On Thu, 14 Dec 2023 at 23:53, Tom Rini trini@konsulko.com wrote:
On Thu, Dec 14, 2023 at 03:53:11PM +0100, neil.armstrong@linaro.org wrote:
Hi,
On 14/12/2023 14:50, Sumit Garg wrote:
Prerquisite
s/Prerquisite/Prerequisite/
Ack.
This patch series requires devicetree-rebasing git repo to be added as a subtree to the main U-boot repo via:
$ git subtree add --prefix devicetree-rebasing \ git://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git \ v6.6-dts --squash
So I think the big question is: when should the subtree be updated ?
Because as we discussed in the previous GH pull request, if a bindings changes was made in the upstream Linux DT, then the subtree update should wait until the u-boot support is merged before updating. This could cause a lot of frustration.
And this could cause a lot of regressions, even more if both Linux and U-boot are not maintained by the same people.
I think some of the important questions to ask are, how often / likely are the breakages to occur? It seems like these days it's either:
- U-Boot had an early version of the binding and we already state we don't support backwards compatibility here. It should be on the maintainer to be proactive in this case.
- It's a "the DT was wrong about the hardware, sorry not sorry it's an incompatible DTS change now". This too is hopefully the kind of thing that at least board maintainers will be more actively aware of needing to deal with in U-Boot, if it's really a problem.
Agree, also per discussion with Linux DT maintainers, they do care for DT backwards and forward compatibility. I expect the ABI changes to be rare. In case there is an ABI change then it will be great if Linux DT maintainers can ask contributors to CC corresponding U-boot platform maintainers too.
BTW, Rob is already working on a tool to detect ABI changes as he described here [1]. If U-boot platform maintainers have any ideas regarding what would constitute an ABI change then feel free to share those.
[1] https://lore.kernel.org/all/CAL_JsqLo4nXrJ93dDsfp3UYLs08V02aMnbCCnsDj0MBBomc...
So I would plan on grabbing only full kernel releases and in to -next as soon as possible. Our cadences don't match up exactly, but I think do fairly well enough.
I suppose that would give ample time to the U-boot platform/board maintainer to fix any ABI change regression found in the -next branch. That being said we aren't completely immune to changes to devicetree-rebasing subtree. If there is an DT ABI change that will take significant effort to fix in U-boot then we are open to accepting a revert given that it will be fixed before next uprev.
-Sumit
-- Tom