[PATCH v6 07/16] iio: core: add hierarchical channel relationships

[Rodrigo Alencar via B4 Relay]

From: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>

Add parent-child relationship between iio channels by creating a parent
pointer field in iio_chan_spec struct and exposing a sysfs attribute that
returns the parent channel label.

Signed-off-by: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>
---
 drivers/iio/industrialio-core.c | 44 +++++++++++++++++++++++++++++++++++++++++
 include/linux/iio/iio.h         |  5 +++++
 2 files changed, 49 insertions(+)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 9373006235c8..3d12269f26f4 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -854,6 +854,21 @@ static ssize_t iio_read_channel_label(struct device *dev,
 					 to_iio_dev_attr(attr)->c, buf);
 }
 
+static ssize_t iio_read_channel_parent(struct device *dev,
+				       struct device_attribute *attr,
+				       char *buf)
+{
+	const struct iio_chan_spec *parent = to_iio_dev_attr(attr)->c->parent;
+	int len;
+
+	len = __iio_chan_prefix_emit(parent, IIO_SEPARATE, buf, PAGE_SIZE - 1);
+	if (len < 0)
+		return len;
+
+	buf[len - 1] = '\n'; /* replace underscore termination with newline */
+	return len;
+}
+
 static ssize_t iio_read_channel_info(struct device *dev,
 				     struct device_attribute *attr,
 				     char *buf)
@@ -1263,6 +1278,30 @@ static int iio_device_add_channel_label(struct iio_dev *indio_dev,
 	return 1;
 }
 
+static int iio_device_add_channel_parent(struct iio_dev *indio_dev,
+					 struct iio_chan_spec const *chan)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	int ret;
+
+	if (!chan->parent)
+		return 0;
+
+	ret = __iio_add_chan_devattr("parent",
+				     chan,
+				     &iio_read_channel_parent,
+				     NULL,
+				     0,
+				     IIO_SEPARATE,
+				     &indio_dev->dev,
+				     NULL,
+				     &iio_dev_opaque->channel_attr_list);
+	if (ret < 0)
+		return ret;
+
+	return 1;
+}
+
 static int iio_device_add_info_mask_type(struct iio_dev *indio_dev,
 					 struct iio_chan_spec const *chan,
 					 enum iio_shared_by shared_by,
@@ -1401,6 +1440,11 @@ static int iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
 		return ret;
 	attrcount += ret;
 
+	ret = iio_device_add_channel_parent(indio_dev, chan);
+	if (ret < 0)
+		return ret;
+	attrcount += ret;
+
 	if (chan->ext_info) {
 		unsigned int i = 0;
 
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 1c7d12af22da..9470ab8eb726 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -264,6 +264,10 @@ struct iio_scan_type {
  * @ext_info:		Array of extended info attributes for this channel.
  *			The array is NULL terminated, the last element should
  *			have its name field set to NULL.
+ * @parent:		Optional pointer to the parent channel spec for
+ *			hierarchical channel relationships. When set, a read-only
+ *			"parent" sysfs attribute is created containing the
+ *			parent channel's sysfs name prefix (e.g. "in_voltage0").
  * @extend_name:	Allows labeling of channel attributes with an
  *			informative name. Note this has no effect codes etc,
  *			unlike modifiers.
@@ -309,6 +313,7 @@ struct iio_chan_spec {
 	const struct iio_event_spec *event_spec;
 	unsigned int		num_event_specs;
 	const struct iio_chan_spec_ext_info *ext_info;
+	const struct iio_chan_spec *parent;
 	const char		*extend_name;
 	const char		*datasheet_name;
 	unsigned int		modified:1;

-- 
2.43.0