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From:   David Lechner <dlechner@baylibre.com>
To:     linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-staging@lists.linux.dev
Cc:     David Lechner <dlechner@baylibre.com>,
        linux-kernel@vger.kernel.org, Jonathan Cameron <jic23@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Michael Hennerich <Michael.Hennerich@analog.com>,
        =?UTF-8?q?Nuno=20S=C3=A1?= <nuno.sa@analog.com>,
        Axel Haslam <ahaslam@baylibre.com>,
        Philip Molloy <pmolloy@baylibre.com>
Subject: [PATCH 4/4] iio: resolver: add new driver for AD2S1210
Date:   Wed, 20 Sep 2023 12:02:53 -0500
Message-Id: <20230920170253.203395-5-dlechner@baylibre.com>
In-Reply-To: <20230920170253.203395-1-dlechner@baylibre.com>
References: <20230920170253.203395-1-dlechner@baylibre.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

This adds a new driver for Analog Devices, Inc. AD2S1210 resolver to
digital converter. The driver is based on the staging driver with the
following improvements:

Fixes:
- Fix use before initialization bug in probe.
- Fix not checking error returns in probe.
- Remove spi_setup() and spi_set_drvdata() from probe.
- Fix ordering of devm_iio_device_register()
- Remove incorrect hysteresis logic

Changes:
- Use BIT/GENMASK macros.
- Use devicetree to get CLKIN frequency (was sysfs attribute).
- No longer bit-shift the raw value for IIO_CHAN_INFO_RAW.
- Use regmap for register access.
- Remove config sysfs attribute.
- Use gpio array for mode and resolution gpios.
- Invert sample gpio logic and use GPIO_ACTIVE_LOW in devicetree.
- Change hysteresis to use IIO_CHAN_INFO_HYSTERESIS instead of custom
  device attribute.
- Rename fexcit attribute to excitation_frequency.
- Use devicetree to specify resolution instead of sysfs attribute.

Additions:
- Implement IIO_CHAN_INFO_SCALE.
- Implement debugfs register access.
- Add phase_lock_range attribute.
- Add triggered buffer support.

Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 .../testing/sysfs-bus-iio-resolver-ad2s1210   | 109 ++
 drivers/iio/resolver/Kconfig                  |  13 +
 drivers/iio/resolver/Makefile                 |   1 +
 drivers/iio/resolver/ad2s1210.c               | 948 ++++++++++++++++++
 4 files changed, 1071 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-resolver-ad2s1210
 create mode 100644 drivers/iio/resolver/ad2s1210.c

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-resolver-ad2s1210 b/Documentation/ABI/testing/sysfs-bus-iio-resolver-ad2s1210
new file mode 100644
index 000000000000..32890c85168e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-resolver-ad2s1210
@@ -0,0 +1,109 @@
+What:		/sys/bus/iio/devices/iio:deviceX/dos_mis_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Degradation of Signal Mismatch
+		Threshold value. Writing sets the value. Valid values are 0 (0V)
+		to 127 (4.826V). To convert the value to volts, multiply by
+		0.038.
+
+What:		/sys/bus/iio/devices/iio:deviceX/dos_ovr_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Degradation of Signal Overrange
+		Threshold value. Writing sets the value. Valid values are 0 (0V)
+		to 127 (4.826V). To convert the value to volts, multiply by
+		0.038.
+
+What:		/sys/bus/iio/devices/iio:deviceX/dos_rst_max_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Degradation of Signal Reset Maximum
+		Threshold value. Writing sets the value. Valid values are 0 (0V)
+		to 127 (4.826V). To convert the value to volts, multiply by
+		0.038.
+
+What:		/sys/bus/iio/devices/iio:deviceX/dos_rst_min_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Degradation of Signal Reset Minimum
+		Threshold value. Writing sets the value. Valid values are 0 (0V)
+		to 127 (4.826V). To convert the value to volts, multiply by
+		0.038.
+
+What:		/sys/bus/iio/devices/iio:deviceX/fault
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns a hex value containing the fault bit flags.
+
+		Bit	Description
+		---	-----------
+		D7	Sine/cosine inputs clipped
+		D6	Sine/cosine inputs below LOS threshold
+		D5	Sine/cosine inputs exceed DOS overrange threshold
+		D4	Sine/cosine inputs exceed DOS mismatch threshold
+		D3	Tracking error exceeds LOT threshold
+		D2	Velocity exceeds maximum tracking rate
+		D1	Phase error exceeds phase lock range
+		D0	Configuration parity error
+
+		Writing any value will clear any fault conditions.
+
+What:		/sys/bus/iio/devices/iio:deviceX/excitation_frequency
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Excitation Frequency in Hz. Writing
+		sets the Excitation Frequency and performs a software reset on
+		the device to apply the change. Valid values are 2000 (2kHz) to
+		20000 (20kHz).
