Re: [PATCH v1 7/7] iio: adc: ad4170: Add support for weigh scale and RTD sensors

From: Nuno Sá
Date: Thu Apr 10 2025 - 06:40:00 EST

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In reply to: Marcelo Schmitt: "[PATCH v1 7/7] iio: adc: ad4170: Add support for weigh scale and RTD sensors"
Next in thread: Marcelo Schmitt: "Re: [PATCH v1 7/7] iio: adc: ad4170: Add support for weigh scale and RTD sensors"
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On Wed, 2025-04-09 at 09:26 -0300, Marcelo Schmitt wrote:
> 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@xxxxxxxxxx>
> ---
> drivers/iio/adc/ad4170.c | 341 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 338 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/adc/ad4170.c b/drivers/iio/adc/ad4170.c
> index d204f8ca840f..2cf578608316 100644
> --- a/drivers/iio/adc/ad4170.c
> +++ b/drivers/iio/adc/ad4170.c
> @@ -77,6 +77,7 @@
> #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_FIR_CTRL 0x141
> #define AD4170_COEFF_DATA_REG 0x14A
> #define AD4170_COEFF_ADDR_REG 0x14C
> @@ -127,6 +128,10 @@
> /* 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 */
> @@ -188,6 +193,21 @@
> #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
> @@ -222,6 +242,12 @@
> #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
>
> enum ad4170_ref_buf {
> AD4170_REF_BUF_PRE, /* Pre-charge referrence buffer */
> @@ -278,6 +304,33 @@ 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_ADC_SENSOR = 0,
> + AD4170_WEIGH_SCALE_SENSOR = 1,
> + AD4170_THERMOCOUPLE_SENSOR = 2,
> + AD4170_RTD_SENSOR = 3,
> +};
> +
> static const char * const ad4170_chip_names[] = {
> "ad4170",
> "ad4190",
> @@ -343,6 +396,7 @@ 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];
> struct gpio_chip gpiochip;
> u32 int_pin_sel;
> int
> sps_tbl[ARRAY_SIZE(ad4170_filt_names)][AD4170_MAX_FS_TBL_SIZE][2];
> @@ -956,6 +1010,19 @@ 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;
>
> @@ -1746,6 +1813,242 @@ 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_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)
> +{
> + int current_src, ret, i;
> +
> + 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);
> +
> + ret = regmap_write(st->regmap16, AD4170_CURRENT_SRC_REG(i),
> +    current_src);
> + if (ret)
> + return ret;
> + }
> +
> + if (ac_excited)
> + setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_IEXC_MSK,
> + num_exc_pins == 2 ? 0x2 : 0x3);
> +
> + return 0;
> +}

In the above I do not see any explicit GPIO configuration which makes me wonder
if having the RTD is mutual exclusive with having GPIOs?

> +
> +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 current_src, ret, i;
> +
> + if (!ac_excited)
> + return 0;

Same as above, if !ac_excited, can't we use the GPIOs? because
ad4170_validate_excitation_pins() just unconditionally sets
AD4170_GPIO_AC_EXCITATION. Or maybe this DT property is only adding
complexity... See below
> +
> + /*
> + * 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. See AD4170 datasheet for
> instructions
> + * on how to setup the bridge circuit.
> + *
> + * 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) {
> + if (num_exc_pins == 2) {
> + setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_ADC_MSK,
> 0x3);
> + ret = regmap_set_bits(st->regmap16,
> +       AD4170_GPIO_MODE_REG,
> +       BIT(7) | BIT(5));
> + if (ret)
> + return ret;
> +
> + ret = regmap_set_bits(st->regmap16,
> +       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->regmap16,
> +       AD4170_GPIO_MODE_REG,
> +       BIT(7) | BIT(5) | BIT(3) |
> BIT(1));
> + if (ret)
> + return ret;
> +
> + ret = regmap_set_bits(st->regmap16,
> +       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;

Not sure if you gain much with having the funcs OR'ed like this... If I'm not
missing nothing it's only about logging in ad4170_validate_excitation_pins()?
It's up to you but I would consider using bitmaps (unsigned long) for this and
just test the bits.

> + }
> +
> + return 0;
> + }
> + 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);
> +
> + ret = regmap_write(st->regmap16, AD4170_CURRENT_SRC_REG(i),
> +    current_src);
> + if (ret)
> + return ret;
> + }
> +
> + setup->misc |= FIELD_PREP(AD4170_MISC_CHOP_IEXC_MSK,
> + num_exc_pins == 2 ? 0x2 : 0x3);
> +
> + return 0;
> +}
> +
> +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,ac-excited");
> +
> + num_exc_pins = fwnode_property_count_u32(child, "adi,excitation-
> pins");
> + if (num_exc_pins != 2 && num_exc_pins != 4)
> + return dev_err_probe(dev, -EINVAL,
> +      "Invalid number of excitation pins\n");

Can't we assume that a valid num_exc_pins property means ac_excited = true?
Because that looks to be the logic in ad4170_validate_excitation_pins().

> +
> + 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->regmap16, AD4170_V_BIAS_REG,
> +     reg_val);
> + }
> + }
> + if (s_type == AD4170_WEIGH_SCALE_SENSOR ||
> +     s_type == AD4170_THERMOCOUPLE_SENSOR) {

I guess you have this because of indentation levels but is it that bad if we do
if (s_typ == AD4170_THERMOCOUPLE_SENSOR && fwnode_property_read_bool(child, "adi,vbias") {
...
}

> + 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)
> @@ -1827,6 +2130,7 @@ 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;
> @@ -1857,10 +2161,34 @@ 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_RTD_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)
> @@ -2057,6 +2385,9 @@ 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;
> +
> /* 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",
> @@ -2081,6 +2412,10 @@ 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;

I think you could improve this... You're taking an all or nothing approach.
IIUC, we can have cases where only two GPIOs are in use which means we could use
the other 2? There the gpiochio init_valid_mask() call that you could
potentially use.

- Nuno Sá

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