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Message-ID: <20120503140428.GB897@n2100.arm.linux.org.uk>
Date: Thu, 3 May 2012 15:04:28 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linaro-dev@...ts.linaro.org,
Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
Deepak Saxena <dsaxena@...aro.org>,
Tony Lindgren <tony@...mide.com>,
Linus Walleij <linus.walleij@...aro.org>, shawn.guo@...aro.org,
Sascha Hauer <s.hauer@...gutronix.de>,
Magnus Damm <magnus.damm@...il.com>,
Kukjin Kim <kgene.kim@...sung.com>,
Olof Johansson <olof@...om.net>,
David Brown <davidb@...eaurora.org>,
Nicolas Pitre <nico@...xnic.net>,
Haojian Zhuang <haojian.zhuang@...il.com>,
Jason Cooper <jason@...edaemon.net>,
Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: Making ARM multiplatform kernels DT-only?
On Thu, May 03, 2012 at 01:50:35PM +0000, Arnd Bergmann wrote:
> Hi everyone,
>
> I've been discussing multiplatform kernels with a few people recently,
> and we will have a lot of discussion sessions about this at Linaro
> Connect in Hong Kong.
>
> One question that came up repeatedly is whether we should support all
> possible board files for each platform in a multiplatform kernel,
> or just the ones that are already using DT probing. I would like
> to get a quick poll of opinions on that and I've tried to put those
> people on Cc that would be most impacted by this, i.e. the maintainers
> for platforms that have both DT and non-DT board files at the moment.
>
> My feeling is that we should just mandate DT booting for multiplatform
> kernels, because it significantly reduces the combinatorial space
> at compile time, avoids a lot of legacy board files that we cannot
> test anyway, reduces the total kernel size and gives an incentive
> for people to move forward to DT with their existing boards.
>
> The counterargument is that we won't be able to support all the
> boards we currently do when the user switches on multiplatform,
> but I think that is acceptable.
> Note that I would still want to allow users to build platforms
> separately in order to enable the ATAG style board files, even
> for platforms that are not multiplatform capable.
I'm basing my comments off mach-zynq.
How about we take the following steps towards it?
1. create arch/arm/include/mach/ which contains standardized headers
for DT based implementations. This must include all headers included
by asm/ or linux/ includes. This will also be the only mach/ header
directory included for code outside of arch/arm/mach-*. This also
acts as the 'default' set of mach/* includes for stuff like timex.h
and the empty hardware.h
2. DT based mach-* directories do not have an include directory; their
include files must be located in the main include/ heirarchy if shared
with other parts of the kernel, otherwise they must be in the mach-*
directory.
3. Allow build multiple mach-* directories (which we already do... see
the samsung stuff.)
We still have irqs.h being SoC dependent, and we still haven't taken
debug-macros.S far enough along to get rid of that. Then there's also
the problem of uncompress.h. The last piece of the puzzle is the common
clock stuff.
So, I think we're still a way off it yet - maybe six months or so.
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