and write the ams AS5600 internal registers and their
+	fields. zpos/mpos can be used to create a subset of the 0-360
+	degree range. status_md will tell whether the magnet is
+	detected. Check the datasheet
+	(https://ams.com/documents/20143/36005/AS5600_DS000365_5-00.pdf)
+	for more information.
diff --git a/drivers/iio/position/Kconfig b/drivers/iio/position/Kconfig
index 1576a6380b53..111ed551ae79 100644
--- a/drivers/iio/position/Kconfig
+++ b/drivers/iio/position/Kconfig
@@ -6,6 +6,16 @@

 menu "Linear and angular position sensors"

+config AS5600
+	tristate "ams AS5600 angular position sensor"
+	depends on I2C
+	help
+	  Say Y here if you want to build support for the ams 5600
+	  12-Bit Programmable Contactless Potentiometer.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called as5600.
+
 config IQS624_POS
 	tristate "Azoteq IQS624/625 angular position sensors"
 	depends on MFD_IQS62X || COMPILE_TEST
diff --git a/drivers/iio/position/Makefile b/drivers/iio/position/Makefile
index d70902f2979d..53930681e6a4 100644
--- a/drivers/iio/position/Makefile
+++ b/drivers/iio/position/Makefile
@@ -4,5 +4,6 @@

