1.. SPDX-License-Identifier: GPL-2.0
2
3===================
4Devicetree (DT) ABI
5===================
6
7I. Regarding stable bindings/ABI, we quote from the 2013 ARM mini-summit
8   summary document:
9
10     "That still leaves the question of, what does a stable binding look
11     like?  Certainly a stable binding means that a newer kernel will not
12     break on an older device tree, but that doesn't mean the binding is
13     frozen for all time. Grant said there are ways to change bindings that
14     don't result in breakage. For instance, if a new property is added,
15     then default to the previous behaviour if it is missing. If a binding
16     truly needs an incompatible change, then change the compatible string
17     at the same time.  The driver can bind against both the old and the
18     new. These guidelines aren't new, but they desperately need to be
19     documented."
20
21II.  General binding rules
22
23  1) Maintainers, don't let perfect be the enemy of good.  Don't hold up a
24     binding because it isn't perfect.
25
26  2) Use specific compatible strings so that if we need to add a feature (DMA)
27     in the future, we can create a new compatible string.  See I.
28
29  3) Bindings can be augmented, but the driver shouldn't break when given
30     the old binding. ie. add additional properties, but don't change the
31     meaning of an existing property. For drivers, default to the original
32     behaviour when a newly added property is missing.
33
34  4) Don't submit bindings for staging or unstable.  That will be decided by
35     the devicetree maintainers *after* discussion on the mailinglist.
36
37III. Notes
38
39  1) This document is intended as a general familiarization with the process as
40     decided at the 2013 Kernel Summit.  When in doubt, the current word of the
41     devicetree maintainers overrules this document.  In that situation, a patch
42     updating this document would be appreciated.
43