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2a9330010b
Add some guidance documentation about what to do with device tree bindings and how ABI stability is to be handled. Signed-off-by: Jason Cooper <jason@lakedaemon.net> [grant.likely: added some clarification on subsystem binding rules] Signed-off-by: Grant Likely <grant.likely@linaro.org>
40 lines
1.8 KiB
Plaintext
40 lines
1.8 KiB
Plaintext
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Devicetree (DT) ABI
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I. Regarding stable bindings/ABI, we quote from the 2013 ARM mini-summit
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summary document:
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"That still leaves the question of, what does a stable binding look
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like? Certainly a stable binding means that a newer kernel will not
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break on an older device tree, but that doesn't mean the binding is
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frozen for all time. Grant said there are ways to change bindings that
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don't result in breakage. For instance, if a new property is added,
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then default to the previous behaviour if it is missing. If a binding
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truly needs an incompatible change, then change the compatible string
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at the same time. The driver can bind against both the old and the
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new. These guidelines aren't new, but they desperately need to be
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documented."
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II. General binding rules
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1) Maintainers, don't let perfect be the enemy of good. Don't hold up a
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binding because it isn't perfect.
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2) Use specific compatible strings so that if we need to add a feature (DMA)
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in the future, we can create a new compatible string. See I.
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3) Bindings can be augmented, but the driver shouldn't break when given
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the old binding. ie. add additional properties, but don't change the
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meaning of an existing property. For drivers, default to the original
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behaviour when a newly added property is missing.
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4) Don't submit bindings for staging or unstable. That will be decided by
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the devicetree maintainers *after* discussion on the mailinglist.
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III. Notes
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1) This document is intended as a general familiarization with the process as
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decided at the 2013 Kernel Summit. When in doubt, the current word of the
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devicetree maintainers overrules this document. In that situation, a patch
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updating this document would be appreciated.
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