[PATCH v4] LICENSES: Explicitly allow SPDX-FileCopyrightText

[Krzysztof Kozlowski]

Sources already have SPDX-FileCopyrightText (~40 instances) and more
appear on the mailing list, so document that it is allowed.  On the
other hand SPDX defines several other tags like SPDX-FileType, so add
checkpatch rule to narrow desired tags only to two of them - license and
copyright.  That way no new tags would sneak in to the kernel unnoticed.

Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>
---

Other way would be to remove SPDX-FileCopyrightText from existing files
and disallow this, but one way or another we should be explicit about
it.  Otherwise people will be sending more of these and each maintainer
would need to make their own call.

Changes in v4:
1. Grammar - "unsupported" -> "disallowed"
2. Add tag

Changes in v3:
1. Typo "or multiple"

Changes in v2:
1. Doc adjustments based on feedback from Greg and Laurent.
2. "unused" -> "unsupported"
3. Drop redundant blank line
---
 Documentation/process/license-rules.rst | 7 +++++--
 scripts/checkpatch.pl                   | 8 ++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/Documentation/process/license-rules.rst b/Documentation/process/license-rules.rst
index 59a7832df7d0..b0176bb8a465 100644
--- a/Documentation/process/license-rules.rst
+++ b/Documentation/process/license-rules.rst
@@ -63,8 +63,11 @@ License identifier syntax
    The SPDX license identifier in kernel files shall be added at the first
    possible line in a file which can contain a comment.  For the majority
    of files this is the first line, except for scripts which require the
-   '#!PATH_TO_INTERPRETER' in the first line.  For those scripts the SPDX
-   identifier goes into the second line.
+   '#!PATH_TO_INTERPRETER' in the first line.  For those scripts, the SPDX
+   license identifier goes into the second line.
+
+   The license identifier line can then be followed by one or multiple
+   SPDX-FileCopyrightText lines if desired.
 
 |
 
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index bec7930cdd66..c0025d2f5741 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3856,6 +3856,14 @@ sub process {
 			     "Misplaced SPDX-License-Identifier tag - use line $checklicenseline instead\n" . $herecurr);
 		}
 
+# check for disallowed SPDX file tags
+		if ($rawline =~ /\bSPDX-.*:/ &&
+		    $rawline !~ /\bSPDX-License-Identifier:/ &&
+		    $rawline !~ /\bSPDX-FileCopyrightText:/) {
+			WARN("SPDX_LICENSE_TAG",
+			     "Disallowed SPDX tag\n" . $herecurr);
+		}
+
 # line length limit (with some exclusions)
 #
 # There are a few types of lines that may extend beyond $max_line_length:
-- 
2.51.0