checkpatch: warn about using CONFIG_EXPERIMENTAL

This config item has not carried much meaning for a while now and is
almost always enabled by default.  As agreed during the Linux kernel
summit, it is being removed.  This will discourage future addition of
CONFIG_EXPERIMENTAL while it is being phased out.
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Whitcroft <apw@canonical.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

@@ -1757,6 +1757,13 @@ sub process {
 			#print "is_start<$is_start> is_end<$is_end> length<$length>\n";
 		}
 
+# discourage the addition of CONFIG_EXPERIMENTAL in Kconfig.
+		if ($realfile =~ /Kconfig/ &&
+		    $line =~ /.\s*depends on\s+.*\bEXPERIMENTAL\b/) {
+			WARN("CONFIG_EXPERIMENTAL",
+			     "Use of CONFIG_EXPERIMENTAL is deprecated. For alternatives, see https://lkml.org/lkml/2012/10/23/580\n");
+		}
+
 		if (($realfile =~ /Makefile.*/ || $realfile =~ /Kbuild.*/) &&
 		    ($line =~ /\+(EXTRA_[A-Z]+FLAGS).*/)) {
 			my $flag = $1;
@@ -1912,6 +1919,12 @@ sub process {
 # check we are in a valid C source file if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c)$/);
 
+# discourage the addition of CONFIG_EXPERIMENTAL in #if(def).
+		if ($line =~ /^\+\s*\#\s*if.*\bCONFIG_EXPERIMENTAL\b/) {
+			WARN("CONFIG_EXPERIMENTAL",
+			     "Use of CONFIG_EXPERIMENTAL is deprecated. For alternatives, see https://lkml.org/lkml/2012/10/23/580\n");
+		}
+
 # check for RCS/CVS revision markers
 		if ($rawline =~ /^\+.*\$(Revision|Log|Id)(?:\$|)/) {
 			WARN("CVS_KEYWORD",