[PATCH v2 7/7] iio: adc: ad4170: Add support for weigh scale and RTD sensors

[Marcelo Schmitt <marcelo.schmitt@analog.com>]

The AD4170 design has features to aid interfacing with weigh scale and RTD
sensors that are expected to be setup with external circuitry for proper
sensor operation. A key characteristic of those sensors is that the circuit
they are in must be excited with a pair of signals. The external circuit
can be excited either by voltage supply or by AD4170 excitation signals.
The sensor can then be read through a different pair of lines that are
connected to AD4170 ADC.

Configure AD4170 to handle external circuit sensors.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
changes since v1:
- Improved to support more than one external sensor connected.

 drivers/iio/adc/ad4170.c | 375 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 372 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ad4170.c b/drivers/iio/adc/ad4170.c
index 335b4194c7eb..9e4a9b524dd4 100644
--- a/drivers/iio/adc/ad4170.c
+++ b/drivers/iio/adc/ad4170.c
@@ -62,6 +62,8 @@
 #define AD4170_FILTER_FS_REG(x)				(0xC7 + 14 * (x))
 #define AD4170_OFFSET_REG(x)				(0xCA + 14 * (x))
 #define AD4170_GAIN_REG(x)				(0xCD + 14 * (x))
+#define AD4170_V_BIAS_REG				0x135
+#define AD4170_CURRENT_SRC_REG(x)			(0x139 + 2 * (x))
 #define AD4170_GPIO_MODE_REG				0x191
 #define AD4170_GPIO_OUTPUT_REG				0x193
 #define AD4170_GPIO_INPUT_REG				0x195
@@ -110,6 +112,10 @@
 /* AD4170_FILTER_REG */
 #define AD4170_FILTER_FILTER_TYPE_MSK			GENMASK(3, 0)
 
+/* AD4170_CURRENT_SRC_REG */
+#define AD4170_CURRENT_SRC_I_OUT_PIN_MSK		GENMASK(12, 8)
+#define AD4170_CURRENT_SRC_I_OUT_VAL_MSK		GENMASK(2, 0)
+
 /* AD4170 register constants */
 
 /* AD4170_CLOCK_CTRL_REG constants */
@@ -171,6 +177,21 @@
 #define AD4170_FILTER_FILTER_TYPE_SINC5			0x4
 #define AD4170_FILTER_FILTER_TYPE_SINC3			0x6
 
+/* AD4170_CURRENT_SRC_REG constants */
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN0		0
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN1		1
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN2		2
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN3		3
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN4		4
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN5		5
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN6		6
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN7		7
+#define AD4170_CURRENT_SRC_I_OUT_PIN_AIN8		8
+#define AD4170_CURRENT_SRC_I_OUT_PIN_GPIO0		17
+#define AD4170_CURRENT_SRC_I_OUT_PIN_GPIO1		18
+#define AD4170_CURRENT_SRC_I_OUT_PIN_GPIO2		19
+#define AD4170_CURRENT_SRC_I_OUT_PIN_GPIO3		20
+
 /* Device properties and auxiliary constants */
 
 #define AD4170_NUM_ANALOG_PINS				9
@@ -204,6 +225,15 @@
 #define AD4170_PIN_UNASIGNED				0x00
 #define AD4170_PIN_ANALOG_IN				0x01
 #define AD4170_PIN_CURRENT_OUT				0x02
+#define AD4170_PIN_VBIAS				0x04
+
+/* GPIO pin functions  */
+#define AD4170_GPIO_UNASIGNED				0x00
+#define AD4170_GPIO_AC_EXCITATION			0x02
+#define AD4170_GPIO_OUTPUT				0x04
+
+/* Current source */
+#define AD4170_CURRENT_SRC_DISABLED			0xFF
 
 static const unsigned int ad4170_reg_size[] = {
 	[AD4170_CONFIG_A_REG] = 1,
@@ -244,6 +274,8 @@ static const unsigned int ad4170_reg_size[] = {
 	[AD4170_OFFSET_REG(5) ... AD4170_GAIN_REG(5)] = 3,
 	[AD4170_OFFSET_REG(6) ... AD4170_GAIN_REG(6)] = 3,
 	[AD4170_OFFSET_REG(7) ... AD4170_GAIN_REG(7)] = 3,
+	[AD4170_V_BIAS_REG] = 2,
+	[AD4170_CURRENT_SRC_REG(0) ... AD4170_CURRENT_SRC_REG(3)] = 2,
 	[AD4170_GPIO_MODE_REG] = 2,
 	[AD4170_GPIO_OUTPUT_REG] = 2,
 	[AD4170_GPIO_INPUT_REG] = 2,
@@ -305,6 +337,33 @@ static const unsigned int ad4170_sinc5_filt_fs_tbl[] = {
 	1, 2, 4, 8, 12, 16, 20, 40, 48, 80, 100, 256,
 };
 
