[Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?]
From: Grant Likely <hidden>
Date: 2013-07-30 04:35:26
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On Mon, Jul 29, 2013 at 1:31 AM, Maxime Ripard [off-list ref] wrote:
Hi, On Sun, Jul 28, 2013 at 03:19:03PM +0200, Richard Cochran wrote:quoted
On Sun, Jul 28, 2013 at 11:12:53AM +0200, Tomasz Figa wrote:quoted
I'm not really sure what effect on users this has. Maybe you should define "users"....quoted
Care to explain this reasoning?Use Case ~~~~~~~~ User acquires a machine running ARM Linux version 3.x, with u-boot and dtb in a read only flash partition. The board boots and works just fine. However, for his application, the user requires a new kernel feature that appeared in version 3.y where y > x. He compiles the new kernel, and it also works.I'm afraid this kind of use case will never be properly supported, DT stable ABI or not.
Why? New kernel features should be no problem at all. New driver features /might/ not be available, but only if the new feature requires additional data that isn't present in the tree and cannot be obtained elsewhere.
Think about this: what kernel will actually be shipped in that board? Most likely, it will be a BSP kernel from the vendor. Does the vendor will have made that commitment to have a stable ABI for the DT? Will it use the same bindings than mainline? Do we want to support all the crazy bindings every vendor will come up with?
That's not a DT issue. That an out-of-tree board/SoC support issue. DT doesn't make that any better or worse. g.