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

Marcelo Schmitt
2025-04-28T12:30:13Z

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