[PATCH] checkpatch: prevent reporting C99_COMMENTS error for SPDX tag in .c file

[Quentin Monnet <quentin@isovalent.com>]

When checkpatch.pl is invoked with "--ignore C99_COMMENT_TOLERANCE", it
reports C99-style comments found in the code, by matching on the
double-slash pattern "//". This includes the leading slashes before the
SPDX tags that are now used in a majority of C files.

Such tags are commented with the double-slash on purpose, and should not
trigger errors from checkpatch. Let's ignore them when searching for
C99-style comments to report.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 scripts/checkpatch.pl | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 3cacc122c528..67f350c580ea 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3983,7 +3983,10 @@ sub process {
 		}
 
 # no C99 // comments
-		if ($line =~ m{//}) {
+		if ($line =~ m{//} &&
+		    !($rawline =~ m{// SPDX-License-Identifier:} &&
+		      $realfile =~ /\.c$/ &&
+		      $realline == $checklicenseline)) {
 			if (ERROR("C99_COMMENTS",
 				  "do not use C99 // comments\n" . $herecurr) &&
 			    $fix) {
-- 
2.20.1