+static const unsigned int ad4170_iout_pin_tbl[] = {
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN0,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN1,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN2,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN3,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN4,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN5,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN6,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN7,
+	AD4170_CURRENT_SRC_I_OUT_PIN_AIN8,
+	AD4170_CURRENT_SRC_I_OUT_PIN_GPIO0,
+	AD4170_CURRENT_SRC_I_OUT_PIN_GPIO1,
+	AD4170_CURRENT_SRC_I_OUT_PIN_GPIO2,
+	AD4170_CURRENT_SRC_I_OUT_PIN_GPIO3,
+};
+
+static const unsigned int ad4170_iout_current_ua_tbl[] = {
+	0, 10, 50, 100, 250, 500, 1000, 1500
+};
+
+enum ad4170_sensor_type {
+	AD4170_WEIGH_SCALE_SENSOR = 0,
+	AD4170_RTD_SENSOR = 1,
+	AD4170_THERMOCOUPLE_SENSOR = 2,
+	AD4170_ADC_SENSOR = 3,
+};
+
 struct ad4170_chip_info {
 	const char *name;
 };
@@ -378,6 +437,8 @@ struct ad4170_state {
 	struct clk *ext_clk;
 	struct clk_hw int_clk_hw;
 	int pins_fn[AD4170_NUM_ANALOG_PINS];
+	int gpio_fn[AD4170_NUM_GPIO_PINS];
+	unsigned int cur_src_pins[AD4170_NUM_CURRENT_SRC];
 	struct gpio_chip gpiochip;
 	u32 int_pin_sel;
 	int sps_tbl[ARRAY_SIZE(ad4170_filt_names)][AD4170_MAX_FS_TBL_SIZE][2];
@@ -925,6 +986,19 @@ static int ad4170_get_ain_voltage_uv(struct ad4170_state *st, int ain_n,
 	struct device *dev = &st->spi->dev;
 
 	*ain_voltage = 0;
+	/*
+	 * The voltage bias (vbias) sets the common-mode voltage of the channel
+	 * to (AVDD + AVSS)/2. If provided, AVSS supply provides the magnitude
+	 * (absolute value) of the negative voltage supplied to the AVSS pin.
+	 * So, we do AVDD - AVSS to compute the DC voltage generated by the bias
+	 * voltage generator.
+	 */
+	if (st->pins_fn[ain_n] & AD4170_PIN_VBIAS) {
+		*ain_voltage = (st->vrefs_uv[AD4170_AVDD_SUP]
+				- st->vrefs_uv[AD4170_AVSS_SUP]) / 2;
+		return 0;
+	}
+
 	if (ain_n <= AD4170_CHAN_MAP_TEMP_SENSOR)
 		return 0;
 
@@ -1742,6 +1816,266 @@ static int ad4170_gpio_init(struct iio_dev *indio_dev)
 	return devm_gpiochip_add_data(&st->spi->dev, &st->gpiochip, indio_dev);
 }
 