+
+What:		/sys/bus/iio/devices/iio:deviceX/los_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Loss of Signal Reset Threshold
+		value. Writing sets the value. Valid values are 0 (0V) to
+		127 (4.826V). To convert the value to volts, multiply by 0.038.
+
+What:		/sys/bus/iio/devices/iio:deviceX/lot_high_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Loss of Position Tracking Detection
+		High Threshold value. Writing sets the value. Valid values are
+		0 (0 deg) to 127 (9/18/45 deg). The interpretation of the value
+		depends on the selected resolution. To convert the value to
+		degrees, multiply by 0.35 for 10-bit resolution, multiply by
+		0.14 for 12-bit resolution or multiply by 0.09 for 14 and 16-bit
+		resolution.
+
+What:		/sys/bus/iio/devices/iio:deviceX/lot_low_thrd
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Loss of Position Tracking Detection
+		Low Threshold value. Writing sets the value. Valid values are
+		0 (0 deg) to 127 (9/18/45 deg). The interpretation of the value
+		depends on the selected resolution. To convert the value to
+		degrees, multiply by 0.35 for 10-bit resolution, multiply by
+		0.14 for 12-bit resolution or multiply by 0.09 for 14 and 16-bit
+		resolution.
+
+What:		/sys/bus/iio/devices/iio:deviceX/phase_lock_range
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the current Phase lock range in degrees. Writing
+		sets the value in the configuration register.
+
+What:		/sys/bus/iio/devices/iio:deviceX/phase_lock_range_available
+KernelVersion:  6.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns the possible values for the phase_lock_range
+		attribute, namely 44 and 360.
diff --git a/drivers/iio/resolver/Kconfig b/drivers/iio/resolver/Kconfig
index 47dbfead9b31..424529d36080 100644
--- a/drivers/iio/resolver/Kconfig
+++ b/drivers/iio/resolver/Kconfig
@@ -25,4 +25,17 @@ config AD2S1200
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad2s1200.
+
+config AD2S1210
+	tristate "Analog Devices ad2s1210 driver"
+	depends on SPI
+	depends on COMMON_CLK
+	depends on GPIOLIB || COMPILE_TEST
+	help
+	  Say yes here to build support for Analog Devices spi resolver
+	  to digital converters, ad2s1210, provides direct access via sysfs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ad2s1210.
+
 endmenu
diff --git a/drivers/iio/resolver/Makefile b/drivers/iio/resolver/Makefile
index fa558138ce45..7f6c876c35ae 100644
--- a/drivers/iio/resolver/Makefile
+++ b/drivers/iio/resolver/Makefile
@@ -5,3 +5,4 @@
 
 obj-$(CONFIG_AD2S90) += ad2s90.o
 obj-$(CONFIG_AD2S1200) += ad2s1200.o
+obj-$(CONFIG_AD2S1210) += ad2s1210.o
diff --git a/drivers/iio/resolver/ad2s1210.c b/drivers/iio/resolver/ad2s1210.c
new file mode 100644
index 000000000000..97833fbcbf7a
--- /dev/null
+++ b/drivers/iio/resolver/ad2s1210.c
@@ -0,0 +1,948 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ad2s1210.c support for the ADI Resolver to Digital Converters: AD2S1210
+ *
+ * Copyright (c) 2010-2010 Analog Devices Inc.
