linux-kernel - Re: [GIT PULL] omap changes for v2.6.39 merge window

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Date:	Fri, 1 Apr 2011 23:32:23 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Kevin Hilman <khilman@...com>, david@...g.hm,
	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	Nicolas Pitre <nico@...xnic.net>,
	Tony Lindgren <tony@...mide.com>,
	Catalin Marinas <catalin.marinas@....com>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	linux-omap@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Brown <davidb@...eaurora.org>,
	Detlef Vollmann <dv@...lmann.ch>
Subject: Re: [GIT PULL] omap changes for v2.6.39 merge window

On Friday 01 April 2011 23:10:04 Kevin Hilman wrote:
> Arnd Bergmann <arnd@...db.de> writes:
> 
> > On Friday 01 April 2011, Detlef Vollmann wrote:
> >> On 04/01/11 15:54, Arnd Bergmann wrote:
> >
> >> > 9. All interesting work is going into a handful of platforms, all of which
> >> >     are ARMv7 based.
> >> Define interesting.
> >
> > The ones that are causing the churn that we're talking about.
> > Platforms that have been working forever and only need to get
> > the occasional bug fix are boring, i.e. not the problem.
> 
> I'm not sure I follow the ARMv7-only thinking either.  
> 
> Picking ARMv7 only would be a good way to avoid part of the problem, but
> IMO, it doesn't really address the root causes.  Part of the ugliness of
> the platform-specific hackery (and the "churn" to clean some of it up)
> is precisely due to support for multiple ARM architecture versions, and
> the various SoCs in a family that use them.  For example, linux-omap
> supports OMAP1 (ARMv5), OMAP2 (ARMv6), OMAP3 (ARMv7) and OMAP4 (ARMv7
> SMP), and OMAP2/3/4 in a single binary.
> 
> Also, since we've only very recently got to the point of being able to
> support ARMv6 + ARMv7 UP & SMP in the same kernel, making a decision now
> that only ARMv7 is important seems like a step backwards.  If the
> ultimate goal is getting to a point where we have infrastrucure that can
> be cross-SoC, surely this same infrastrucure should support multiple ARM
> architecture revisions.

Yes, forget about the ARMv7 part of my proposal, that was not a main point.

If we decide to have a new clean platform variant the way I suggested,
it would be nice to support all machines in a single kernel binary,
and at least v6+v7 is a solved problem.

Supporting a second kernel binary up to v5 with the same source is also
simple, as would be big-endian/little-endian variants, or thumb2/arm variants.
We might not want to do all combinations from the start though, and I would
choose ARMv6/v7-thumb2-le simply because that's what Linaro is focusing
on. The idea is to start with a clearly defined set, but write the code
in a way that makes it possible to extend in other directions.

	Arnd
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