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0001 Licensing and contribution policy of dtc and libfdt
0002 ===================================================
0003
0004 This dtc package contains two pieces of software: dtc itself, and
0005 libfdt which comprises the files in the libfdt/ subdirectory. These
0006 two pieces of software, although closely related, are quite distinct.
0007 dtc does not incoporate or rely on libfdt for its operation, nor vice
0008 versa. It is important that these two pieces of software have
0009 different license conditions.
0010
0011 As the copyright banners in each source file attest, dtc is licensed
0012 under the GNU GPL. The full text of the GPL can be found in the file
0013 entitled 'GPL' which should be included in this package. dtc code,
0014 therefore, may not be incorporated into works which do not have a GPL
0015 compatible license.
0016
0017 libfdt, however, is GPL/BSD dual-licensed. That is, it may be used
0018 either under the terms of the GPL, or under the terms of the 2-clause
0019 BSD license (aka the ISC license). The full terms of that license are
0020 given in the copyright banners of each of the libfdt source files.
0021 This is, in practice, equivalent to being BSD licensed, since the
0022 terms of the BSD license are strictly more permissive than the GPL.
0023
0024 I made the decision to license libfdt in this way because I want to
0025 encourage widespread and correct usage of flattened device trees,
0026 including by proprietary or otherwise GPL-incompatible firmware or
0027 tools. Allowing libfdt to be used under the terms of the BSD license
0028 makes that it easier for vendors or authors of such software to do so.
0029
0030 This does mean that libfdt code could be "stolen" - say, included in a
0031 proprietary fimware and extended without contributing those extensions
0032 back to the libfdt mainline. While I hope that doesn't happen, I
0033 believe the goal of allowing libfdt to be widely used is more
0034 important than avoiding that. libfdt is quite small, and hardly
0035 rocket science; so the incentive for such impolite behaviour is small,
0036 and the inconvenience caused therby is not dire.
0037
0038 Licenses such as the LGPL which would allow code to be used in non-GPL
0039 software, but also require contributions to be returned were
0040 considered. However, libfdt is designed to be used in firmwares and
0041 other environments with unusual technical constraints. It's difficult
0042 to anticipate all possible changes which might be needed to meld
0043 libfdt into such environments and so difficult to suitably word a
0044 license that puts the boundary between what is and isn't permitted in
0045 the intended place. Again, I judged encouraging widespread use of
0046 libfdt by keeping the license terms simple and familiar to be the more
0047 important goal.
0048
0049 **IMPORTANT** It's intended that all of libfdt as released remain
0050 permissively licensed this way. Therefore only contributions which
0051 are released under these terms can be merged into the libfdt mainline.
0052
0053
0054 David Gibson <david@gibson.dropbear.id.au>
0055 (principal original author of dtc and libfdt)
0056 2 November 2007
