[PATCH v6 2/2] checkpatch: Add option to not force /* */ for SPDX

[Petr Vorel <pvorel@suse.cz>]

Add option --spdx-cxx-comments to not force C comments (/* */) for SPDX,
but allow also C++ comments (//).

As documented in aa19a176df95d6, this is required for some old
toolchains still have older assembler tools which cannot handle C++
style comments. This avoids forcing this for projects which vendored
checkpatch.pl (e.g. LTP or u-boot).

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
Changes in v6:
* Fix escaping '..' by \Q  \E (Simon, sashiko)
* Fix formatting of /* */ in Documentation/dev-tools/checkpatch.rst
(sashiko)
* Fix wording in the commit message (Simon)

Link to v5:
https://lore.kernel.org/lkml/20260417170346.448758-2-pvorel@suse.cz/

Link to v4:
https://lore.kernel.org/lkml/20260415143636.272605-2-pvorel@suse.cz/

Link to v3:
https://lore.kernel.org/lkml/20260408120603.54351-2-pvorel@suse.cz/

Thanks Simon for patient review, let's see if maintainers like the
changes.

 Documentation/dev-tools/checkpatch.rst |  7 +++++++
 scripts/checkpatch.pl                  | 23 ++++++++++++++++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index 010dfcd615afc..6139a08c34cd8 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -184,6 +184,13 @@ Available options:
    Override checking of perl version.  Runtime errors may be encountered after
    enabling this flag if the perl version does not meet the minimum specified.
 
+ - --spdx-cxx-comments
+
+   Don't force C comments ``/* */`` for SPDX license (required by old
+   toolchains), allow also C++ comments ``//``.
+
+   NOTE: it should *not* be used for Linux mainline.
+
  - --codespell
 
    Use the codespell dictionary for checking spelling errors.
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index d86f5ccb06fe4..18da0cbf873cb 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -61,6 +61,7 @@ my $def_configuration_dirs = ".:$ENV{HOME}:.scripts";
 my $env_config_dir = 'CHECKPATCH_CONFIG_DIR';
 my $max_line_length = 100;
 my $ignore_perl_version = 0;
+my $spdx_cxx_comments = 0;
 my $minimum_perl_version = 5.10.0;
 my $min_conf_desc_length = 4;
 my $spelling_file = "$D/spelling.txt";
@@ -137,6 +138,10 @@ Options:
                              file.  It's your fault if there's no backup or git
   --ignore-perl-version      override checking of perl version.  expect
                              runtime errors.
+  --spdx-cxx-comments        don't force C comments (/* */) for SPDX license
+                             (required by old toolchains), allow also C++
+                             comments (//).
+                             NOTE: it should *not* be used for Linux mainline.
   --codespell                Use the codespell dictionary for spelling/typos
                              (default:$codespellfile)
   --codespellfile            Use this codespell dictionary
@@ -346,6 +351,7 @@ GetOptions(
 	'fix!'		=> \$fix,
 	'fix-inplace!'	=> \$fix_inplace,
 	'ignore-perl-version!' => \$ignore_perl_version,
+	'spdx-cxx-comments!' => \$spdx_cxx_comments,
 	'debug=s'	=> \%debug,
 	'test-only=s'	=> \$tst_only,
 	'codespell!'	=> \$codespell,
@@ -3814,26 +3820,33 @@ sub process {
 				$checklicenseline = 2;
 			} elsif ($rawline =~ /^\+/) {
 				my $comment = "";
-				if ($realfile =~ /\.(h|s|S)$/) {
-					$comment = '/*';
-				} elsif ($realfile =~ /\.(c|rs|dts|dtsi)$/) {
+				if ($realfile =~ /\.(c|rs|dts|dtsi)$/) {
 					$comment = '//';
 				} elsif (($checklicenseline == 2) || $realfile =~ /\.(sh|pl|py|awk|tc|yaml)$/) {
 					$comment = '#';
 				} elsif ($realfile =~ /\.rst$/) {
 					$comment = '..';
 				}
+				my $pattern = qr{\Q$comment\E};
+				if ($realfile =~ /\.(h|s|S)$/) {
+					$comment = '/*';
+					$pattern = qr{/\*};
+					if ($spdx_cxx_comments) {
+						$comment = '// or /*';
+						$pattern = qr{//|/\*};
+					}
+				}
 
 # check SPDX comment style for .[chsS] files
 				if ($realfile =~ /\.[chsS]$/ &&
 				    $rawline =~ /SPDX-License-Identifier:/ &&
-				    $rawline !~ m@^\+\s*\Q$comment\E\s*@) {
+				    $rawline !~ m@^\+\s*$pattern\s*@) {
 					WARN("SPDX_LICENSE_TAG",
 					     "Improper SPDX comment style for '$realfile', please use '$comment' instead\n" . $herecurr);
 				}
 
 				if ($comment !~ /^$/ &&
-				    $rawline !~ m@^\+\Q$comment\E SPDX-License-Identifier: @) {
+				    $rawline !~ m@^\+$pattern SPDX-License-Identifier: @) {
 					WARN("SPDX_LICENSE_TAG",
 					     "Missing or malformed SPDX-License-Identifier tag in line $checklicenseline\n" . $herecurr);
 				} elsif ($rawline =~ /(SPDX-License-Identifier: .*)/) {
-- 
2.53.0