iio: resolver: ad2s1210: add support for adi,fixed-mode

It is possible to use the AD2S1210 with hardwired mode pins (A0 and A1).
According to the devicetree bindings, in this case the adi,fixed-mode
property will specify which of the 3 possible modes the mode pins are
hardwired for and the gpio-modes property is not allowed.

This adds support for the case where the mode pins are hardwired for
config mode. In this configuration, the position and value must be read
from the config register.

The case of hardwired position or velocity mode is not supported as
there would be no way to configure the device.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20231016135423.16808-1-dlechner@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: dlech

drivers/iio/resolver/ad2s1210.c

@@ -141,14 +141,16 @@ struct ad2s1210_state {
 	struct spi_device *sdev;
 	/** GPIO pin connected to SAMPLE line. */
 	struct gpio_desc *sample_gpio;
-	/** GPIO pins connected to A0 and A1 lines. */
+	/** GPIO pins connected to A0 and A1 lines (optional). */
 	struct gpio_descs *mode_gpios;
 	/** Used to access config registers. */
 	struct regmap *regmap;
 	/** The external oscillator frequency in Hz. */
 	unsigned long clkin_hz;
 	/** Available raw hysteresis values based on resolution. */
 	int hysteresis_available[2];
+	/* adi,fixed-mode property - only valid when mode_gpios == NULL. */
+	enum ad2s1210_mode fixed_mode;
 	/** The selected resolution */
 	enum ad2s1210_resolution resolution;
 	/** Copy of fault register from the previous read. */
@@ -175,6 +177,9 @@ static int ad2s1210_set_mode(struct ad2s1210_state *st, enum ad2s1210_mode mode)
 	struct gpio_descs *gpios = st->mode_gpios;
 	DECLARE_BITMAP(bitmap, 2);
 
+	if (!gpios)
+		return mode == st->fixed_mode ? 0 : -EOPNOTSUPP;
+
 	bitmap[0] = mode;
 
 	return gpiod_set_array_value(gpios->ndescs, gpios->desc, gpios->info,
@@ -276,7 +281,8 @@ static int ad2s1210_regmap_reg_read(void *context, unsigned int reg,
 	 * 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)
+	if ((reg > AD2S1210_REG_VELOCITY_LSB && reg != AD2S1210_REG_FAULT)
+	     && st->rx[1] & AD2S1210_ADDRESS_DATA)
 		return -EBADMSG;
 
 	*val = st->rx[1];
@@ -450,21 +456,53 @@ static int ad2s1210_single_conversion(struct iio_dev *indio_dev,
 	ad2s1210_toggle_sample_line(st);
 	timestamp = iio_get_time_ns(indio_dev);
 
-	switch (chan->type) {
-	case IIO_ANGL:
-		ret = ad2s1210_set_mode(st, MOD_POS);
-		break;
-	case IIO_ANGL_VEL:
-		ret = ad2s1210_set_mode(st, MOD_VEL);
-		break;
-	default:
-		return -EINVAL;
+	if (st->fixed_mode == MOD_CONFIG) {
+		unsigned int reg_val;
+
+		switch (chan->type) {
+		case IIO_ANGL:
+			ret = regmap_bulk_read(st->regmap,
+					       AD2S1210_REG_POSITION_MSB,
+					       &st->sample.raw, 2);
+			if (ret < 0)
+				return ret;
+
+			break;
+		case IIO_ANGL_VEL:
+			ret = regmap_bulk_read(st->regmap,
+					       AD2S1210_REG_VELOCITY_MSB,
+					       &st->sample.raw, 2);
+			if (ret < 0)
+				return ret;
+
+			break;
+		default:
+			return -EINVAL;
+		}
+
+		ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &reg_val);
+		if (ret < 0)
+			return ret;
+
+		st->sample.fault = reg_val;
+	} else {
+		switch (chan->type) {
+		case IIO_ANGL:
+			ret = ad2s1210_set_mode(st, MOD_POS);
+			break;
+		case IIO_ANGL_VEL:
+			ret = ad2s1210_set_mode(st, MOD_VEL);
+			break;
+		default:
+			return -EINVAL;
+		}
+		if (ret < 0)
+			return ret;
+
+		ret = spi_read(st->sdev, &st->sample, 3);
+		if (ret < 0)
+			return ret;
 	}
-	if (ret < 0)
-		return ret;
-	ret = spi_read(st->sdev, &st->sample, 3);
-	if (ret < 0)
-		return ret;
 
