of: base: add of_parse_phandle_with_optional_args()

Add a new variant of the of_parse_phandle_with_args() which treats the
cells name as optional. If it's missing, it is assumed that the phandle
has no arguments.

Up until now, a nvmem node didn't have any arguments, so all the device
trees haven't any '#*-cells' property. But there is a need for an
additional argument for the phandle, for which we need a '#*-cells'
property. Therefore, we need to support nvmem nodes with and without
this property.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230206134356.839737-10-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/of.h b/include/linux/of.h
index 8b9f94386dc3ad5b00ad5e09807f5e3cc4ee461a..98c252d2d8512980e0eb2ae01d59feea10291933 100644 (file)
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -1008,6 +1008,31 @@ static inline int of_parse_phandle_with_fixed_args(const struct device_node *np,
                                            index, out_args);
 }
 
+/**
+ * of_parse_phandle_with_optional_args() - Find a node pointed by phandle in a list
+ * @np:                pointer to a device tree node containing a list
+ * @list_name: property name that contains a list
+ * @cells_name:        property name that specifies phandles' arguments count
+ * @index:     index of a phandle to parse out
+ * @out_args:  optional pointer to output arguments structure (will be filled)
+ *
+ * Same as of_parse_phandle_with_args() except that if the cells_name property
+ * is not found, cell_count of 0 is assumed.
+ *
+ * This is used to useful, if you have a phandle which didn't have arguments
+ * before and thus doesn't have a '#*-cells' property but is now migrated to
+ * having arguments while retaining backwards compatibility.
+ */
+static inline int of_parse_phandle_with_optional_args(const struct device_node *np,
+                                                     const char *list_name,
+                                                     const char *cells_name,
+                                                     int index,
+                                                     struct of_phandle_args *out_args)
+{
+       return __of_parse_phandle_with_args(np, list_name, cells_name,
+                                           0, index, out_args);
+}
+
 /**
  * of_property_count_u8_elems - Count the number of u8 elements in a property
  *