LICENSES: Explicitly allow SPDX-FileCopyrightText

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

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.
 
 |
 

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: