fdt: Introduce helper method fdt_overlay_apply_verbose()

Introduce fdt_overlay_apply_verbose, a method that applies an
overlay but in the case of an error produces a helpful message.

In addition if a base tree is found to be missing the __symbols__
node the message will point out that the probable reason is that
the base tree was miscompiled without the -@ option.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Acked-by: Simon Glass <sjg@chromium.org>

common/fdt_support.c

@@ -1655,3 +1655,34 @@ int fdt_fixup_display(void *blob, const char *path, const char *display)
 	}
 	return toff;
 }
+
+#ifdef CONFIG_OF_LIBFDT_OVERLAY
+/**
+ * fdt_overlay_apply_verbose - Apply an overlay with verbose error reporting
+ *
+ * @fdt: ptr to device tree
+ * @fdto: ptr to device tree overlay
+ *
+ * Convenience function to apply an overlay and display helpful messages
+ * in the case of an error
+ */
+int fdt_overlay_apply_verbose(void *fdt, void *fdto)
+{
+	int err;
+	bool has_symbols;
+
+	err = fdt_path_offset(fdt, "/__symbols__");
+	has_symbols = err >= 0;
+
+	err = fdt_overlay_apply(fdt, fdto);
+	if (err < 0) {
+		printf("failed on fdt_overlay_apply(): %s\n",
+				fdt_strerror(err));
+		if (!has_symbols) {
+			printf("base fdt does did not have a /__symbols__ node\n");
+			printf("make sure you've compiled with -@\n");
+		}
+	}
+	return err;
+}
+#endif

include/fdt_support.h

@@ -264,6 +264,8 @@ int arch_fixup_memory_node(void *blob);
 int fdt_setup_simplefb_node(void *fdt, int node, u64 base_address, u32 width,
 			    u32 height, u32 stride, const char *format);
 
+int fdt_overlay_apply_verbose(void *fdt, void *fdto);
+
 #endif /* ifdef CONFIG_OF_LIBFDT */
 
 #ifdef USE_HOSTCC