checkpatch: validate MODULE_LICENSE content

There is a well defined list of expected values for MODULE_LICENSE so warn
the user upon usage of unknown values.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -5626,6 +5626,24 @@ sub process {
 				}
 			}
 		}
+
+# validate content of MODULE_LICENSE against list from include/linux/module.h
+		if ($line =~ /\bMODULE_LICENSE\s*\(\s*($String)\s*\)/) {
+			my $extracted_string = get_quoted_string($line, $rawline);
+			my $valid_licenses = qr{
+						GPL|
+						GPL\ v2|
+						GPL\ and\ additional\ rights|
+						Dual\ BSD/GPL|
+						Dual\ MIT/GPL|
+						Dual\ MPL/GPL|
+						Proprietary
+					}x;
+			if ($extracted_string !~ /^"(?:$valid_licenses)"$/x) {
+				WARN("MODULE_LICENSE",
+				     "unknown module license " . $extracted_string . "\n" . $herecurr);
+			}
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on