samples: rust: platform: Add property child and reference args examples

Add some example usage of the device property methods for reading
DT/ACPI/swnode child nodes and reference args.

Signed-off-by: Remo Senekowitsch <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[ Convert 'child@{0,1}' to 'child-{0,1}'; skip child nodes without
'compatible' property in of_unittest_platform_populate() as proposed
by Rob Herring. - Danilo]
Signed-off-by: Danilo Krummrich <[e-mail]>

drivers/of/unittest-data/tests-platform.dtsi

···
 
 				test,u32-prop = <0xdeadbeef>;
 				test,i16-array = /bits/ 16 <1 2 (-3) (-4)>;
+
+				ref_child_0: child-0 {
+					test,ref-arg = <&ref_child_1 0x20 0x32>;
+				};
+				ref_child_1: child-1 {
+					test,ref-arg = <&ref_child_0 0x10 0x64>;
+				};
 			};
 		};
 

drivers/of/unittest.c

···
 	of_platform_populate(np, match, NULL, &test_bus->dev);
 	for_each_child_of_node(np, child) {
 		for_each_child_of_node(child, grandchild) {
+			if (!of_property_present(grandchild, "compatible"))
+				continue;
 			pdev = of_find_device_by_node(grandchild);
 			unittest(pdev,
 				 "Could not create device for node '%pOFn'\n",

samples/rust/rust_driver_platform.rs

···
 
 use kernel::{
     c_str,
-    device::{self, Core},
+    device::{
+        self,
+        property::{FwNodeReferenceArgs, NArgs},
+        Core,
+    },
     of, platform,
     prelude::*,
     str::CString,
···
         let name = c_str!("test,i16-array");
         let prop: KVec<i16> = fwnode.property_read_array_vec(name, 4)?.required_by(dev)?;
         dev_info!(dev, "'{name}'='{prop:?}' (KVec)\n");
+
+        for child in fwnode.children() {
+            let name = c_str!("test,ref-arg");
+            let nargs = NArgs::N(2);
+            let prop: FwNodeReferenceArgs = child.property_get_reference_args(name, nargs, 0)?;
+            dev_info!(dev, "'{name}'='{prop:?}'\n");
+        }
 
         Ok(())
     }