 	switch (chan->type) {
 	case IIO_ANGL:
@@ -1252,27 +1290,53 @@ static irqreturn_t ad2s1210_trigger_handler(int irq, void *p)
 	ad2s1210_toggle_sample_line(st);
 
 	if (test_bit(0, indio_dev->active_scan_mask)) {
-		ret = ad2s1210_set_mode(st, MOD_POS);
-		if (ret < 0)
-			goto error_ret;
-
-		ret = spi_read(st->sdev, &st->sample, 3);
-		if (ret < 0)
-			goto error_ret;
+		if (st->fixed_mode == MOD_CONFIG) {
+			ret = regmap_bulk_read(st->regmap,
+					       AD2S1210_REG_POSITION_MSB,
+					       &st->sample.raw, 2);
+			if (ret < 0)
+				goto error_ret;
+		} else {
+			ret = ad2s1210_set_mode(st, MOD_POS);
+			if (ret < 0)
+				goto error_ret;
+
+			ret = spi_read(st->sdev, &st->sample, 3);
+			if (ret < 0)
+				goto error_ret;
+		}
 
 		memcpy(&st->scan.chan[chan++], &st->sample.raw, 2);
 	}
 
 	if (test_bit(1, indio_dev->active_scan_mask)) {
-		ret = ad2s1210_set_mode(st, MOD_VEL);
-		if (ret < 0)
-			goto error_ret;
+		if (st->fixed_mode == MOD_CONFIG) {
+			ret = regmap_bulk_read(st->regmap,
+					       AD2S1210_REG_VELOCITY_MSB,
+					       &st->sample.raw, 2);
+			if (ret < 0)
+				goto error_ret;
+		} else {
+			ret = ad2s1210_set_mode(st, MOD_VEL);
+			if (ret < 0)
+				goto error_ret;
+
+			ret = spi_read(st->sdev, &st->sample, 3);
+			if (ret < 0)
+				goto error_ret;
+		}
 
-		ret = spi_read(st->sdev, &st->sample, 3);
+		memcpy(&st->scan.chan[chan++], &st->sample.raw, 2);
+	}
+
+	if (st->fixed_mode == MOD_CONFIG) {
+		unsigned int reg_val;
+
+		ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &reg_val);
 		if (ret < 0)
-			goto error_ret;
+			return ret;
 
-		memcpy(&st->scan.chan[chan++], &st->sample.raw, 2);
+		st->sample.fault = reg_val;
 	}
 
 	ad2s1210_push_events(indio_dev, st->sample.fault, pf->timestamp);
@@ -1299,9 +1363,24 @@ static const struct iio_info ad2s1210_info = {
 static int ad2s1210_setup_properties(struct ad2s1210_state *st)
 {
 	struct device *dev = &st->sdev->dev;
+	const char *str_val;
 	u32 val;
 	int ret;
 
+	ret = device_property_read_string(dev, "adi,fixed-mode", &str_val);
+	if (ret == -EINVAL)
+		st->fixed_mode = -1;
+	else if (ret < 0)
+		return dev_err_probe(dev, ret,
+			"failed to read adi,fixed-mode property\n");
+	else {
+		if (strcmp(str_val, "config"))
+			return dev_err_probe(dev, -EINVAL,
+				"only adi,fixed-mode=\"config\" is supported\n");
+
+		st->fixed_mode = MOD_CONFIG;
+	}
+
 	ret = device_property_read_u32(dev, "assigned-resolution-bits", &val);
 	if (ret < 0)
 		return dev_err_probe(dev, ret,
@@ -1357,12 +1436,21 @@ static int ad2s1210_setup_gpios(struct ad2s1210_state *st)
 				     "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);
+	st->mode_gpios = devm_gpiod_get_array_optional(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)
+	if (!st->mode_gpios && st->fixed_mode == -1)
+		return dev_err_probe(dev, -EINVAL,
+			"must specify either adi,fixed-mode or mode-gpios\n");
+
+	if (st->mode_gpios && st->fixed_mode != -1)
+		return dev_err_probe(dev, -EINVAL,
+			"must specify only one of adi,fixed-mode or mode-gpios\n");
+
+	if (st->mode_gpios && st->mode_gpios->ndescs != 2)
 		return dev_err_probe(dev, -EINVAL,
 				     "requires exactly 2 mode-gpios\n");