checkpatch: add DT compatible string documentation checks

This adds a simple check that any compatible strings in DeviceTree dts
files are present in Documentation/devicetree/bindings.  Vendor prefixes
are also checked for existing in vendor-prefixes.txt These should be
temporary checks until we have more sophisticated binding schema
checking.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2040,6 +2040,33 @@ sub process {
 			     "Use of $flag is deprecated, please use \`$replacement->{$flag} instead.\n" . $herecurr) if ($replacement->{$flag});
 		}
 
+# check for DT compatible documentation
+		if (defined $root && $realfile =~ /\.dts/ &&
+		    $rawline =~ /^\+\s*compatible\s*=/) {
+			my @compats = $rawline =~ /\"([a-zA-Z0-9\-\,\.\+_]+)\"/g;
+
+			foreach my $compat (@compats) {
+				my $compat2 = $compat;
+				my $dt_path =  $root . "/Documentation/devicetree/bindings/";
+				$compat2 =~ s/\,[a-z]*\-/\,<\.\*>\-/;
+				`grep -Erq "$compat|$compat2" $dt_path`;
+				if ( $? >> 8 ) {
+					WARN("UNDOCUMENTED_DT_STRING",
+					     "DT compatible string \"$compat\" appears un-documented -- check $dt_path\n" . $herecurr);
+				}
+
+				my $vendor = $compat;
+				my $vendor_path = $dt_path . "vendor-prefixes.txt";
+				next if (! -f $vendor_path);
+				$vendor =~ s/^([a-zA-Z0-9]+)\,.*/$1/;
+				`grep -Eq "$vendor" $vendor_path`;
+				if ( $? >> 8 ) {
+					WARN("UNDOCUMENTED_DT_STRING",
+					     "DT compatible string vendor \"$vendor\" appears un-documented -- check $vendor_path\n" . $herecurr);
+				}
+			}
+		}
+
 # check we are in a valid source file if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|s|S|pl|sh)$/);