iio: inkern: API for reading available iio channel attribute values

Extend the inkern API with a function for reading available
attribute values of iio channels.

Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/inkern.c

@@ -733,6 +733,26 @@ static int iio_channel_read_avail(struct iio_channel *chan,
 						 vals, type, length, info);
 }
 
+int iio_read_avail_channel_attribute(struct iio_channel *chan,
+				     const int **vals, int *type, int *length,
+				     enum iio_chan_info_enum attribute)
+{
+	int ret;
+
+	mutex_lock(&chan->indio_dev->info_exist_lock);
+	if (!chan->indio_dev->info) {
+		ret = -ENODEV;
+		goto err_unlock;
+	}
+
+	ret = iio_channel_read_avail(chan, vals, type, length, attribute);
+err_unlock:
+	mutex_unlock(&chan->indio_dev->info_exist_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_read_avail_channel_attribute);
+
 int iio_read_avail_channel_raw(struct iio_channel *chan,
 			       const int **vals, int *length)
 {

include/linux/iio/consumer.h

@@ -290,6 +290,20 @@ int iio_read_max_channel_raw(struct iio_channel *chan, int *val);
 int iio_read_avail_channel_raw(struct iio_channel *chan,
 			       const int **vals, int *length);
 
+/**
+ * iio_read_avail_channel_attribute() - read available channel attribute values
+ * @chan:		The channel being queried.
+ * @vals:		Available values read back.
+ * @type:		Type of values read back.
+ * @length:		Number of entries in vals.
+ * @attribute:		info attribute to be read back.
+ *
+ * Returns an error code, IIO_AVAIL_RANGE or IIO_AVAIL_LIST.
+ */
+int iio_read_avail_channel_attribute(struct iio_channel *chan,
+				     const int **vals, int *type, int *length,
+				     enum iio_chan_info_enum attribute);
+
 /**
  * iio_get_channel_type() - get the type of a channel
  * @channel:		The channel being queried.