[PATCH v2] checkpatch: add support for Assisted-by tag

[Sasha Levin <sashal@kernel.org>]

The Assisted-by tag was introduced in
Documentation/process/coding-assistants.rst for attributing AI tool
contributions to kernel patches. However, checkpatch.pl did not
recognize this tag, causing two issues:

  WARNING: Non-standard signature: Assisted-by:
  ERROR: Unrecognized email address: 'AGENT_NAME:MODEL_VERSION'

Fix this by:
1. Adding Assisted-by to the recognized $signature_tags list
2. Skipping email validation for Assisted-by lines since they use the
   AGENT_NAME:MODEL_VERSION format instead of an email address
3. Warning when the Assisted-by value doesn't match the expected format

Reported-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Changes from v1:
 - Use next instead of wrapping the email validation block in an else
   clause, as suggested by Joe Perches.

 scripts/checkpatch.pl | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index e56374662ff79..27a43a4d9c438 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -641,6 +641,7 @@ our $signature_tags = qr{(?xi:
 	Reviewed-by:|
 	Reported-by:|
 	Suggested-by:|
+	Assisted-by:|
 	To:|
 	Cc:
 )};
@@ -3105,6 +3106,15 @@ sub process {
 				}
 			}
 
+			# Assisted-by uses AGENT_NAME:MODEL_VERSION format, not email
+			if ($sign_off =~ /^Assisted-by:/i) {
+				if ($email !~ /^\S+:\S+/) {
+					WARN("BAD_SIGN_OFF",
+					     "Assisted-by expects 'AGENT_NAME:MODEL_VERSION [TOOL1] [TOOL2]' format\n" . $herecurr);
+				}
+				next;
+			}
+
 			my ($email_name, $name_comment, $email_address, $comment) = parse_email($email);
 			my $suggested_email = format_email(($email_name, $name_comment, $email_address, $comment));
 			if ($suggested_email eq "") {
-- 
2.51.0