Re: ACPI vs DT at runtime

[Stefano Stabellini <stefano.stabellini-mvvWK6WmYclDPfheJLI6IQ@public.gmane.org>]

On Fri, 15 Nov 2013, Olof Johansson wrote:
> On Fri, Nov 15, 2013 at 12:58 PM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> > On Friday 15 November 2013, Olof Johansson wrote:
> >> So, I'm strongly urging that whatever the server guys try to do, it
> >> will in the end result in the ACPI data being translated into DT
> >> equivalents, such that the kernel only needs to handle data via DT.
> >
> > I don't think that a translation layer is the answer, I see the problem
> > more in things that cannot be translated automatically. The parts that
> > are similar enough to allow translation could also just be handled by
> > a thin abstraction layer in the kernel, which I think we will see
> > on embedded x86 with DT-in-ACPI-syntax.
> 
> I'm not so sure that converting everything yet again to another
> abstraction layer is a good solution. We've got one level of
> abstraction today -- DT. And we've got the un-abstracted layer of
> platform devices. Churning all drivers yet again seems like the wrong
> way to do this. For things that we can pre-populate instead of adding
> runtime abstraction, we should.

Simply using DT would help avoiding the awkward situation where a driver
of a device only works with one of the two description formats and not
the other.


> > I think we can still treat ACPI on ARM64 as a beginner's mistake and
> > provide hand-written DT blobs for the few systems that start shipping
> > with that.
> 
> I think we can do better -- we can ask those vendors to not ship ACPI
> at all, and ship DT themselves (together with us for review, etc).

They can ship with ACPI if they want to, what is important is that they
ship with device tree too.
Encouraging them to do that is definitely the right thing to do today,
regardless of the medium to long term ACPI strategy for the Linux
kernel.


> Especially since doing a broken ACPI implementation today _just for
> us_ will just distract them. If they need one for RT, fine. As I
> mentioned elsewhere, shipping a flashed DTB is no different from
> shipping ACPI from a future-proof point of view; we'll end up
> overriding either at some point once we figure out things better.

Well said.
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