Re: [PATCH v2 6/7] arm: dts: apple: Add preliminary device trees

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Rob Herring <robh@kernel.org>
> Date: Mon, 11 Oct 2021 14:48:46 -0500

Hi Rob,

Trimming the CC list a bit and adding marcan.

> On Mon, Oct 11, 2021 at 2:00 PM Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >
> > > From: Rob Herring <robh@kernel.org>
> > > Date: Mon, 11 Oct 2021 13:36:29 -0500
> >
> > Hi Rob,
> >
> > > On Sun, Oct 3, 2021 at 1:35 PM Mark Kettenis <kettenis@openbsd.org> wrote:
> > > >
> > > > Add preliminary device trees for the Apple M1 mini (2020) and
> > > > Apple M1 Macbook Pro 13" (2020).  Device tree bindings for
> > > > the Apple M1 SoC are still being formalized and these device
> > > > trees will be synchronized with the Linux kernel as needed.
> > >
> > > So not synchronized currently? If it is sync'ed, you should specify
> > > which version you got.
> >
> > Not synched at the moment.  It is based on what was in 5.13 or 5.14,
> > but with lots of stuff added so specifying a version would be
> > misleading.  It should be mostly aligned with the bindings that are
> > making their way into 5.15 or 5.16 though.
> 
> This and what's added or preliminary would be good to have in the commit msg.

Sure.  I added that information to the commit message for v4.

> > Hopefully now that the power domains are getting addressed we'll have
> > something that can be synchronized soon.  I was explicitly encouraged
> > to start upstreaming the U-Boot code even though not all the DT
> > bindings had been sorted out.
> 
> In general, sounds like a recipe for getting out of sync and bindings
> never getting documented properly without any checks in place. The
> good news is checking that is at least possible now.
> 
> > > > These device trees are provided as a reference only as U-Boot
> > > > uses the device tree passed by the m1n1 bootloader.
> > >
> > > If reference only, why do they need to be checked in here? We're
> > > trying to get to fewer copies both of dtbs at runtime and dts files in
> > > source trees.
> >
> > The U-Boot maintainers insist there is a DT for each supported system
> > in the U-Boot tree.
> 
> Ok, fair enough.
> 
> > > I mainly bring it up here because this is a platform with multiple OS
> > > targets, following the model that DT comes from the firmware, and
> > > should be free of schema validation warnings. In other words, it's a
> > > good candidate to define best practices.
> >
> > You're preaching to the choir ;).
> 
> Good.
> 
> > Must admit that it is somewhat convenient for me to have a somewhat
> > complete DT for these devices at the moment.  But in the long run I
> > think it will just confuse people.  That said, I plan to be aggressive
> > in keeping the U-Boot tree synchronized with Linux.
> 
> What I'd like to see here is some sort of automatic synchronization.
> The idea I have here is just a list of boards to sync from the kernel
> tree to wherever. The requirement to get on the list would be passing
> schema validation and would be a declaration of stability (there's
> been numerous discussions over the years of how to declare a DT stable
> or unstable). It would perhaps also include passing validation on an
> older schema. I'm not sure how well that would catch compatibility
> issues, but that's the only idea I've come up with besides just
> testing of mixed versions. I'm happy to do the tooling to support that
> if we have a board/device to put in the list and u-boot folks agree to
> use it. I suppose even if just m1n1 used it to start with, I'd be
> willing to do the tooling.

Sounds interesting.

One of the things we would want to do a ship device trees for new
models with m1n1 as soon as we get our hands on the hardware such that
the they can be used with existing distro kernels as soon as possible.
Under the assumption that the new hardware is compatible with the old
of course.  That means those new device trees should pass validation.

But as soon as the device tree for a model is available in the Linux
tree, we probably want to be rather strict in synching it to m1n1.

Thanks,

Mark