staging: iio: resolver: ad2s1210: implement hysteresis as channel attr

The AD2S1210 resolver has a hysteresis feature that can be used to
prevent flicker in the LSB of the position register. This can be either
enabled or disabled. Disabling hysteresis is useful for increasing
precision by oversampling.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231005-ad2s1210-mainline-v4-2-ec00746840fc@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1210.c

@@ -76,7 +76,8 @@ struct ad2s1210_state {
 	struct regmap *regmap;
 	/** The external oscillator frequency in Hz. */
 	unsigned long clkin_hz;
-	bool hysteresis;
+	/** Available raw hysteresis values based on resolution. */
+	int hysteresis_available[2];
 	u8 resolution;
 	/** For reading raw sample value via SPI. */
 	__be16 sample __aligned(IIO_DMA_MINALIGN);
@@ -311,6 +312,7 @@ static ssize_t ad2s1210_store_resolution(struct device *dev,
 		goto error_ret;
 
 	st->resolution = udata;
+	st->hysteresis_available[1] = 1 << (16 - st->resolution);
 	ret = len;
 
 error_ret:
@@ -447,6 +449,35 @@ static int ad2s1210_single_conversion(struct ad2s1210_state *st,
 	return ret;
 }
 
+static int ad2s1210_get_hysteresis(struct ad2s1210_state *st, int *val)
+{
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_test_bits(st->regmap, AD2S1210_REG_CONTROL,
+			       AD2S1210_ENABLE_HYSTERESIS);
+	mutex_unlock(&st->lock);
+
+	if (ret < 0)
+		return ret;
+
+	*val = ret << (16 - st->resolution);
+	return IIO_VAL_INT;
+}
+
+static int ad2s1210_set_hysteresis(struct ad2s1210_state *st, int val)
+{
+	int ret;
+
+	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);
+
+	return ret;
+}
+
 static const int ad2s1210_velocity_scale[] = {
 	17089132, /* 8.192MHz / (2*pi * 2500 / 2^15) */
 	42722830, /* 8.192MHz / (2*pi * 1000 / 2^15) */
@@ -479,7 +510,55 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
 		default:
 			return -EINVAL;
 		}
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			return ad2s1210_get_hysteresis(st, val);
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+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)
+{
+	struct ad2s1210_state *st = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			*vals = st->hysteresis_available;
+			*type = IIO_VAL_INT;
+			*length = ARRAY_SIZE(st->hysteresis_available);
+			return IIO_AVAIL_LIST;
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
 
+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);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HYSTERESIS:
+		switch (chan->type) {
+		case IIO_ANGL:
+			return ad2s1210_set_hysteresis(st, val);
+		default:
+			return -EINVAL;
+		}
 	default:
 		return -EINVAL;
 	}
@@ -520,7 +599,10 @@ static const struct iio_chan_spec ad2s1210_channels[] = {
 		.indexed = 1,
 		.channel = 0,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-				      BIT(IIO_CHAN_INFO_SCALE),
+				      BIT(IIO_CHAN_INFO_SCALE) |
+				      BIT(IIO_CHAN_INFO_HYSTERESIS),
+		.info_mask_separate_available =
+					BIT(IIO_CHAN_INFO_HYSTERESIS),
 	}, {
 		.type = IIO_ANGL_VEL,
 		.indexed = 1,
@@ -596,6 +678,8 @@ static int ad2s1210_debugfs_reg_access(struct iio_dev *indio_dev,
 
 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,
 };
@@ -711,8 +795,9 @@ static int ad2s1210_probe(struct spi_device *spi)
 
 	mutex_init(&st->lock);
 	st->sdev = spi;
-	st->hysteresis = true;
 	st->resolution = 12;
+	st->hysteresis_available[0] = 0;
+	st->hysteresis_available[1] = 1 << (16 - st->resolution);
 
 	ret = ad2s1210_setup_clocks(st);
 	if (ret < 0)