+ * Copyright (C) 2023 BayLibre, SAS
+ */
+
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/spi/spi.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/iio/trigger_consumer.h>
+#include <linux/iio/triggered_buffer.h>
+
+#define DRV_NAME "ad2s1210"
+
+/* default value of control register on powerup */
+#define AD2S1210_DEF_CONTROL		0x7E
+
+/* control register flags */
+#define AD2S1210_ADDRESS_DATA		BIT(7)
+#define AD2S1210_PHASE_LOCK_RANGE_44	BIT(5)
+#define AD2S1210_ENABLE_HYSTERESIS	BIT(4)
+#define AD2S1210_SET_ENRES		GENMASK(3, 2)
+#define AD2S1210_SET_RES		GENMASK(1, 0)
+
+#define AD2S1210_REG_POSITION_MSB	0x80
+#define AD2S1210_REG_POSITION_LSB	0x81
+#define AD2S1210_REG_VELOCITY_MSB	0x82
+#define AD2S1210_REG_VELOCITY_LSB	0x83
+#define AD2S1210_REG_LOS_THRD		0x88
+#define AD2S1210_REG_DOS_OVR_THRD	0x89
+#define AD2S1210_REG_DOS_MIS_THRD	0x8A
+#define AD2S1210_REG_DOS_RST_MAX_THRD	0x8B
+#define AD2S1210_REG_DOS_RST_MIN_THRD	0x8C
+#define AD2S1210_REG_LOT_HIGH_THRD	0x8D
+#define AD2S1210_REG_LOT_LOW_THRD	0x8E
+#define AD2S1210_REG_EXCIT_FREQ		0x91
+#define AD2S1210_REG_CONTROL		0x92
+#define AD2S1210_REG_SOFT_RESET		0xF0
+#define AD2S1210_REG_FAULT		0xFF
+
+#define AD2S1210_MIN_CLKIN	6144000
+#define AD2S1210_MAX_CLKIN	10240000
+#define AD2S1210_MIN_EXCIT	2000
+#define AD2S1210_DEF_EXCIT	10000
+#define AD2S1210_MAX_EXCIT	20000
+#define AD2S1210_MIN_FCW	0x4
+#define AD2S1210_MAX_FCW	0x50
+
+enum ad2s1210_mode {
+	AD2S1210_MODE_POS = 0b00,
+	AD2S1210_MODE_VEL = 0b01,
+	AD2S1210_MODE_CONFIG = 0b11,
+};
+
+enum ad2s1210_resolution {
+	AD2S1210_RES_10 = 0b00,
+	AD2S1210_RES_12 = 0b01,
+	AD2S1210_RES_14 = 0b10,
+	AD2S1210_RES_16 = 0b11,
+};
+
+struct ad2s1210_state {
+	struct mutex lock;
+	struct spi_device *sdev;
+	/** GPIO pin connected to SAMPLE line. */
+	struct gpio_desc *sample_gpio;
+	/** GPIO pins connected to A0 and A1 lines. */
+	struct gpio_descs *mode_gpios;
+	/** Used to access config registers. */
+	struct regmap *regmap;
+	/** The external oscillator frequency in Hz. */
+	unsigned long fclkin;
+	/** The selected resolution */
+	enum ad2s1210_resolution resolution;
+	/* Scan buffer */
+	struct {
+		__be16 chan[2];
+		/* Ensure timestamp is naturally aligned. */
+		s64 timestamp __aligned(8);
+	} scan;
+	u8 rx[2] __aligned(IIO_DMA_MINALIGN);
+	u8 tx[2];
+};
+
+static int ad2s1210_set_mode(struct ad2s1210_state *st, enum ad2s1210_mode mode)
+{
+	struct gpio_descs *gpios = st->mode_gpios;
+	DECLARE_BITMAP(bitmap, 2);
+
+	bitmap[0] = mode;
+
+	return gpiod_set_array_value(gpios->ndescs, gpios->desc, gpios->info,
+				     bitmap);
+}
+
+/**
+ * Writes the given data to the given register address.
+ *
+ * If the mode is configurable, the device will first be placed in
+ * configuration mode.
+ */
+static int ad2s1210_regmap_reg_write(void *context, unsigned int reg,
+				     unsigned int val)
+{
+	struct ad2s1210_state *st = context;
+	struct spi_transfer xfers[] = {
+		{
+			.len = 1,
+			.rx_buf = &st->rx[0],
+			.tx_buf = &st->tx[0],
+			.cs_change = 1,
+		}, {
+			.len = 1,
+			.rx_buf = &st->rx[1],
+			.tx_buf = &st->tx[1],
+		},
+	};
+	int ret;
+
+	/* values can only be 7 bits, the MSB indicates an address */
+	if (val & ~0x7F)
+		return -EINVAL;
+
+	st->tx[0] = reg;
+	st->tx[1] = val;
+
+	ret = ad2s1210_set_mode(st, AD2S1210_MODE_CONFIG);
+	if (ret < 0)
+		return ret;
+
+	return spi_sync_transfer(st->sdev, xfers, ARRAY_SIZE(xfers));
+}
+
+/**
+ * Reads value from one of the registers.
+ *
+ * If the mode is configurable, the device will first be placed in
+ * configuration mode.
+ */
+static int ad2s1210_regmap_reg_read(void *context, unsigned int reg,
+				    unsigned int *val)
+{
+	struct ad2s1210_state *st = context;
+	struct spi_transfer xfers[] = {
+		{
+			.len = 1,
+			.rx_buf = &st->rx[0],
+			.tx_buf = &st->tx[0],
+			.cs_change = 1,
+		}, {
+			.len = 1,
+			.rx_buf = &st->rx[1],
+			.tx_buf = &st->tx[1],
+		},
+	};
+	int ret;
+
+	ret = ad2s1210_set_mode(st, AD2S1210_MODE_CONFIG);
+	if (ret < 0)
+		return ret;
+
+	st->tx[0] = reg;
+	/* Must be valid register address here otherwise this could write data.
+	 * It doesn't matter which one.
