Documentation/devicetree/bindings/ABI.txt

   1
   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.