+static int _ad4170_find_table_index(const unsigned int *tbl, size_t len,
+				    unsigned int val)
+{
+	unsigned int i;
+
+	for (i = 0; i < len; i++)
+		if (tbl[i] == val)
+			return i;
+
+	return -EINVAL;
+}
+
+#define ad4170_find_table_index(table, val) \
+	_ad4170_find_table_index(table, ARRAY_SIZE(table), val)
+
+static int ad4170_validate_excitation_pins(struct ad4170_state *st,
+					   u32 *exc_pins, int num_exc_pins)
+{
+	struct device *dev = &st->spi->dev;
+	int ret, i;
+
+	for (i = 0; i < num_exc_pins; i++) {
+		unsigned int pin = exc_pins[i];
+
+		ret = ad4170_find_table_index(ad4170_iout_pin_tbl, pin);
+		if (ret < 0)
+			return dev_err_probe(dev, ret,
+					     "Invalid excitation pin: %u\n",
+					     pin);
+
+		if (pin <= AD4170_MAX_ANALOG_PINS) {
+			if (st->pins_fn[pin] != AD4170_PIN_UNASIGNED)
+				return dev_err_probe(dev, -EINVAL,
+						     "Pin %u already used with fn %u\n",
+						     pin, st->pins_fn[pin]);
+
+			st->pins_fn[pin] |= AD4170_PIN_CURRENT_OUT;
+		} else {
+			unsigned int gpio = pin - AD4170_CURRENT_SRC_I_OUT_PIN_GPIO0;
+
+			if (st->gpio_fn[gpio] != AD4170_GPIO_UNASIGNED)
+				return dev_err_probe(dev, -EINVAL,
+						     "GPIO %u already used with fn %u\n",
+						     gpio, st->gpio_fn[gpio]);
+
+			st->gpio_fn[gpio] |= AD4170_GPIO_AC_EXCITATION;
+		}
+	}
+	return 0;
+}
+
+static int ad4170_setup_current_src(struct ad4170_state *st,
+				    struct fwnode_handle *child,
+				    struct ad4170_setup *setup, u32 *exc_pins,
+				    int num_exc_pins, int exc_cur, bool ac_excited)
+{
+	unsigned int current_src, i, j;
+	int ret;
+
+	for (i = 0; i < num_exc_pins; i++) {
+		unsigned int pin = exc_pins[i];
+
+		current_src |= FIELD_PREP(AD4170_CURRENT_SRC_I_OUT_PIN_MSK, pin);
+		current_src |= FIELD_PREP(AD4170_CURRENT_SRC_I_OUT_VAL_MSK, exc_cur);
+
+		for (j = 0; j < AD4170_NUM_CURRENT_SRC; j++) {
+			/*
+			 * Excitation current chopping is configured in pairs.
+			 * If current chopping configured and the first end of
+			 * the current source pair has already been assigned,
+			 * skip to the next pair of output currents.
+			 */
+			if (ac_excited && j % 2 != 0)
+				continue;
+
+			if (st->cur_src_pins[j] == AD4170_CURRENT_SRC_DISABLED) {
+				st->cur_src_pins[j] = pin;
+				break;
+			}
+		}
+		if (j == AD4170_NUM_CURRENT_SRC)
+			return dev_err_probe(&st->spi->dev, -EINVAL,
+					     "Failed to setup IOUT at pin %u\n",
+					     pin);
+
+		ret = regmap_write(st->regmap, AD4170_CURRENT_SRC_REG(j),
+				   current_src);
+		if (ret)
+			return ret;
+	}
+
+	if (ac_excited && num_exc_pins > 1) {
+		unsigned int exc_cur_pair;
+
+		if (st->cur_src_pins[0] == exc_pins[0])
+			exc_cur_pair = 1;
+		else
+			exc_cur_pair = 2;
+
+		/*
+		 * Configure excitation currents chopping.
+		 * Chop two pairs if using four excitation currents.
+		 */
+		setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_IEXC_MSK,
+					  num_exc_pins == 2 ? exc_cur_pair : 3);
+	}
+
+	return 0;
+}
+
+static int ad4170_setup_bridge(struct ad4170_state *st,
+			       struct fwnode_handle *child,
+			       struct ad4170_setup *setup, u32 *exc_pins,
+			       int num_exc_pins, int exc_cur, bool ac_excited)
+{
+	int ret;
+
+	/*
+	 * If a specific current is provided through
+	 * adi,excitation-current-microamp, set excitation pins provided through
+	 * adi,excitation-pins to AC excite the bridge circuit. Else, use
+	 * predefined ACX1, ACX1 negated, ACX2, ACX2 negated signals to AC
+	 * excite the bridge. Those signals are output on GPIO2, GPIO0, GPIO3,
+	 * and GPIO1, respectively. If only two pins are specified for AC
+	 * excitation, use ACX1 and ACX2.
+	 *
+	 * Also, to avoid any short-circuit condition when more than one channel
+	 * is enabled, set GPIO2 and GPIO0 high, and set GPIO1 and GPIO3 low to
+	 * DC excite the bridge whenever a channel without AC excitation is
+	 * selected. That is needed because GPIO pins are controlled by the next
+	 * highest priority GPIO function when a channel doesn't enable AC
+	 * excitation. See datasheet Figure 113 Weigh Scale (AC Excitation) for
+	 * an example circuit diagram.
+	 */
+	if (exc_cur == 0 && ac_excited) {
+		if (num_exc_pins == 2) {
+			setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_ADC_MSK, 0x3);