+	 */
+	st->tx[1] = AD2S1210_REG_FAULT;
+
+	ret = spi_sync_transfer(st->sdev, xfers, ARRAY_SIZE(xfers));
+	if (ret < 0)
+		return ret;
+
+	/* If the D7 bit is set on any read/write register, it indicates a
+	 * parity error. The fault register is read-only and the D7 bit means
+	 * something else there.
+	 */
+	if (reg != AD2S1210_REG_FAULT && st->rx[1] & AD2S1210_ADDRESS_DATA)
+		return -EBADMSG;
+
+	*val = st->rx[1];
+
+	return 0;
+}
+
+/**
+ * Sets the excitation frequency and performs software reset.
+ *
+ * Must be called with lock held.
+ */
+static int ad2s1210_set_excitation_frequency(struct ad2s1210_state *st,
+					     u16 fexcit)
+{
+	int ret;
+	u8 fcw;
+
+	fcw = fexcit * (1 << 15) / st->fclkin;
+	if (fcw < AD2S1210_MIN_FCW || fcw > AD2S1210_MAX_FCW)
+		return -ERANGE;
+
+	ret = regmap_write(st->regmap, AD2S1210_REG_EXCIT_FREQ, fcw);
+	if (ret < 0)
+		return ret;
+
+	/* software reset reinitializes the excitation frequency output */
+	return regmap_write(st->regmap, AD2S1210_REG_SOFT_RESET, 0);
+}
+
+static ssize_t excitation_frequency_show(struct device *dev,
+						  struct device_attribute *attr,
+						  char *buf)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	unsigned int value;
+	u16 fexcit;
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_read(st->regmap, AD2S1210_REG_EXCIT_FREQ, &value);
+	if (ret < 0)
+		goto error_ret;
+
+	fexcit = value * st->fclkin / (1 << 15);
+
+	ret = sysfs_emit(buf, "%u\n", fexcit);
+
+error_ret:
+	mutex_unlock(&st->lock);
+	return ret;
+}
+
+static ssize_t excitation_frequency_store(struct device *dev,
+						   struct device_attribute *attr,
+						   const char *buf, size_t len)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	u16 fexcit;
+	int ret;
+
+	ret = kstrtou16(buf, 10, &fexcit);
+	if (ret < 0 || fexcit < AD2S1210_MIN_EXCIT || fexcit > AD2S1210_MAX_EXCIT)
+		return -EINVAL;
+
+	mutex_lock(&st->lock);
+	ret = ad2s1210_set_excitation_frequency(st, fexcit);
+	if (ret < 0)
+		goto error_ret;
+
+	ret = len;
+
+error_ret:
+	mutex_unlock(&st->lock);
+
+	return ret;
+}
+
+static ssize_t phase_lock_range_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_test_bits(st->regmap, AD2S1210_REG_CONTROL,
+			       AD2S1210_PHASE_LOCK_RANGE_44);
+	if (ret < 0)
+		goto error_ret;
+
+	ret = sysfs_emit(buf, "%d\n", ret ? 44 : 360);
+
+error_ret:
+	mutex_unlock(&st->lock);
+	return ret;
+}
+
+static ssize_t phase_lock_range_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t len)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	u16 udata;
+	int ret;
+
+	ret = kstrtou16(buf, 10, &udata);
+	if (ret < 0 || (udata != 44 && udata != 360))
+		return -EINVAL;
+
+	mutex_lock(&st->lock);
+
+	ret = regmap_update_bits(st->regmap, AD2S1210_REG_CONTROL,
+				 AD2S1210_PHASE_LOCK_RANGE_44,
+				 udata == 44 ? AD2S1210_PHASE_LOCK_RANGE_44 : 0);
+	if (ret < 0)
+		goto error_ret;
+
+	ret = len;
+
+error_ret:
+	mutex_unlock(&st->lock);
+	return ret;
+}
+
+static ssize_t phase_lock_range_available_show(struct device *dev,
+					       struct device_attribute *attr,
+					       char *buf)
+{
+	return sysfs_emit(buf, "44 360\n");
+}
+
+/* read the fault register since last sample */
+static ssize_t fault_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	unsigned int value;
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &value);
+	mutex_unlock(&st->lock);
+
+	return ret < 0 ? ret : sysfs_emit(buf, "0x%02x\n", value);
+}
+
+static ssize_t fault_store(struct device *dev,
+			   struct device_attribute *attr,
+			   const char *buf,