 # When adding new entries keep the list in alphabetical order

+obj-$(CONFIG_AS5600)		+= as5600.o
 obj-$(CONFIG_HID_SENSOR_CUSTOM_INTEL_HINGE) += hid-sensor-custom-intel-hinge.o
 obj-$(CONFIG_IQS624_POS)	+= iqs624-pos.o
diff --git a/drivers/iio/position/as5600.c b/drivers/iio/position/as5600.c
new file mode 100644
index 000000000000..2b160fd3a795
--- /dev/null
+++ b/drivers/iio/position/as5600.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * ams AS5600 -- 12-Bit Programmable Contactless Potentiometer
+ *
+ * Copyright 2021, Frank Zago
+ *
+ * datasheet v1.06 (2018-Jun-20):
+ *    https://ams.com/documents/20143/36005/AS5600_DS000365_5-00.pdf
+ *
+ * The rotating magnet is installed from 0.5mm to 3mm parallel to and
+ * above the chip.
+ *
+ * The raw angle value returned by the chip is [0..4095]. The channel
+ * 0 (in_angl0_raw) returns the unscaled and unmodified angle, always
+ * covering the 360 degrees. The channel 1 returns the chip adjusted
+ * angle, covering from 18 to 360 degrees, as modified by its
+ * ZPOS/MPOS/MANG values,
+ *
+ * ZPOS and MPOS can be programmed through their sysfs entries. The
+ * MANG register doesn't appear to be programmable without flashing
+ * the chip.
+ *
+ * If the DIR pin is grounded, angles will increase when the magnet is
+ * turned clockwise. If DIR is connected to Vcc, it will be the opposite.
+ *
+ * Permanent programming of the MPOS/ZPOS/MANG/CONF registers is not
+ * implemented.
+ *
+ * The i2c address of the device is 0x36.
+ */
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/i2c.h>
+#include <linux/delay.h>
+
+/* Registers and their fields, as defined in the datasheet */
+#define REG_ZMCO 0x00
+#define   REG_ZMCO_ZMCO GENMASK(1, 0)
+#define REG_ZPOS 0x01
+#define   REG_ZPOS_ZPOS GENMASK(11, 0)
+#define REG_MPOS 0x03
+#define   REG_MPOS_MPOS GENMASK(11, 0)
+#define REG_MANG 0x05
+#define   REG_MANG_MANG GENMASK(11, 0)
+#define REG_CONF 0x07
+#define   REG_CONF_PM   GENMASK(1, 0)
+#define   REG_CONF_HYST GENMASK(3, 2)
+#define   REG_CONF_OUTS GENMASK(5, 4)
+#define   REG_CONF_PWMF GENMASK(7, 6)
+#define   REG_CONF_SF   GENMASK(9, 8)
+#define   REG_CONF_FTH  GENMASK(12, 10)
+#define   REG_CONF_WD   BIT(13)
+#define REG_STATUS 0x0b
+#define   REG_STATUS_MH BIT(3)
+#define   REG_STATUS_ML BIT(4)
+#define   REG_STATUS_MD BIT(5)
+#define REG_RAW_ANGLE 0x0c
+#define   REG_RAW_ANGLE_ANGLE GENMASK(11, 0)
+#define REG_ANGLE 0x0e
+#define   REG_ANGLE_ANGLE GENMASK(11, 0)
+#define REG_AGC 0x1a
+#define   REG_AGC_AGC GENMASK(7, 0)
+#define REG_MAGNITUDE 0x1b
+#define   REG_MAGNITUDE_MAGNITUDE GENMASK(11, 0)
+#define REG_BURN 0xff
+
+/* To simplify some code, the register index and each fields bitmask
+ * are encoded in the address field of the sysfs attributes and
+ * iio_chan_spec. field_get and field_prep are runtime versions of the
+ * FIELD_GET/FIELD_PREP macros.
+ */
+#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
+#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) & (_mask))
+
+#define to_address(reg, field) ((REG_##reg << 16) | REG_##reg##_##field)
+#define reg_from_address(address) (address >> 16)
+#define mask_from_address(address) (address & 0xffff)
+
+struct as5600_priv {
+	struct iio_dev *iio_dev;
+	struct i2c_client *client;
+};
+
+static int as5600_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct as5600_priv *priv = iio_priv(indio_dev);
+	u16 bitmask;
+	s32 angle;
+	u16 reg;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		reg = reg_from_address(chan->address);
+		bitmask = mask_from_address(chan->address);
+		angle = i2c_smbus_read_word_swapped(priv->client, reg);
+		if (angle < 0)
+			return angle;
+		*val = field_get(bitmask, angle);
+
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = 4095;
+
+		return IIO_VAL_INT;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static ssize_t rs5600_attr_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
+	struct as5600_priv *priv = iio_priv(indio_dev);
+	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	unsigned int reg = reg_from_address(this_attr->address);
+	unsigned int mask = mask_from_address(this_attr->address);
+	int ret;
+
+	switch (reg) {
+	case REG_ZMCO:
+	case REG_STATUS:
+	case REG_AGC:
+		ret = i2c_smbus_read_byte_data(priv->client, reg);
+		if (ret < 0)
+			return ret;
+		return sysfs_emit(buf, "%u\n", field_get(mask, ret));
+
+	case REG_ZPOS:
+	case REG_MPOS:
+	case REG_MANG:
+	case REG_CONF:
+	case REG_MAGNITUDE:
+		ret = i2c_smbus_read_word_swapped(priv->client, reg);
+		if (ret < 0)
