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