+			ret = regmap_set_bits(st->regmap,
+					      AD4170_GPIO_MODE_REG,
+					      BIT(7) | BIT(5));
+			if (ret)
+				return ret;
+
+			ret = regmap_set_bits(st->regmap,
+					      AD4170_GPIO_OUTPUT_REG,
+					      BIT(3) | BIT(2));
+			if (ret)
+				return ret;
+
+			st->gpio_fn[3] |= AD4170_GPIO_OUTPUT;
+			st->gpio_fn[2] |= AD4170_GPIO_OUTPUT;
+		} else {
+			setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_ADC_MSK, 0x2);
+			ret = regmap_set_bits(st->regmap,
+					      AD4170_GPIO_MODE_REG,
+					      BIT(7) | BIT(5) | BIT(3) | BIT(1));
+			if (ret)
+				return ret;
+
+			ret = regmap_set_bits(st->regmap,
+					      AD4170_GPIO_OUTPUT_REG,
+					      BIT(3) | BIT(2) | BIT(1) | BIT(0));
+			if (ret)
+				return ret;
+
+			st->gpio_fn[3] |= AD4170_GPIO_OUTPUT;
+			st->gpio_fn[2] |= AD4170_GPIO_OUTPUT;
+			st->gpio_fn[1] |= AD4170_GPIO_OUTPUT;
+			st->gpio_fn[0] |= AD4170_GPIO_OUTPUT;
+		}
+
+		return 0;
+	}
+
+	return ad4170_setup_current_src(st, child, setup, exc_pins,
+					num_exc_pins, exc_cur, ac_excited);
+}
+
+static int ad4170_setup_rtd(struct ad4170_state *st,
+			    struct fwnode_handle *child,
+			    struct ad4170_setup *setup, u32 *exc_pins,
+			    int num_exc_pins, int exc_cur, bool ac_excited)
+{
+	return ad4170_setup_current_src(st, child, setup, exc_pins,
+					num_exc_pins, exc_cur, ac_excited);
+}
+
+static int ad4170_parse_external_sensor(struct ad4170_state *st,
+					struct fwnode_handle *child,
+					struct ad4170_setup *setup,
+					struct iio_chan_spec *chan, u8 s_type)
+{
+	unsigned int num_exc_pins, exc_cur, reg_val;
+	struct device *dev = &st->spi->dev;
+	u32 pins[2], exc_pins[4];
+	bool ac_excited, vbias;
+	int ret;
+
+	ret = fwnode_property_read_u32_array(child, "diff-channels", pins,
+					     ARRAY_SIZE(pins));
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to read sensor diff-channels\n");
+
+	chan->differential = true;
+	chan->channel = pins[0];
+	chan->channel2 = pins[1];
+
+	ac_excited = fwnode_property_read_bool(child, "adi,excitation-ac");
+
+	num_exc_pins = fwnode_property_count_u32(child, "adi,excitation-pins");
+	if (num_exc_pins != 1 && num_exc_pins != 2 && num_exc_pins != 4)
+		return dev_err_probe(dev, -EINVAL,
+				     "Invalid number of excitation pins\n");
+
+	ret = fwnode_property_read_u32_array(child, "adi,excitation-pins",
+					     exc_pins, num_exc_pins);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to read adi,excitation-pins\n");
+
+	ret = ad4170_validate_excitation_pins(st, exc_pins, num_exc_pins);
+	if (ret)
+		return ret;
+
+	exc_cur = 0;
+	ret = fwnode_property_read_u32(child, "adi,excitation-current-microamp",
+				       &exc_cur);
+	if (ret && s_type == AD4170_RTD_SENSOR)
+		return dev_err_probe(dev, ret,
+				     "Failed to read adi,excitation-current-microamp\n");
+
+	ret = ad4170_find_table_index(ad4170_iout_current_ua_tbl, exc_cur);
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "Invalid excitation current: %uuA\n",
+				     exc_cur);
+
+	/* Get the excitation current configuration value */
+	exc_cur = ret;
+
+	if (s_type == AD4170_THERMOCOUPLE_SENSOR) {
+		vbias = fwnode_property_read_bool(child, "adi,vbias");
+		if (vbias) {
+			st->pins_fn[chan->channel2] |= AD4170_PIN_VBIAS;
+			reg_val = BIT(chan->channel2);
+			return regmap_write(st->regmap, AD4170_V_BIAS_REG,
+					    reg_val);
+		}
+	}
+	if (s_type == AD4170_WEIGH_SCALE_SENSOR) {
+		ret = ad4170_setup_bridge(st, child, setup, exc_pins,
+					  num_exc_pins, exc_cur, ac_excited);
+	} else {
+		ret = ad4170_setup_rtd(st, child, setup, exc_pins, num_exc_pins,
+				       exc_cur, ac_excited);
+	}
+	return ret;
+}
+
 static int ad4170_parse_reference(struct ad4170_state *st,
 				  struct fwnode_handle *child,
 				  struct ad4170_setup *setup)
@@ -1823,6 +2157,7 @@ static int ad4170_parse_channel_node(struct iio_dev *indio_dev,
 	struct ad4170_state *st = iio_priv(indio_dev);
 	struct device *dev = &st->spi->dev;
 	struct ad4170_chan_info *chan_info;
+	u8 s_type = AD4170_ADC_SENSOR;
 	struct ad4170_setup *setup;
 	struct iio_chan_spec *chan;
 	unsigned int ch_reg;
@@ -1854,10 +2189,34 @@ static int ad4170_parse_channel_node(struct iio_dev *indio_dev,
 	if (ret)
 		return ret;
 
