iio: inkern: add helpers to query available values from channels

Specifically a helper for reading the available maximum raw value of a
channel and a helper for forwarding read_avail requests for raw values
from one iio driver to an iio channel that is consumed.

These rather specific helpers are in turn built with generic helpers
making it easy to build more helpers for available values as needed.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/inkern.c

@@ -716,6 +716,110 @@ int iio_read_channel_scale(struct iio_channel *chan, int *val, int *val2)
 }
 EXPORT_SYMBOL_GPL(iio_read_channel_scale);
 
+static int iio_channel_read_avail(struct iio_channel *chan,
+				  const int **vals, int *type, int *length,
+				  enum iio_chan_info_enum info)
+{
+	if (!iio_channel_has_available(chan->channel, info))
+		return -EINVAL;
+
+	return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
+						 vals, type, length, info);
+}
+
+int iio_read_avail_channel_raw(struct iio_channel *chan,
+			       const int **vals, int *length)
+{
+	int ret;
+	int type;
+
+	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, IIO_CHAN_INFO_RAW);
+err_unlock:
+	mutex_unlock(&chan->indio_dev->info_exist_lock);
+
+	if (ret >= 0 && type != IIO_VAL_INT) {
+		/* raw values are assumed to be IIO_VAL_INT */
+		ret = -EINVAL;
+		goto err_unlock;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_read_avail_channel_raw);
+
+static int iio_channel_read_max(struct iio_channel *chan,
+				int *val, int *val2, int *type,
+				enum iio_chan_info_enum info)
+{
+	int unused;
+	const int *vals;
+	int length;
+	int ret;
+
+	if (!val2)
+		val2 = &unused;
+
+	ret = iio_channel_read_avail(chan, &vals, type, &length, info);
+	switch (ret) {
+	case IIO_AVAIL_RANGE:
+		switch (*type) {
+		case IIO_VAL_INT:
+			*val = vals[2];
+			break;
+		default:
+			*val = vals[4];
+			*val2 = vals[5];
+		}
+		return 0;
+
+	case IIO_AVAIL_LIST:
+		if (length <= 0)
+			return -EINVAL;
+		switch (*type) {
+		case IIO_VAL_INT:
+			*val = vals[--length];
+			while (length) {
+				if (vals[--length] > *val)
+					*val = vals[length];
+			}
+			break;
+		default:
+			/* FIXME: learn about max for other iio values */
+			return -EINVAL;
+		}
+		return 0;
+
+	default:
+		return ret;
+	}
+}
+
+int iio_read_max_channel_raw(struct iio_channel *chan, int *val)
+{
+	int ret;
+	int type;
+
+	mutex_lock(&chan->indio_dev->info_exist_lock);
+	if (!chan->indio_dev->info) {
+		ret = -ENODEV;
+		goto err_unlock;
+	}
+
+	ret = iio_channel_read_max(chan, val, NULL, &type, IIO_CHAN_INFO_RAW);
+err_unlock:
+	mutex_unlock(&chan->indio_dev->info_exist_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_read_max_channel_raw);
+
 int iio_get_channel_type(struct iio_channel *chan, enum iio_chan_type *type)
 {
 	int ret = 0;