[PATCH v6 02/10] property: Add functions to iterate named child

Matti Vaittinen
2025-03-10T12:56:03Z

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There are a few use-cases where child nodes with a specific name need to
be parsed. Code like:

fwnode_for_each_child_node()
if (fwnode_name_eq())
...

can be found from a various drivers/subsystems. Adding a macro for this
can simplify things a bit.

In a few cases the data from the found nodes is later added to an array,
which is allocated based on the number of found nodes. One example of
such use is the IIO subsystem's ADC channel nodes, where the relevant
nodes are named as channel[@N].

Add a helpers for iterating and counting device's sub-nodes with certain
name instead, of open-coding this in every user.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
Revision history:
v5 => v6:
- Add helpers to also iterate through the nodes.
v4 => v5:
- Use given name instead of string 'channel' when counting the nodes
- Add also fwnode_get_child_node_count_named() as suggested by Rob.
v3 => v4:
- New patch as suggested by Jonathan, see discussion in:
https://lore.kernel.org/lkml/20250223161338.5c896280@jic23-huawei/

Please note, the checkpatch.pl was not happy about the for_each...()
macros. I tried to make them to follow the existing convention. I am
open to suggestions how to improve.

---
drivers/base/property.c | 54 ++++++++++++++++++++++++++++++++++++++++
include/linux/property.h | 20 +++++++++++++++
2 files changed, 74 insertions(+)

diff --git a/drivers/base/property.c b/drivers/base/property.c
index c1392743df9c..335262a894f4 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -945,6 +945,60 @@ unsigned int device_get_child_node_count(const struct device *dev)
}
EXPORT_SYMBOL_GPL(device_get_child_node_count);

+/**
+ * fwnode_get_named_child_node_count - number of child nodes with given name
+ * @fwnode: Node which child nodes are counted.
+ * @name: String to match child node name against.
+ *
+ * Scan child nodes and count all the nodes with a specific name. Return the
+ * number of found nodes. Potential '@number' -ending for scanned names is
+ * ignored. Eg,
+ * device_get_child_node_count(dev, "channel");
+ * would match all the nodes:
+ * channel { }, channel@0 {}, channel@0xabba {}...
+ *
+ * Return: the number of child nodes with a matching name for a given device.
+ */
+unsigned int fwnode_get_named_child_node_count(const struct fwnode_handle *fwnode,
+ const char *name)
+{
+ struct fwnode_handle *child;
+ unsigned int count = 0;
+
+ fwnode_for_each_named_child_node(fwnode, child, name)
+ count++;
+
+ return count;
+}
+EXPORT_SYMBOL_GPL(fwnode_get_named_child_node_count);
+
+/**
+ * device_get_named_child_node_count - number of child nodes with given name
+ * @dev: Device to count the child nodes for.
+ * @name: String to match child node name against.
+ *
+ * Scan device's child nodes and find all the nodes with a specific name and
+ * return the number of found nodes. Potential '@number' -ending for scanned
+ * names is ignored. Eg,
+ * device_get_child_node_count(dev, "channel");
+ * would match all the nodes:
+ * channel { }, channel@0 {}, channel@0xabba {}...
+ *
+ * Return: the number of child nodes with a matching name for a given device.
+ */
+unsigned int device_get_named_child_node_count(const struct device *dev,
+ const char *name)
+{
+ struct fwnode_handle *child;
+ unsigned int count = 0;
+
+ device_for_each_named_child_node(dev, child, name)
+ count++;
+
+ return count;
+}
+EXPORT_SYMBOL_GPL(device_get_named_child_node_count);
+
bool device_dma_supported(const struct device *dev)
{
return fwnode_call_bool_op(dev_fwnode(dev), device_dma_supported);
diff --git a/include/linux/property.h b/include/linux/property.h
index e214ecd241eb..6dd9ae83e9a5 100644
--- a/include/linux/property.h
+++ b/include/linux/property.h
@@ -167,10 +167,18 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
for (child = fwnode_get_next_child_node(fwnode, NULL); child; \
child = fwnode_get_next_child_node(fwnode, child))

+#define fwnode_for_each_named_child_node(fwnode, child, name) \
+ fwnode_for_each_child_node(fwnode, child) \
+ if (!fwnode_name_eq(child, name)) { } else
+
#define fwnode_for_each_available_child_node(fwnode, child) \
for (child = fwnode_get_next_available_child_node(fwnode, NULL); child;\
child = fwnode_get_next_available_child_node(fwnode, child))

+#define fwnode_for_each_available_named_child_node(fwnode, child, name) \
+ fwnode_for_each_available_child_node(fwnode, child) \
+ if (!fwnode_name_eq(child, name)) { } else
+
struct fwnode_handle *device_get_next_child_node(const struct device *dev,
struct fwnode_handle *child);

@@ -178,11 +186,19 @@ struct fwnode_handle *device_get_next_child_node(const struct device *dev,
for (child = device_get_next_child_node(dev, NULL); child; \
child = device_get_next_child_node(dev, child))

+#define device_for_each_named_child_node(dev, child, name) \
+ device_for_each_child_node(dev, child) \
+ if (!fwnode_name_eq(child, name)) { } else
+
#define device_for_each_child_node_scoped(dev, child) \
for (struct fwnode_handle *child __free(fwnode_handle) = \
device_get_next_child_node(dev, NULL); \
child; child = device_get_next_child_node(dev, child))

+#define device_for_each_named_child_node_scoped(dev, child, name) \
+ device_for_each_child_node_scoped(dev, child) \
+ if (!fwnode_name_eq(child, name)) { } else
+
struct fwnode_handle *fwnode_get_named_child_node(const struct fwnode_handle *fwnode,
const char *childname);
struct fwnode_handle *device_get_named_child_node(const struct device *dev,
@@ -209,6 +225,10 @@ int fwnode_irq_get(const struct fwnode_handle *fwnode, unsigned int index);
int fwnode_irq_get_byname(const struct fwnode_handle *fwnode, const char *name);

unsigned int device_get_child_node_count(const struct device *dev);
+unsigned int fwnode_get_named_child_node_count(const struct fwnode_handle *fwnode,
+ const char *name);
+unsigned int device_get_named_child_node_count(const struct device *dev,
+ const char *name);

static inline int device_property_read_u8(const struct device *dev,
const char *propname, u8 *val)
--
2.48.1

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