iio: inkern: Add a helper to query an available minimum raw value

A helper, iio_read_max_channel_raw() exists to read the available
maximum raw value of a channel but nothing similar exists to read the
available minimum raw value.

This new helper, iio_read_min_channel_raw(), fills the hole and can be
used for reading the available minimum raw value of a channel.
It is fully based on the existing iio_read_max_channel_raw().
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20230623085830.749991-11-herve.codina@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/iio/inkern.c

@@ -909,6 +909,69 @@ int iio_read_max_channel_raw(struct iio_channel *chan, int *val)
 }
 EXPORT_SYMBOL_GPL(iio_read_max_channel_raw);
 
+static int iio_channel_read_min(struct iio_channel *chan,
+				int *val, int *val2, int *type,
+				enum iio_chan_info_enum info)
+{
+	const int *vals;
+	int length;
+	int ret;
+
+	ret = iio_channel_read_avail(chan, &vals, type, &length, info);
+	if (ret < 0)
+		return ret;
+
+	switch (ret) {
+	case IIO_AVAIL_RANGE:
+		switch (*type) {
+		case IIO_VAL_INT:
+			*val = vals[0];
+			break;
+		default:
+			*val = vals[0];
+			if (val2)
+				*val2 = vals[1];
+		}
+		return 0;
+
+	case IIO_AVAIL_LIST:
+		if (length <= 0)
+			return -EINVAL;
+		switch (*type) {
+		case IIO_VAL_INT:
+			*val = min_array(vals, length);
+			break;
+		default:
+			/* TODO: learn about min for other iio values */
+			return -EINVAL;
+		}
+		return 0;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+int iio_read_min_channel_raw(struct iio_channel *chan, int *val)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(chan->indio_dev);
+	int ret;
+	int type;
+
+	mutex_lock(&iio_dev_opaque->info_exist_lock);
+	if (!chan->indio_dev->info) {
+		ret = -ENODEV;
+		goto err_unlock;
+	}
+
+	ret = iio_channel_read_min(chan, val, NULL, &type, IIO_CHAN_INFO_RAW);
+err_unlock:
+	mutex_unlock(&iio_dev_opaque->info_exist_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_read_min_channel_raw);
+
 int iio_get_channel_type(struct iio_channel *chan, enum iio_chan_type *type)
 {
 	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(chan->indio_dev);

include/linux/iio/consumer.h

@@ -301,6 +301,18 @@ int iio_write_channel_raw(struct iio_channel *chan, int val);
  */
 int iio_read_max_channel_raw(struct iio_channel *chan, int *val);
 
+/**
+ * iio_read_min_channel_raw() - read minimum available raw value from a given
+ *				channel, i.e. the minimum possible value.
+ * @chan:		The channel being queried.
+ * @val:		Value read back.
+ *
+ * Note, if standard units are required, raw reads from iio channels
+ * need the offset (default 0) and scale (default 1) to be applied
+ * as (raw + offset) * scale.
+ */
+int iio_read_min_channel_raw(struct iio_channel *chan, int *val);
+
 /**
  * iio_read_avail_channel_raw() - read available raw values from a given channel
  * @chan:		The channel being queried.