+			   size_t len)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	unsigned int value;
+	int ret;
+
+	mutex_lock(&st->lock);
+
+	gpiod_set_value(st->sample_gpio, 1);
+	/* delay (2 * tck + 20) nano seconds */
+	udelay(1);
+	gpiod_set_value(st->sample_gpio, 0);
+
+	ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &value);
+	if (ret < 0)
+		goto error_ret;
+
+	gpiod_set_value(st->sample_gpio, 1);
+	gpiod_set_value(st->sample_gpio, 0);
+
+error_ret:
+	mutex_unlock(&st->lock);
+
+	return ret < 0 ? ret : len;
+}
+
+static ssize_t reg_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	struct iio_dev_attr *iattr = to_iio_dev_attr(attr);
+	unsigned int value;
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_read(st->regmap, iattr->address, &value);
+	mutex_unlock(&st->lock);
+
+	return ret < 0 ? ret : sysfs_emit(buf, "%d\n", value);
+}
+
+static ssize_t reg_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
+	unsigned char data;
+	int ret;
+	struct iio_dev_attr *iattr = to_iio_dev_attr(attr);
+
+	ret = kstrtou8(buf, 10, &data);
+	if (ret < 0)
+		return -EINVAL;
+
+	mutex_lock(&st->lock);
+	ret = regmap_write(st->regmap, iattr->address, data);
+	mutex_unlock(&st->lock);
+	return ret < 0 ? ret : len;
+}
+
+static const int ad2s1210_velocity_scale[] = {
+	17089132, /* 8.192MHz / (2*pi * 2500 / 2^15) */
+	42722830, /* 8.192MHz / (2*pi * 1000 / 2^15) */
+	85445659, /* 8.192MHz / (2*pi * 500 / 2^15) */
+	341782638, /* 8.192MHz / (2*pi * 125 / 2^15) */
+};
+
+static int ad2s1210_read_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int *val,
+			     int *val2,
+			     long mask)
+{
+	struct ad2s1210_state *st = iio_priv(indio_dev);
+	int ret = 0;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&st->lock);
+		gpiod_set_value(st->sample_gpio, 1);
+		/* delay (6 * tck + 20) nano seconds */
+		udelay(1);
+
+		switch (chan->type) {
+		case IIO_ANGL:
+			ret = ad2s1210_set_mode(st, AD2S1210_MODE_POS);
+			break;
+		case IIO_ANGL_VEL:
+			ret = ad2s1210_set_mode(st, AD2S1210_MODE_VEL);
+			break;
+		default:
+			ret = -EINVAL;
+			break;
+		}
+		if (ret < 0)
+			goto error_info_raw;
+		ret = spi_read(st->sdev, st->rx, 2);
+		if (ret < 0)
+			goto error_info_raw;
+
+		switch (chan->type) {
+		case IIO_ANGL:
+			*val = be16_to_cpup((__be16 *)st->rx);
+			ret = IIO_VAL_INT;
+			break;
+		case IIO_ANGL_VEL:
+			*val = (s16)be16_to_cpup((__be16 *)st->rx);
+			ret = IIO_VAL_INT;
+			break;
+		default:
+			ret = -EINVAL;
+			break;
+		}
+
+error_info_raw:
+		gpiod_set_value(st->sample_gpio, 0);
+		/* delay (2 * tck + 20) nano seconds */
+		udelay(1);
+		mutex_unlock(&st->lock);
+		break;
+
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_ANGL:
+			/* approx 0.3 arc min converted to radians */
+			*val = 0;
+			*val2 = 95874;
+			ret = IIO_VAL_INT_PLUS_NANO;
+			break;
+		case IIO_ANGL_VEL:
+			*val = st->fclkin;
+			*val2 = ad2s1210_velocity_scale[st->resolution];
+			ret = IIO_VAL_FRACTIONAL;
+			break;
+		default:
+			ret = -EINVAL;
+			break;
+		}
+		break;
+
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			mutex_lock(&st->lock);
+			ret = regmap_test_bits(st->regmap, AD2S1210_REG_CONTROL,
+					       AD2S1210_ENABLE_HYSTERESIS);
+			if (ret < 0)
+				goto error_info_hysteresis;
+
+			*val = !!ret;
+			ret = IIO_VAL_INT;
+
+error_info_hysteresis:
+			mutex_unlock(&st->lock);
+			break;
+		default:
+			ret = -EINVAL;
+			break;
+		}
+		break;
+
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+static int ad2s1210_read_avail(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       const int **vals, int *type,
