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