checkpatch: check proper licensing of Devicetree bindings

According to Devicetree maintainers (see Link: below), the Devicetree
binding documents are preferrably licensed (GPL-2.0-only OR BSD-2-Clause).

Let's check that.  The actual check is a bit more relaxed, to allow more
liberal but compatible licensing (e.g.  GPL-2.0-or-later OR BSD-2-Clause).

Signed-off-by: Lubomir Rintel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Joe Perches <[email protected]>
Acked-by: Laurent Pinchart <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Neil Armstrong <[email protected]>
Cc: Laurent Pinchart <[email protected]>,
Cc: Jonas Karlman <[email protected]>,
Cc: Jernej Skrabec <[email protected]>,
Cc: Mark Rutland <[email protected]>,
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>,
Link: https://lore.kernel.org/lkml/20200108142132.GA4830@bogus/
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: lkundrak

scripts/checkpatch.pl

@@ -3157,6 +3157,17 @@ sub process {
 						WARN("SPDX_LICENSE_TAG",
 						     "'$spdx_license' is not supported in LICENSES/...\n" . $herecurr);
 					}
+					if ($realfile =~ m@^Documentation/devicetree/bindings/@ &&
+					    not $spdx_license =~ /GPL-2\.0.*BSD-2-Clause/) {
+						my $msg_level = \&WARN;
+						$msg_level = \&CHK if ($file);
+						if (&{$msg_level}("SPDX_LICENSE_TAG",
+
+								  "DT binding documents should be licensed (GPL-2.0-only OR BSD-2-Clause)\n" . $herecurr) &&
+						    $fix) {
+							$fixed[$fixlinenr] =~ s/SPDX-License-Identifier: .*/SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)/;
+						}
+					}
 				}
 			}
 		}