checkpatch: add new warnings to author signoff checks.

index 31624bbb342e..e81f0bebbeb9 100755
@@ -2347,6 +2347,7 @@ sub process {
 	my $signoff = 0;
 	my $author = '';
 	my $authorsignoff = 0;
+	my $author_sob = '';
 	my $is_patch = 0;
 	my $is_binding_patch = -1;
 	my $in_header_lines = $file ? 0 : 1;

@@ -2674,9 +2675,34 @@ sub process {
 		if ($line =~ /^\s*signed-off-by:\s*(.*)/i) {
 			$signoff++;
 			$in_commit_log = 0;
-			if ($author ne '') {
+			if ($author ne ''  && $authorsignoff != 1) {
 				if (same_email_addresses($1, $author)) {
 					$authorsignoff = 1;
+				} else {
+					my $ctx = $1;
+					my ($email_name, $email_comment, $email_address, $comment1) = parse_email($ctx);
+					my ($author_name, $author_comment, $author_address, $comment2) = parse_email($author);
+
+					if ($email_address eq $author_address) {
+						$author_sob = $ctx;
+						$authorsignoff = 2;
+					} elsif ($email_name eq $author_name) {
+						$author_sob = $ctx;
+						$authorsignoff = 3;
+
+						my $address1 = $email_address;
+						my $address2 = $author_address;
+
+						if ($address1 =~ /(\S+)\+\S+(\@.*)/) {
+							$address1 = "$1$2";
+						}
+						if ($address2 =~ /(\S+)\+\S+(\@.*)/) {
+							$address2 = "$1$2";
+						}
+						if ($address1 eq $address2) {
+							$authorsignoff = 4;
+						}
+					}
 				}
 			}
 		}

@@ -6891,9 +6917,29 @@ sub process {
 		if ($signoff == 0) {
 			ERROR("MISSING_SIGN_OFF",
 			      "Missing Signed-off-by: line(s)\n");
-		} elsif (!$authorsignoff) {
-			WARN("NO_AUTHOR_SIGN_OFF",
-			     "Missing Signed-off-by: line by nominal patch author '$author'\n");
+		} elsif ($authorsignoff != 1) {
+			# authorsignoff values:
+			# 0 -> missing sign off
+			# 1 -> sign off identical
+			# 2 -> addresses match, names different
+			# 3 -> names match, addresses different
+			# 4 -> names match, addresses excluding subaddress details (refer RFC 5233) match
+
+			my $sob_msg = "'From: $author' != 'Signed-off-by: $author_sob'";
+
+			if ($authorsignoff == 0) {
+				ERROR("NO_AUTHOR_SIGN_OFF",
+				      "Missing Signed-off-by: line by nominal patch author '$author'\n");
+			} elsif ($authorsignoff == 2) {
+				WARN("NO_AUTHOR_SIGN_OFF",
+				     "From:/Signed-off-by: email name mismatch: $sob_msg\n");
+			} elsif ($authorsignoff == 3) {
+				WARN("NO_AUTHOR_SIGN_OFF",
+				     "From:/Signed-off-by: email address mismatch: $sob_msg\n");
+			} elsif ($authorsignoff == 4) {
+				WARN("NO_AUTHOR_SIGN_OFF",
+				     "From:/Signed-off-by: email extension mismatch: $sob_msg\n");
+			}
 		}
 	}