-	ret = ad4170_parse_adc_channel_type(dev, child, chan);
-	if (ret < 0)
-		return ret;
+	ret = fwnode_property_read_u8(child, "adi,sensor-type", &s_type);
+	if (!ret) {
+		if (s_type > AD4170_THERMOCOUPLE_SENSOR)
+			return dev_err_probe(dev, ret,
+					     "Invalid adi,sensor-type: %u\n",
+					     s_type);
+	}
+	switch (s_type) {
+	case AD4170_ADC_SENSOR:
+		ret = ad4170_parse_adc_channel_type(dev, child, chan);
+		if (ret < 0)
+			return ret;
+
+		break;
+	case AD4170_WEIGH_SCALE_SENSOR:
+		fallthrough;
+	case AD4170_THERMOCOUPLE_SENSOR:
+		fallthrough;
+	case AD4170_RTD_SENSOR:
+		ret = ad4170_parse_external_sensor(st, child, setup, chan,
+						   s_type);
+		if (ret < 0)
+			return ret;
 
+		break;
+	default:
+		return -EINVAL;
+	}
 	bipolar = fwnode_property_read_bool(child, "bipolar");
 	setup->afe |= FIELD_PREP(AD4170_AFE_BIPOLAR_MSK, bipolar);
 	if (bipolar)
@@ -2059,6 +2418,12 @@ static int ad4170_parse_firmware(struct iio_dev *indio_dev)
 	for (i = 0; i < AD4170_NUM_ANALOG_PINS; i++)
 		st->pins_fn[i] = AD4170_PIN_UNASIGNED;
 
+	for (i = 0; i < AD4170_NUM_GPIO_PINS; i++)
+		st->gpio_fn[i] = AD4170_GPIO_UNASIGNED;
+
+	for (i = 0; i < AD4170_NUM_CURRENT_SRC; i++)
+		st->cur_src_pins[i] = AD4170_CURRENT_SRC_DISABLED;
+
 	/* On power on, device defaults to using SDO pin for data ready signal */
 	st->int_pin_sel = AD4170_INT_PIN_SDO;
 	ret = device_property_match_property_string(dev, "interrupt-names",
@@ -2083,6 +2448,10 @@ static int ad4170_parse_firmware(struct iio_dev *indio_dev)
 
 	/* Only create a GPIO chip if flagged for it */
 	if (device_property_read_bool(&st->spi->dev, "gpio-controller")) {
+		for (i = 0; i < AD4170_NUM_GPIO_PINS; i++)
+			if (st->gpio_fn[i] != AD4170_GPIO_UNASIGNED)
+				return 0;
+
 		ret = ad4170_gpio_init(indio_dev);
 		if (ret)
 			return ret;
-- 
2.47.2