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Date: Tue, 10 Jul 2012 16:33:58 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 00/36] AArch64 Linux kernel port
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> In the AArch32 kernel port many implementation decisions newer
> architectures were made in a way that preserves backwards compatibility
> to over 15 years ago (and for *good* reasons, ARMv4 hardware is still in
> use). But keeping the same decisions in AArch64 is wrong.

Same argument as x86-32 v x86-64. Same issues about compatibility.

> AArch64 is also in its early days with a lot of developments to come
> (and still waiting for hardware). Until we really know the final shape,
> the AArch64 code base must allowed to evolve independently from the
> AArch32 one.

That is one area where while the merge was needed and a lot of work the
original split may well have been sensible for x86-64 as well.

> The initial target is servers (see the companies that have announced
> plans around ARMv8) but I agree, we may see it in other devices in the
> future. But as the maintainer I have no plans to support a 32-bit SoC on
> an AArch64/ARMv8 system (which may or may not support AArch32 at kernel
> level). If an AArch64 SoC would share some devices with an AArch32 SoC,
> such code will go to drivers/.

What plans to other maintainers and board vendors have ? Any design choice
has to cope with these happening if a third party goes and does it.

Alan