dt/bindings: submitting patches and ABI documents

  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.

  Submitting devicetree (DT) binding patches

I. For patch submitters

  0) Normal patch submission rules from Documentation/SubmittingPatches

     applies.

  1) The Documentation/ portion of the patch should be a separate patch.

  2) Submit the entire series to the devicetree mailinglist at

       devicetree@vger.kernel.org

II. For kernel maintainers

  1) If you aren't comfortable reviewing a given binding, reply to it and ask

     the devicetree maintainers for guidance.  This will help them prioritize

     which ones to review and which ones are ok to let go.

  2) For driver (not subsystem) bindings: If you are comfortable with the

     binding, and it hasn't received an Acked-by from the devicetree

     maintainers after a few weeks, go ahead and take it.

     Subsystem bindings (anything affecting more than a single device)

     then getting a devicetree maintainer to review it is required.

  3) For a series going though multiple trees, the binding patch should be

     kept with the driver using the binding.

III. Notes

  0) Please see ...bindings/ABI.txt for details regarding devicetree ABI.

  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.