iio:adxl372: Add filter bandwidth support

This patch adds the option for the user to select the filter bandwidth. The
user can also read the available bandwidths which are always adjusted to be
at most half of the sampling frequency. Furthermore, the currently selected
bandwidth can be read via the read_raw function, while the write_raw sets a
new bandwidth value.

Signed-off-by: Stefan Popa <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/adxl372.c

···
 	400, 800, 1600, 3200, 6400,
 };
 
+static const int adxl372_bw_freq_tbl[5] = {
+	200, 400, 800, 1600, 3200,
+};
+
 struct adxl372_axis_lookup {
 	unsigned int bits;
 	enum adxl372_fifo_format fifo_format;
···
 	.channel2 = IIO_MOD_##axis,					\
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),			\
 	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |		\
-				    BIT(IIO_CHAN_INFO_SAMP_FREQ),	\
+				    BIT(IIO_CHAN_INFO_SAMP_FREQ) |	\
+		BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),	\
 	.scan_index = index,						\
 	.scan_type = {							\
 		.sign = 's',						\
···
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		*val = adxl372_samp_freq_tbl[st->odr];
 		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
+		*val = adxl372_bw_freq_tbl[st->bw];
+		return IIO_VAL_INT;
 	}
 
 	return -EINVAL;
···
 			     int val, int val2, long info)
 {
 	struct adxl372_state *st = iio_priv(indio_dev);
-	int odr_index, ret;
+	int odr_index, bw_index, ret;
 
 	switch (info) {
 	case IIO_CHAN_INFO_SAMP_FREQ:
···
 			ret = adxl372_set_bandwidth(st, odr_index);
 
 		return ret;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
+		bw_index = adxl372_find_closest_match(adxl372_bw_freq_tbl,
+					ARRAY_SIZE(adxl372_bw_freq_tbl),
+					val);
+		return adxl372_set_bandwidth(st, bw_index);
 	default:
 		return -EINVAL;
 	}
+}
+
+static ssize_t adxl372_show_filter_freq_avail(struct device *dev,
+					      struct device_attribute *attr,
+					      char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct adxl372_state *st = iio_priv(indio_dev);
+	int i;
+	size_t len = 0;
+
+	for (i = 0; i <= st->odr; i++)
+		len += scnprintf(buf + len, PAGE_SIZE - len,
+				 "%d ", adxl372_bw_freq_tbl[i]);
+
+	buf[len - 1] = '\n';
+
+	return len;
 }
 
 static ssize_t adxl372_get_fifo_enabled(struct device *dev,
···
 };
 
 static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("400 800 1600 3200 6400");
+static IIO_DEVICE_ATTR(in_accel_filter_low_pass_3db_frequency_available,
+		       0444, adxl372_show_filter_freq_avail, NULL, 0);
 
 static struct attribute *adxl372_attributes[] = {
 	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
+	&iio_dev_attr_in_accel_filter_low_pass_3db_frequency_available.dev_attr.attr,
 	NULL,
 };