[PATCH v2 1/7] device property: add fwnode_property_read_string_index()

[Clément Léger]

Add fwnode_property_read_string_index() function which allows to
retrieve a string from an array by its index. This function is the
equivalent of of_property_read_string_index() but for fwnode support.
A .property_read_string_index callback is added to fwnode_ops to avoid
doing a full allocation of an array just to retrieve one value.

Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
---
 drivers/base/property.c  | 26 ++++++++++++++++++++++++++
 include/linux/fwnode.h   |  6 ++++++
 include/linux/property.h |  3 +++
 3 files changed, 35 insertions(+)

diff --git a/drivers/base/property.c b/drivers/base/property.c
index e6497f6877ee..a8dd6e496a1d 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -451,6 +451,32 @@ int fwnode_property_match_string(const struct fwnode_handle *fwnode,
 }
 EXPORT_SYMBOL_GPL(fwnode_property_match_string);
 
+/**
+ * fwnode_property_read_string_index - read a string in an array using an index
+ * @fwnode: Firmware node to get the property of
+ * @propname: Name of the property holding the array
+ * @index: Index of the string to look for
+ * @string: Pointer to the string if found
+ *
+ * Find a string by a given index in a string array and if it is found return
+ * the string value in @string.
+ *
+ * Return: %0 if the property was found (success),
+ *	   %-EINVAL if given arguments are not valid,
+ *	   %-ENODATA if the property does not have a value,
+ *	   %-EPROTO if the property is not an array of strings,
+ *	   %-ENXIO if no suitable firmware interface is present.
+ */
+int fwnode_property_read_string_index(const struct fwnode_handle *fwnode,
+				      const char *propname, int index,
+				      const char **string)
+{
+	return fwnode_call_int_op(fwnode, property_read_string_index, propname,
+				  index,
+				  string);
+}
+EXPORT_SYMBOL_GPL(fwnode_property_read_string_index);
+
 /**
  * fwnode_property_get_reference_args() - Find a reference with arguments
  * @fwnode:	Firmware node where to look for the reference
diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 3a532ba66f6c..71ba8f53cf1e 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -93,6 +93,9 @@ struct fwnode_reference_args {
  *			     success, a negative error code otherwise.
  * @property_read_string_array: Read an array of string properties. Return zero
  *				on success, a negative error code otherwise.
+ * @property_read_string_index: Read a string from a string array using an
+ *				index. Return zero on success, a negative error
+ *				code otherwise.
  * @get_name: Return the name of an fwnode.
  * @get_name_prefix: Get a prefix for a node (for printing purposes).
  * @get_parent: Return the parent of an fwnode.
@@ -123,6 +126,9 @@ struct fwnode_operations {
 	(*property_read_string_array)(const struct fwnode_handle *fwnode_handle,
 				      const char *propname, const char **val,
 				      size_t nval);
+	int (*property_read_string_index)(const struct fwnode_handle *fwnode,
+					  const char *propname, int index,
+					  const char **string);
 	const char *(*get_name)(const struct fwnode_handle *fwnode);
 	const char *(*get_name_prefix)(const struct fwnode_handle *fwnode);
 	struct fwnode_handle *(*get_parent)(const struct fwnode_handle *fwnode);
diff --git a/include/linux/property.h b/include/linux/property.h
index 7399a0b45f98..a033920eb10a 100644
--- a/include/linux/property.h
+++ b/include/linux/property.h
@@ -70,6 +70,9 @@ int fwnode_property_read_string_array(const struct fwnode_handle *fwnode,
 				      size_t nval);
 int fwnode_property_read_string(const struct fwnode_handle *fwnode,
 				const char *propname, const char **val);
+int fwnode_property_read_string_index(const struct fwnode_handle *fwnode,
+				      const char *propname, int index,
+				      const char **string);
 int fwnode_property_match_string(const struct fwnode_handle *fwnode,
 				 const char *propname, const char *string);
 int fwnode_property_get_reference_args(const struct fwnode_handle *fwnode,
-- 
2.34.1