+			return ret;
+		return sysfs_emit(buf, "%u\n", field_get(mask, ret));
+	}
+
+	return -EINVAL;
+}
+
+static ssize_t rs5600_attr_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t len)
+{
+	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
+	struct as5600_priv *priv = iio_priv(indio_dev);
+	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	unsigned int reg = reg_from_address(this_attr->address);
+	unsigned int mask = mask_from_address(this_attr->address);
+	u16 val_in;
+	u16 out;
+	int ret;
+
+	ret = kstrtou16(buf, 0, &val_in);
+	if (ret)
+		return ret;
+
+	switch (reg) {
+	case REG_ZPOS:
+	case REG_MPOS:
+	case REG_CONF:
+		/* Read then write, as per spec */
+		ret = i2c_smbus_read_word_swapped(priv->client, reg);
+		if (ret < 0)
+			return ret;
+
+		out = ret & ~mask;
+		out |= field_prep(mask, val_in);
+
+		ret = i2c_smbus_write_word_swapped(priv->client, reg, out);
+		if (ret < 0)
+			return ret;
+		break;
+	}
+
+	return len;
+}
+
+#define AS5600_ATTR_RO(name, reg, field)				\
+	IIO_DEVICE_ATTR(name, 0444, rs5600_attr_show, NULL, to_address(reg, field))
+
+#define AS5600_ATTR_RW(name, reg, field)				\
+	IIO_DEVICE_ATTR(name, 0644, rs5600_attr_show, rs5600_attr_store, \
+			to_address(reg, field))
+
+static AS5600_ATTR_RO(zmco, ZMCO, ZMCO);
+static AS5600_ATTR_RO(conf_pm, CONF, PM);
+static AS5600_ATTR_RO(conf_hyst, CONF, HYST);
+static AS5600_ATTR_RO(conf_outs, CONF, OUTS);
+static AS5600_ATTR_RO(conf_pwmf, CONF, PWMF);
+static AS5600_ATTR_RO(conf_sf, CONF, SF);
+static AS5600_ATTR_RO(conf_fth, CONF, FTH);
+static AS5600_ATTR_RO(conf_wd, CONF, WD);
+static AS5600_ATTR_RO(mang, MANG, MANG);
+static AS5600_ATTR_RO(status_mh, STATUS, MH);
+static AS5600_ATTR_RO(status_ml, STATUS, ML);
+static AS5600_ATTR_RO(status_md, STATUS, MD);
+static AS5600_ATTR_RO(agc, AGC, AGC);
+static AS5600_ATTR_RO(magnitude, MAGNITUDE, MAGNITUDE);
+
+static AS5600_ATTR_RW(zpos, ZPOS, ZPOS);
+static AS5600_ATTR_RW(mpos, MPOS, MPOS);
+
+static struct attribute *as5600_attributes[] = {
+	&iio_dev_attr_zmco.dev_attr.attr,
+	&iio_dev_attr_zpos.dev_attr.attr,
+	&iio_dev_attr_mpos.dev_attr.attr,
+	&iio_dev_attr_mang.dev_attr.attr,
+	&iio_dev_attr_conf_pm.dev_attr.attr,
+	&iio_dev_attr_conf_hyst.dev_attr.attr,
+	&iio_dev_attr_conf_outs.dev_attr.attr,
+	&iio_dev_attr_conf_pwmf.dev_attr.attr,
+	&iio_dev_attr_conf_sf.dev_attr.attr,
+	&iio_dev_attr_conf_fth.dev_attr.attr,
+	&iio_dev_attr_conf_wd.dev_attr.attr,
+	&iio_dev_attr_status_mh.dev_attr.attr,
+	&iio_dev_attr_status_ml.dev_attr.attr,
+	&iio_dev_attr_status_md.dev_attr.attr,
+	&iio_dev_attr_agc.dev_attr.attr,
+	&iio_dev_attr_magnitude.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group as5600_attr_group = {
+	.attrs = as5600_attributes,
+};
+
+static const struct iio_chan_spec as5600_channels[] = {
+	{
+		.type = IIO_ANGL,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE),
+		.indexed = 1,
+		.channel = 0,
+		.address = to_address(RAW_ANGLE, ANGLE),
+	},
+	{
+		.type = IIO_ANGL,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE),
+		.indexed = 1,
+		.channel = 1,
+		.address = to_address(ANGLE, ANGLE),
+	},
+};
+
+static const struct iio_info as5600_info = {
+	.read_raw = &as5600_read_raw,
+	.attrs = &as5600_attr_group,
+};
+
+static int as5600_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct as5600_priv *priv;
+	struct iio_dev *indio_dev;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*priv));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	priv = iio_priv(indio_dev);
+	i2c_set_clientdata(client, indio_dev);
+	priv->client = client;
+
+	indio_dev->info = &as5600_info;
+	indio_dev->name = "as5600";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = as5600_channels;
+	indio_dev->num_channels = ARRAY_SIZE(as5600_channels);
+
+	ret = i2c_smbus_read_byte_data(client, REG_STATUS);
+	if (ret < 0)
+		return ret;
+
+	/* No magnet present could be a problem. */
+	if ((ret & REG_STATUS_MD) == 0)
+		dev_warn(&client->dev, "Magnet not detected\n");
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id as5600_i2c_id[] = {
+	{"as5600", 0},
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, as5600_i2c_id);
+
+static struct i2c_driver as5600_driver = {
+	.driver = {
+		.name = "as5600_i2c",
+	},
+	.probe = as5600_probe,
+	.id_table   = as5600_i2c_id,
+};
+
+module_i2c_driver(as5600_driver);
+
+MODULE_AUTHOR("Frank Zago <frank@...o.net>");
+MODULE_DESCRIPTION("ams AS5600 Contactless Potentiometer");
+MODULE_LICENSE("GPL");
--
2.32.0

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