+			       int *length, long mask)
+{
+	static const int available[] = { 0, 1 };
+	int ret = -EINVAL;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			*vals = available;
+			*type = IIO_VAL_INT;
+			*length = ARRAY_SIZE(available);
+			ret = IIO_AVAIL_LIST;
+			break;
+		default:
+			break;
+		}
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static int ad2s1210_write_raw(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan,
+			      int val, int val2, long mask)
+{
+	struct ad2s1210_state *st = iio_priv(indio_dev);
+	int ret = -EINVAL;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			mutex_lock(&st->lock);
+			ret = regmap_update_bits(st->regmap, AD2S1210_REG_CONTROL,
+						 AD2S1210_ENABLE_HYSTERESIS,
+						 val ? AD2S1210_ENABLE_HYSTERESIS
+						     : 0);
+			mutex_unlock(&st->lock);
+			break;
+
+		default:
+			break;
+		}
+		break;
+
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static IIO_DEVICE_ATTR_RW(excitation_frequency, 0);
+static IIO_DEVICE_ATTR_RW(phase_lock_range, 0);
+static IIO_DEVICE_ATTR_RO(phase_lock_range_available, 0);
+static IIO_DEVICE_ATTR_RW(fault, 0);
+static IIO_DEVICE_ATTR_NAMED_RW(los_thrd, reg, AD2S1210_REG_LOS_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(dos_ovr_thrd, reg, AD2S1210_REG_DOS_OVR_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(dos_mis_thrd, reg, AD2S1210_REG_DOS_MIS_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(dos_rst_max_thrd, reg,
+				AD2S1210_REG_DOS_RST_MAX_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(dos_rst_min_thrd, reg,
+				AD2S1210_REG_DOS_RST_MIN_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(lot_high_thrd, reg, AD2S1210_REG_LOT_HIGH_THRD);
+static IIO_DEVICE_ATTR_NAMED_RW(lot_low_thrd, reg, AD2S1210_REG_LOT_LOW_THRD);
+
+static const struct iio_chan_spec ad2s1210_channels[] = {
+	{
+		.type = IIO_ANGL,
+		.indexed = 1,
+		.channel = 0,
+		.scan_index = 0,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 16,
+			.storagebits = 16,
+			.endianness = IIO_BE,
+		},
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE) |
+				      BIT(IIO_CHAN_INFO_HYSTERESIS),
+		.info_mask_separate_available =
+					BIT(IIO_CHAN_INFO_HYSTERESIS),
+		.datasheet_name = "position",
+	}, {
+		.type = IIO_ANGL_VEL,
+		.indexed = 1,
+		.channel = 0,
+		.scan_index = 1,
+		.scan_type = {
+			.sign = 's',
+			.realbits = 16,
+			.storagebits = 16,
+			.endianness = IIO_BE,
+		},
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.datasheet_name = "velocity",
+	},
+	IIO_CHAN_SOFT_TIMESTAMP(2),
+};
+
+static struct attribute *ad2s1210_attributes[] = {
+	&iio_dev_attr_excitation_frequency.dev_attr.attr,
+	&iio_dev_attr_phase_lock_range.dev_attr.attr,
+	&iio_dev_attr_phase_lock_range_available.dev_attr.attr,
+	&iio_dev_attr_fault.dev_attr.attr,
+	&iio_dev_attr_los_thrd.dev_attr.attr,
+	&iio_dev_attr_dos_ovr_thrd.dev_attr.attr,
+	&iio_dev_attr_dos_mis_thrd.dev_attr.attr,
+	&iio_dev_attr_dos_rst_max_thrd.dev_attr.attr,
+	&iio_dev_attr_dos_rst_min_thrd.dev_attr.attr,
+	&iio_dev_attr_lot_high_thrd.dev_attr.attr,
+	&iio_dev_attr_lot_low_thrd.dev_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group ad2s1210_attribute_group = {
+	.attrs = ad2s1210_attributes,
+};
+
+static int ad2s1210_debugfs_reg_access(struct iio_dev *indio_dev,
+				       unsigned int reg, unsigned int writeval,
+				       unsigned int *readval)
+{
+	struct ad2s1210_state *st = iio_priv(indio_dev);
+	int ret;
+
+	mutex_lock(&st->lock);
+
+	if (readval)
