[PATCH v2] LICENSES: Explicitly allow SPDX-FileCopyrightText

[Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>]

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@ideasonboard.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>

---

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 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..5cc58168e3d9 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 of multiple
+   SPDX-FileCopyrightText lines if desired.
 
 |
 
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 362a8d1cd327..cc2a5882fef8 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3844,6 +3844,14 @@ sub process {
 			     "Misplaced SPDX-License-Identifier tag - use line $checklicenseline instead\n" . $herecurr);
 		}
 
+# check for unsupported SPDX file tags
+		if ($rawline =~ /\bSPDX-.*:/ &&
+		    $rawline !~ /\bSPDX-License-Identifier:/ &&
+		    $rawline !~ /\bSPDX-FileCopyrightText:/) {
+			WARN("SPDX_LICENSE_TAG",
+			     "Unsupported 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