[PATCH v3 5/8] doc: devicetree: Updates for devicetree-rebasing subtree

[Tom Rini]

On Thu, Jan 04, 2024 at 06:52:32PM +0530, Sumit Garg wrote:
> Hi Michal,
> 
> On Thu, 4 Jan 2024 at 15:39, Michal Simek <michal.simek at amd.com> wrote:
> >
> >
> >
> > On 1/3/24 17:32, Tom Rini wrote:
> > > On Wed, Jan 03, 2024 at 09:19:40AM -0700, Rob Herring wrote:
> > >> On Thu, Dec 28, 2023 at 4:59 AM Sumit Garg <sumit.garg at linaro.org> wrote:
> > > [snip]
> > >>> +In order to maintain devicetree files sync, U-Boot maintains a Git subtree for
> > >>> +devicetee-rebasing repo as `devicetee-rebasing/` sub-directory. It is regularly
> > >>> +kept updated with every new kernel major release via subtree pull as follows::
> > >>
> > >> I would suggest dropping "-rebasing" in the u-boot tree. (I wish we
> > >> had in the original repo). I don't think it's relevant.
> > >>
> > >> We're not likely to regenerate the tree, but any clue what 'git
> > >> subtree pull' would do in this case? It could happen if we switched to
> > >> git-filter-repo.
> > >>
> > >>> +
> > >>> +    git subtree pull --prefix devicetree-rebasing \
> > >>> +        git://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git \
> > >>> +        <release-tag> --squash
> > >>
> > >> I'd put this in a script to run. Documentation tends to be not quite
> > >> correct. A script could also be smarter and figure out <release-tag>.
> > >
> > > Since you had mentioned elsewhere moving the kernel scripts/dtc/ to
> > > something using subtree, I do hope to learn some lessons from what you
> > > do there. The first thing is that given the size/nature of the commits,
> > > I had figured I'd be the one doing this as a subtree pull+squash then
> > > push, rather than posting to the ML since it'll be huge and
> > > un-reviewable, but with a note sent off to the ML that people should be
> > > aware the next sync has been done and retest as needed. But Sumit, were
> > > you planning to do some of this instead?  The second thing is that if we
> > > move the subtree part in to dts/ instead (where we will still have the
> > > Makefile/Kconfig we have today and then our Makefiles within the
> > > directories, this might get more complex and so really require a script
> > > to keep it from getting error prone?
> >
> > I played with this series and didn't really have time to dig into subtree
> > mechanics but one thing I see is that when squash and merge happens you can't do
> > simple rebase anymore which is time to time very useful.
> > I see some different rebase strategies and --rebase-merges option but if this is
> > adopted it should be properly described how to rebase u-boot tree which contains
> > some subtrees.
> 
> Did you observe any specific difference with respect to subtree merge
> commits (Tom will likely do those in the beginning of next release
> cycle) when compared with normal merge commits when Tom pulls in code
> from different custodians like one example below? The same rebasing
> rules should apply to both types of merge commits.
> 
> commit dffa6d0210f57793f1e4e1e209d91ca5642e4d05 (origin/next)
> Merge: 2b28c3b871c e266d273114
> Author: Tom Rini <trini at konsulko.com>
> Date:   Mon Jan 1 12:38:15 2024 -0500
> 
>     Merge tag 'dm-next-1124' of
> https://source.denx.de/u-boot/custodians/u-boot-dm into next
> 
>     support propagating supernode properties with bootph schema
>     align bloblist with v0.9 of Firmware Handoff spec

There's two cases. The first and uncommon case is that if you want to do
something like:
- Branch next
- Add this subtree, do a few subtree updates on it (like my experiment
  of starting with v6.1-dts and merging up to v6.6-dts)
- Wait a while, have changes happen in next
- Rebase on to current next

It gets painful and odd, but I don't know that this will ever really
happen.

The second, common case is:
- Assume "next" already has this subtree + some merge commits in it.
- Make a new local branch.
- Make change in your new local branch.
- This hypothetical "next" branch moves forward with changes
- Rebase your local branch on to this "next" branch

In this case things work as expected. Even if  "next" in that case gets
a new subtree merge that you need to rebase in.

A third case that I'm not sure if really will happen or is a case where
the custodian should rework their tree instead (to drop the subtree
merge) is:
- Assume "next" already has this subtree + some merge commits in it.
- Make a new local branch.
- Make a subtree merge+squash in your local branch.
- This hypothetical "next" branch moves forward with changes
- Rebase your local branch on to this "next" branch.

This will then make you try and resolve some conflicts from that subtree
merge.  But is this a valid use case? Yes, I can see wanting to get a
start on testing a dts merge before it happens, but is this a tree which
needs to be rebased, or just re-created as needed, if the parent branch
moves forward?

Can you explain a bit more your case Michal since it sounded to me like
you had a problem that happened rather than a worry about what might
happen?

-- 
Tom
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