+		ret = regmap_read(st->regmap, reg, readval);
+	else
+		ret = regmap_write(st->regmap, reg, writeval);
+
+	mutex_unlock(&st->lock);
+
+	return ret;
+}
+
+static irqreturn_t ad2s1210_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct ad2s1210_state *st = iio_priv(indio_dev);
+	size_t chan = 0;
+	int ret;
+
+	mutex_lock(&st->lock);
+
+	memset(&st->scan, 0, sizeof(st->scan));
+	gpiod_set_value(st->sample_gpio, 1);
+
+	if (test_bit(0, indio_dev->active_scan_mask)) {
+		ret = ad2s1210_set_mode(st, AD2S1210_MODE_POS);
+		if (ret < 0)
+			goto error_ret;
+
+		/* REVIST: we can read 3 bytes here and also get fault flags */
+		ret = spi_read(st->sdev, st->rx, 2);
+		if (ret < 0)
+			goto error_ret;
+
+		memcpy(&st->scan.chan[chan++], st->rx, 2);
+	}
+
+	if (test_bit(1, indio_dev->active_scan_mask)) {
+		ret = ad2s1210_set_mode(st, AD2S1210_MODE_VEL);
+		if (ret < 0)
+			goto error_ret;
+
+		/* REVIST: we can read 3 bytes here and also get fault flags */
+		ret = spi_read(st->sdev, st->rx, 2);
+		if (ret < 0)
+			goto error_ret;
+
+		memcpy(&st->scan.chan[chan++], st->rx, 2);
+	}
+
+	iio_push_to_buffers_with_timestamp(indio_dev, &st->scan, pf->timestamp);
+
+error_ret:
+	gpiod_set_value(st->sample_gpio, 0);
+	mutex_unlock(&st->lock);
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
+static const struct iio_info ad2s1210_info = {
+	.read_raw = ad2s1210_read_raw,
+	.read_avail = ad2s1210_read_avail,
+	.write_raw = ad2s1210_write_raw,
+	.attrs = &ad2s1210_attribute_group,
+	.debugfs_reg_access = &ad2s1210_debugfs_reg_access,
+};
+
+static int ad2s1210_setup_properties(struct ad2s1210_state *st)
+{
+	struct device *dev = &st->sdev->dev;
+	u32 val;
+	int ret;
+
+	ret = device_property_read_u32(dev, "assigned-resolution-bits", &val);
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+			"failed to read assigned-resolution-bits property\n");
+
+	if (val < 10 || val > 16)
+		return dev_err_probe(dev, -EINVAL,
+				     "resolution out of range: %u\n", val);
+
+	st->resolution = (val - 10) >> 1;
+
+	return 0;
+}
+
+static int ad2s1210_setup_clocks(struct ad2s1210_state *st)
+{
+	struct device *dev = &st->sdev->dev;
+	struct clk *clk;
+
+	clk = devm_clk_get_enabled(dev, NULL);
+	if (IS_ERR(clk))
+		return dev_err_probe(dev, PTR_ERR(clk), "failed to get clock\n");
+
+	st->fclkin = clk_get_rate(clk);
+	if (st->fclkin < AD2S1210_MIN_CLKIN || st->fclkin > AD2S1210_MAX_CLKIN)
+		return dev_err_probe(dev, -EINVAL,
+				     "clock frequency out of range: %lu\n",
+				     st->fclkin);
+
+	return 0;
+}
+
+static int ad2s1210_setup_gpios(struct ad2s1210_state *st)
+{
+	struct device *dev = &st->sdev->dev;
+	struct gpio_descs *resolution_gpios;
+	DECLARE_BITMAP(bitmap, 2);
+	int ret;
+
+	/* should not be sampling on startup */
+	st->sample_gpio = devm_gpiod_get(dev, "sample", GPIOD_OUT_LOW);
+	if (IS_ERR(st->sample_gpio))
+		return dev_err_probe(dev, PTR_ERR(st->sample_gpio),
+				     "failed to request sample GPIO\n");
+
+	/* both pins high means that we start in config mode */
+	st->mode_gpios = devm_gpiod_get_array(dev, "mode", GPIOD_OUT_HIGH);
+	if (IS_ERR(st->mode_gpios))
+		return dev_err_probe(dev, PTR_ERR(st->mode_gpios),
+				     "failed to request mode GPIOs\n");
+
+	if (st->mode_gpios->ndescs != 2)
+		return dev_err_probe(dev, -EINVAL,
+				     "requires exactly 2 mode-gpios\n");
+
+	/* If resolution gpios are provided, they get set to the required
+	 * resolution, otherwise it is assumed the RES0 and RES1 pins are
+	 * hard-wired to match the resolution indicated in the devicetree.
