checkpatch: Add a warning for pre-schema driver model tags

Help ensure that these don't creep into development by adding a check in
checkpatch for them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ccfcbb3..62b764f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2680,6 +2680,12 @@
 		"DEVICE_PRIV_AUTO", $herecurr);
 	u_boot_struct_name($line, "per_device_plat_auto", "_plat",
 		"DEVICE_PLAT_AUTO", $herecurr);
+
+	# Avoid using the pre-schema driver model tags
+	if ($line =~ /^\+.*u-boot,dm-.*/) {
+		ERROR("PRE_SCHEMA",
+		      "Driver model schema uses 'bootph-...' tags now\n" . $herecurr);
+	}
 }
 
 sub exclude_global_initialisers {
diff --git a/tools/patman/test_checkpatch.py b/tools/patman/test_checkpatch.py
index 4c2ab6e..a8bb364 100644
--- a/tools/patman/test_checkpatch.py
+++ b/tools/patman/test_checkpatch.py
@@ -452,6 +452,12 @@
         self.check_strl("cat");
         self.check_strl("cpy");
 
+    def test_schema(self):
+        """Check for uses of strn(cat|cpy)"""
+        pm = PatchMaker()
+        pm.add_line('arch/sandbox/dts/sandbox.dtsi', '\tu-boot,dm-pre-proper;')
+        self.check_single_message(pm, 'PRE_SCHEMA', 'error')
+
 if __name__ == "__main__":
     unittest.main()
     gitutil.RunTests()