1 Licensing and contribution policy of dtc and libfdt

     2 ===================================================

     3 

     4 This dtc package contains two pieces of software: dtc itself, and

     5 libfdt which comprises the files in the libfdt/ subdirectory.  These

     6 two pieces of software, although closely related, are quite distinct.

     7 dtc does not incoporate or rely on libfdt for its operation, nor vice

     8 versa.  It is important that these two pieces of software have

     9 different license conditions.

    10 

    11 As the copyright banners in each source file attest, dtc is licensed

    12 under the GNU GPL.  The full text of the GPL can be found in the file

    13 entitled 'GPL' which should be included in this package.  dtc code,

    14 therefore, may not be incorporated into works which do not have a GPL

    15 compatible license.

    16 

    17 libfdt, however, is GPL/BSD dual-licensed.  That is, it may be used

    18 either under the terms of the GPL, or under the terms of the 2-clause

    19 BSD license (aka the ISC license).  The full terms of that license are

    20 given in the copyright banners of each of the libfdt source files.

    21 This is, in practice, equivalent to being BSD licensed, since the

    22 terms of the BSD license are strictly more permissive than the GPL.

    23 

    24 I made the decision to license libfdt in this way because I want to

    25 encourage widespread and correct usage of flattened device trees,

    26 including by proprietary or otherwise GPL-incompatible firmware or

    27 tools.  Allowing libfdt to be used under the terms of the BSD license

    28 makes that it easier for vendors or authors of such software to do so.

    29 

    30 This does mean that libfdt code could be "stolen" - say, included in a

    31 proprietary fimware and extended without contributing those extensions

    32 back to the libfdt mainline.  While I hope that doesn't happen, I

    33 believe the goal of allowing libfdt to be widely used is more

    34 important than avoiding that.  libfdt is quite small, and hardly

    35 rocket science; so the incentive for such impolite behaviour is small,

    36 and the inconvenience caused therby is not dire.

    37 

    38 Licenses such as the LGPL which would allow code to be used in non-GPL

    39 software, but also require contributions to be returned were

    40 considered.  However, libfdt is designed to be used in firmwares and

    41 other environments with unusual technical constraints.  It's difficult

    42 to anticipate all possible changes which might be needed to meld

    43 libfdt into such environments and so difficult to suitably word a

    44 license that puts the boundary between what is and isn't permitted in

    45 the intended place.  Again, I judged encouraging widespread use of

    46 libfdt by keeping the license terms simple and familiar to be the more

    47 important goal.

    48 

    49 **IMPORTANT** It's intended that all of libfdt as released remain

    50 permissively licensed this way.  Therefore only contributions which

    51 are released under these terms can be merged into the libfdt mainline.

    52 

    53 

    54 David Gibson <david@gibson.dropbear.id.au>

    55 (principal original author of dtc and libfdt)

    56 2 November 2007