+	 */
+	resolution_gpios = devm_gpiod_get_array_optional(dev, "resolution",
+							 GPIOD_ASIS);
+	if (IS_ERR(resolution_gpios))
+		return dev_err_probe(dev, PTR_ERR(resolution_gpios),
+				     "failed to request resolution GPIOs\n");
+
+	if (resolution_gpios) {
+		if (resolution_gpios->ndescs != 2)
+			return dev_err_probe(dev, -EINVAL,
+				      "requires exactly 2 resolution-gpios\n");
+
+		bitmap[0] = st->resolution;
+
+		ret = gpiod_set_array_value(resolution_gpios->ndescs,
+					    resolution_gpios->desc,
+					    resolution_gpios->info,
+					    bitmap);
+		if (ret < 0)
+			return dev_err_probe(dev, ret,
+					     "failed to set resolution gpios\n");
+	}
+
+	return 0;
+}
+
+static const struct regmap_range ad2s1210_regmap_readable_ranges[] = {
+	regmap_reg_range(AD2S1210_REG_POSITION_MSB, AD2S1210_REG_VELOCITY_LSB),
+	regmap_reg_range(AD2S1210_REG_LOS_THRD, AD2S1210_REG_LOT_LOW_THRD),
+	regmap_reg_range(AD2S1210_REG_EXCIT_FREQ, AD2S1210_REG_CONTROL),
+	regmap_reg_range(AD2S1210_REG_FAULT, AD2S1210_REG_FAULT),
+};
+
+static const struct regmap_access_table ad2s1210_regmap_rd_table = {
+	.yes_ranges = ad2s1210_regmap_readable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(ad2s1210_regmap_readable_ranges),
+};
+
+static const struct regmap_range ad2s1210_regmap_writeable_ranges[] = {
+	regmap_reg_range(AD2S1210_REG_LOS_THRD, AD2S1210_REG_LOT_LOW_THRD),
+	regmap_reg_range(AD2S1210_REG_EXCIT_FREQ, AD2S1210_REG_CONTROL),
+	regmap_reg_range(AD2S1210_REG_SOFT_RESET, AD2S1210_REG_SOFT_RESET),
+	regmap_reg_range(AD2S1210_REG_FAULT, AD2S1210_REG_FAULT),
+};
+
+static const struct regmap_access_table ad2s1210_regmap_wr_table = {
+	.yes_ranges = ad2s1210_regmap_writeable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(ad2s1210_regmap_writeable_ranges),
+};
+
+static int ad2s1210_setup_regmap(struct ad2s1210_state *st)
+{
+	struct device *dev = &st->sdev->dev;
+	const struct regmap_config config = {
+		.reg_bits = 8,
+		.val_bits = 8,
+		.disable_locking = true,
+		.reg_read = ad2s1210_regmap_reg_read,
+		.reg_write = ad2s1210_regmap_reg_write,
+		.rd_table = &ad2s1210_regmap_rd_table,
+		.wr_table = &ad2s1210_regmap_wr_table,
+		.can_sleep = true,
+	};
+
+	st->regmap = devm_regmap_init(dev, NULL, st, &config);
+	if (IS_ERR(st->regmap))
+		return dev_err_probe(dev, PTR_ERR(st->regmap),
+				     "failed to allocate register map\n");
+
+	return 0;
+}
+
+static int ad2s1210_init(struct ad2s1210_state *st)
+{
+	unsigned char data;
+	int ret;
+
+	mutex_lock(&st->lock);
+
+	data = AD2S1210_DEF_CONTROL & ~AD2S1210_SET_RES;
+	data |= st->resolution;
+
+	ret = regmap_write(st->regmap, AD2S1210_REG_CONTROL, data);
+	if (ret < 0)
+		goto error_ret;
+
+	ret = ad2s1210_set_excitation_frequency(st, AD2S1210_DEF_EXCIT);
+
+error_ret:
+	mutex_unlock(&st->lock);
+	return ret;
+}
+
+static int ad2s1210_probe(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev;
+	struct ad2s1210_state *st;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+
+	mutex_init(&st->lock);
+	st->sdev = spi;
+
+	ret = ad2s1210_setup_properties(st);
+	if (ret < 0)
+		return ret;
+
+	ret = ad2s1210_setup_clocks(st);
+	if (ret < 0)
+		return ret;
+
+	ret = ad2s1210_setup_gpios(st);
+	if (ret < 0)
+		return ret;
+
+	ret = ad2s1210_setup_regmap(st);
+	if (ret < 0)
+		return ret;
+
+	ret = ad2s1210_init(st);
+	if (ret < 0)
+		return ret;
+
+	indio_dev->info = &ad2s1210_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = ad2s1210_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ad2s1210_channels);
+	indio_dev->name = spi_get_device_id(spi)->name;
+
+	ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
+					      &iio_pollfunc_store_time,
+					      &ad2s1210_trigger_handler, NULL);
+	if (ret < 0)
+		return dev_err_probe(&spi->dev, ret,
+				     "iio triggered buffer setup failed\n");
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static const struct of_device_id ad2s1210_of_match[] = {
+	{ .compatible = "adi,ad2s1210", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ad2s1210_of_match);
+
+static const struct spi_device_id ad2s1210_id[] = {
+	{ "ad2s1210" },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, ad2s1210_id);
+
+static struct spi_driver ad2s1210_driver = {
+	.driver = {
+		.name = DRV_NAME,
+		.of_match_table = ad2s1210_of_match,
+	},
+	.probe = ad2s1210_probe,
+	.id_table = ad2s1210_id,
+};
+module_spi_driver(ad2s1210_driver);
+
+MODULE_AUTHOR("Graff Yang <graff.yang@gmail.com>");
+MODULE_DESCRIPTION("Analog Devices AD2S1210 Resolver to Digital SPI driver");
+MODULE_LICENSE("GPL v2");
-- 
2.34.1