staging: iio: resolver: ad2s1210: implement IIO_CHAN_INFO_SCALE

This adds an implementation of IIO_CHAN_INFO_SCALE to the ad2s1210
resolver driver. This allows userspace to get the scale factor for the
raw values.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20230929-ad2s1210-mainline-v3-8-fa4364281745@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1210.c

@@ -461,13 +461,10 @@ static ssize_t ad2s1210_store_reg(struct device *dev,
 	return ret < 0 ? ret : len;
 }
 
-static int ad2s1210_read_raw(struct iio_dev *indio_dev,
+static int ad2s1210_single_conversion(struct ad2s1210_state *st,
 				      struct iio_chan_spec const *chan,
-			     int *val,
-			     int *val2,
-			     long m)
+				      int *val)
 {
-	struct ad2s1210_state *st = iio_priv(indio_dev);
 	int ret = 0;
 
 	mutex_lock(&st->lock);
@@ -514,6 +511,44 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
 	return ret;
 }
 
+static const int ad2s1210_velocity_scale[] = {
+	17089132, /* 8.192MHz / (2*pi * 2500 / 2^15) */
+	42722830, /* 8.192MHz / (2*pi * 1000 / 2^15) */
+	85445659, /* 8.192MHz / (2*pi * 500 / 2^15) */
+	341782638, /* 8.192MHz / (2*pi * 125 / 2^15) */
+};
+
+static int ad2s1210_read_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_RAW:
+		return ad2s1210_single_conversion(st, chan, val);
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_ANGL:
+			/* approx 0.3 arc min converted to radians */
+			*val = 0;
+			*val2 = 95874;
+			return IIO_VAL_INT_PLUS_NANO;
+		case IIO_ANGL_VEL:
+			*val = st->fclkin;
+			*val2 = ad2s1210_velocity_scale[st->resolution];
+			return IIO_VAL_FRACTIONAL;
+		default:
+			return -EINVAL;
+		}
+
+	default:
+		return -EINVAL;
+	}
+}
+
 static IIO_DEVICE_ATTR(fclkin, 0644,
 		       ad2s1210_show_fclkin, ad2s1210_store_fclkin, 0);
 static IIO_DEVICE_ATTR(fexcit, 0644,
@@ -552,12 +587,14 @@ static const struct iio_chan_spec ad2s1210_channels[] = {
 		.type = IIO_ANGL,
 		.indexed = 1,
 		.channel = 0,
-		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
 	}, {
 		.type = IIO_ANGL_VEL,
 		.indexed = 1,
 		.channel = 0,
-		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
 	}
 };