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Licenses/README: Update some style and add explicit license to the document

- Add an SPDX license tag to the file, saying it's GPL-2.0.
- From the Linux Kernel v4.17-rc4, import the "License identifier
  syntax" section as-is from Documentation/process/license-rules.rst
  and then change it to be clearer about examples from the Linux Kernel
  vs examples found in U-Boot, and when we're talking about U-Boot.

Signed-off-by: Tom Rini <trini@konsulko.com>
Tom Rini 4 years ago
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commit
d405dae374
1 changed files with 92 additions and 10 deletions
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      Licenses/README

+ 92 - 10
Licenses/README

@@ -1,3 +1,5 @@
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+SPDX-License-Identifier: GPL-2.0
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+
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   U-Boot is Free Software.  It is copyrighted by Wolfgang Denk and
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 many others who contributed code (see the actual source code and the
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 git commit messages for details).  You can redistribute U-Boot and/or
@@ -31,27 +33,107 @@ information, ...) which makes automatic processing a nightmare.
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 To make this easier, such license headers in the source files will be
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 replaced with a single line reference to Unique License Identifiers
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-as defined by the Linux Foundation's SPDX project [1].  For example,
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-in a source file the full "GPL v2.0 or later" header text will be
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-replaced by a single line:
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-
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-	SPDX-License-Identifier:	GPL-2.0+
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-
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-Ideally, the license terms of all files in the source tree should be
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-defined by such License Identifiers; in no case a file can contain
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-more than one such License Identifier list.
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+as defined by the Linux Foundation's SPDX project [1].
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 If a "SPDX-License-Identifier:" line references more than one Unique
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 License Identifier, then this means that the respective file can be
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 used under the terms of either of these licenses, i. e. with
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-	SPDX-License-Identifier:	GPL-2.0+	BSD-3-Clause
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+	SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause
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 you can choose between GPL-2.0+ and BSD-3-Clause licensing.
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 We use the SPDX Unique License Identifiers here; these are available
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 at [2].
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+License identifier syntax
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+-------------------------
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+
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+1. Placement:
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+
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+   The SPDX license identifier in U-Boot files shall be added at the first
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+   possible line in a file which can contain a comment.  For the majority
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+   or files this is the first line, except for scripts which require the
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+   '#!PATH_TO_INTERPRETER' in the first line.  For those scripts the SPDX
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+   identifier goes into the second line.
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+
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+|
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+
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+2. Style:
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+
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+   The SPDX license identifier is added in form of a comment.  The comment
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+   style depends on the file type::
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+
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+      C source:	// SPDX-License-Identifier: <SPDX License Expression>
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+      C header:	/* SPDX-License-Identifier: <SPDX License Expression> */
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+      ASM:	/* SPDX-License-Identifier: <SPDX License Expression> */
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+      scripts:	# SPDX-License-Identifier: <SPDX License Expression>
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+      .rst:	.. SPDX-License-Identifier: <SPDX License Expression>
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+      .dts{i}:	// SPDX-License-Identifier: <SPDX License Expression>
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+
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+   If a specific tool cannot handle the standard comment style, then the
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+   appropriate comment mechanism which the tool accepts shall be used. This
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+   is the reason for having the "/\* \*/" style comment in C header
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+   files. There was build breakage observed with generated .lds files where
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+   'ld' failed to parse the C++ comment. This has been fixed by now, but
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+   there are still older assembler tools which cannot handle C++ style
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+   comments.
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+
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+|
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+
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+3. Syntax:
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+
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+   A <SPDX License Expression> is either an SPDX short form license
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+   identifier found on the SPDX License List, or the combination of two
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+   SPDX short form license identifiers separated by "WITH" when a license
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+   exception applies. When multiple licenses apply, an expression consists
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+   of keywords "AND", "OR" separating sub-expressions and surrounded by
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+   "(", ")" .
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+
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+   License identifiers for licenses like [L]GPL with the 'or later' option
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+   are constructed by using a "+" for indicating the 'or later' option.::
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+
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+      // SPDX-License-Identifier: GPL-2.0+
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+      // SPDX-License-Identifier: LGPL-2.1+
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+
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+   WITH should be used when there is a modifier to a license needed.
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+   For example, the linux kernel UAPI files use the expression::
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+
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+      // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
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+      // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note
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+
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+   Other examples using WITH exceptions found in the linux kernel are::
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+
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+      // SPDX-License-Identifier: GPL-2.0 WITH mif-exception
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+      // SPDX-License-Identifier: GPL-2.0+ WITH GCC-exception-2.0
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+
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+   Exceptions can only be used with particular License identifiers. The
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+   valid License identifiers are listed in the tags of the exception text
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+   file.
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+
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+   OR should be used if the file is dual licensed and only one license is
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+   to be selected.  For example, some dtsi files are available under dual
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+   licenses::
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+
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+      // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
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+
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+   Examples from U-Boot for license expressions in dual licensed files::
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+
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+      // SPDX-License-Identifier: GPL-2.0 OR MIT
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+      // SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause
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+
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+   AND should be used if the file has multiple licenses whose terms all
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+   apply to use the file. For example, if code is inherited from another
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+   project and permission has been given to put it in U-Boot, but the
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+   original license terms need to remain in effect::
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+
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+      // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) AND MIT
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+
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+   Another other example where both sets of license terms need to be
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+   adhered to is::
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+
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+      // SPDX-License-Identifier: GPL-1.0+ AND LGPL-2.1+
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+
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 [1] http://spdx.org/
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 [2] http://spdx.org/licenses/
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