[PATCH 1/6] 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.

Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
---
 drivers/base/property.c  | 48 ++++++++++++++++++++++++++++++++++++++++
 include/linux/property.h |  3 +++
 2 files changed, 51 insertions(+)

diff --git a/drivers/base/property.c b/drivers/base/property.c
index e6497f6877ee..67c33c11f00c 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -451,6 +451,54 @@ 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)
+{
+	const char **values;
+	int nval, ret;
+
+	nval = fwnode_property_read_string_array(fwnode, propname, NULL, 0);
+	if (nval < 0)
+		return nval;
+
+	if (index >= nval)
+		return -EINVAL;
+
+	if (nval == 0)
+		return -ENODATA;
+
+	values = kcalloc(nval, sizeof(*values), GFP_KERNEL);
+	if (!values)
+		return -ENOMEM;
+
+	ret = fwnode_property_read_string_array(fwnode, propname, values, nval);
+	if (ret < 0)
+		goto out;
+
+	*string = values[index];
+out:
+	kfree(values);
+	return ret;
+}
+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/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