linux-kernel - Re: Making ARM multiplatform kernels DT-only?

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Date:	Fri, 04 May 2012 11:22:55 +0200
From:	Arnaud Patard (Rtp) <arnaud.patard@...-net.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arnd Bergmann <arnd@...db.de>, Kukjin Kim <kgene.kim@...sung.com>,
	linaro-dev@...ts.linaro.org, Jason Cooper <jason@...edaemon.net>,
	Nicolas Pitre <nico@...xnic.net>,
	Tony Lindgren <tony@...mide.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Deepak Saxena <dsaxena@...aro.org>,
	Olof Johansson <olof@...om.net>,
	David Brown <davidb@...eaurora.org>, shawn.guo@...aro.org,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Making ARM multiplatform kernels DT-only?

Russell King - ARM Linux <linux@....linux.org.uk> writes:

Hi,

> On Thu, May 03, 2012 at 01:50:35PM +0000, Arnd Bergmann wrote:
>> 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.
>
> On this point, I strongly object, especially as I'm one who uses the
> existing non-DT multiplatform support extensively.  It's really not
> a problem for what you're trying to achieve.
>

Please, don't do this. afaik, the idea was to reduce the numbers of
kernel to deal with. Unfortunately, this kind of restriction would
increase it. Consider orion platforms. This would mean having to deal
with 4 kernels (1 for DT, 1 for orion5x, 1 for kirkwood, 1 for mv78xx0).

Dropping HW support because one wants to encourage people to convert
their board file into DT seems weird. Doing this, imho, should even be
called a regression. The DT conversion won't happen in an eye blink so
non-DT kernels are still something we should take care of.

> I think what you're proposing is a totally artificial restriction.
> There's no problem with a kernel supporting DT and non-DT together.
> We've proven that many many times.  I prove it _every_ night that my
> build and boot system runs - the OMAP LDP boots a multiplatform kernel
> just fine without DT.

I think it's true for imx too. iirc, one can build a single image for
armv4/armv5 and one other for armv6/armv7 without having to use DT.

Regards,
Arnaud
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