On Sun, 2013-07-21 at 08:05 +0000, Chaiken, Alison wrote: > David Woodhouse <dw...@infradead.org> wrote: > >> I've heard tales of people having to keep device-tree files for their > >> board tightly in sync with the specific *version* of the Linux kernel > >> that they were shipped with. > > Assuredly if in a kernel update a driver adds new features which are > enabled by new properties described in the device-tree, updating both > the kernel and the device-tree at the same time makes sense?
Let me check I understand you correctly... In this scenario, the old kernel's driver simply didn't *use* the feature which was already (optionally) present. The later kernel *does* use the feature, and thus it needs to be described properly? If so, that means the initial device-tree binding was *WRONG*. It omitted the description of this hardware feature, purely because the Linux driver at the time didn't happen to use it. Violating the cardinal rule that the device-tree description of the hardware SHALL NOT be dependent on any OS-specifics. It should describe the hardware. And it didn't. And even in this scenario, although the initial author of the device-tree binding should of course be whipped for the omission of the feature in question, there should be no reason why we cannot simply use the *newer* device-tree in all circumstances. The older driver which doesn't use the optional feature should still work — just without *using* that feature, of course. If you ever encounter a scenario where you can't just use the latest device-tree, and an older kernel requires that you ship a contemporary device-tree to match it, then something has gone *catastrophically* wrong. I think it's definitely worth having a session on device-tree bindings, to ensure that this subject is properly understood. I would be keen to attend that. -- dwmw2
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