of: unittest: document intentional interrupt-map provider build warning

A recently implemented dtc compiler warning reports a dts problem
via a build warning:

   drivers/of/unittest-data/tests-interrupts.dtsi:32.26-35.6: Warning (interrupt_map): /testcase-data/interrupts/intmap1: Missing '#address-cells' in interrupt-map provider

The warning will be addressed by a separate patch by suppressing the
warning for .dts files that include this .dtsi.  This patch documents
why the warning is due to a deliberately incorrect .dtsi file so that
no one will fix the .dtsi file to prevent the build warning.

Signed-off-by: Frank Rowand <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rob Herring <[email protected]>

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

@@ -31,6 +31,21 @@
 
 			test_intmap1: intmap1 {
 				#interrupt-cells = <2>;
+				/*
+				 * #address-cells is required
+				 *
+				 * The property is not provided in this node to
+				 * test that the code will properly handle
+				 * this case for legacy .dts files.
+				 *
+				 * Not having #address-cells will result in a
+				 * warning from dtc starting with
+				 * version v1.6.1-19-g0a3a9d3449c8
+				 * The warning is suppressed by adding
+				 * -Wno-interrupt_map to the Makefile for all
+				 * .dts files this include this .dtsi
+				#address-cells = <1>;
+				 */
 				interrupt-map = <0x5000 1 2 &test_intc0 15>;
 			};
 
@@ -46,6 +61,10 @@
 
 			interrupts-extended0 {
 				reg = <0x5000 0x100>;
+				/*
+				 * Do not remove &test_intmap1 from this
+				 * property - see comment in node intmap1
+				 */
 				interrupts-extended = <&test_intc0 1>,
 						      <&test_intc1 2 3 4>,
 						      <&test_intc2 5 6>,

drivers/of/unittest.c

@@ -1129,6 +1129,12 @@ static void __init of_unittest_parse_interrupts_extended(void)
 			passed &= (args.args[1] == 14);
 			break;
 		case 6:
+			/*
+			 * Tests child node that is missing property
+			 * #address-cells.  See the comments in
+			 * drivers/of/unittest-data/tests-interrupts.dtsi
+			 * nodes intmap1 and interrupts-extended0
+			 */
 			passed &= !rc;
 			passed &= (args.args_count == 1);
 			passed &= (args.args[0] == 15);