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