linux-kernel - Re: [PATCH v2] arch: Kconfig: Let all little endian architectures define CPU_LITTLE

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Date:	Wed, 13 Aug 2014 13:32:14 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Sam Ravnborg <sam@...nborg.org>
CC:	Arnd Bergmann <arnd@...db.de>, akpm@...ux-foundation.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jean Delvare <jdelvare@...e.de>, linux@....linux.org.uk,
	catalin.marinas@....com, will.deacon@....com, msalter@...hat.com,
	a-jacquiot@...com, tony.luck@...el.com, fenghua.yu@...el.com,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-c6x-dev@...ux-c6x.org, linux-ia64@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v2] arch: Kconfig: Let all little endian architectures
 define CPU_LITTLE_ENDIAN explicitly



On 8/13/14 13:08, Sam Ravnborg wrote:
> On Wed, Aug 13, 2014 at 06:48:35AM +0800, Chen Gang wrote:
>> x86 and ia64 are always little endian. And another architectures may be
>> little endian: mips, sh, powerpc, and m32r (may mark CPU_LITTLE_ENDIAN
>> explicitly); also arm(64) and c6x (which may be !CPU_BIG_ENDIAN).
>>
>> Some drivers (e.g. some of "drivers/isdn/hisax") may only support little
>> endian (CPU_LITTLE_ENDIAN), and some drivers may only support big endian
>> (!CPU_LITTLE_ENDIAN).
>>
>> So export all little endian architectures within kernel wide, so can let
>> Kconfig easier for the modules which only support little endian or only
>> for big endian (assume !CPU_LITTLE_ENDIAN is same as CPU_BIG_ENDIAN).
> We need to cover three cases here:
> - An arch supports only little endian
> - An arch supports only big endian
> - An arch may be both little and big endian
> 

Yeah, we need.

> The solution you suggest assumes that an arch is either little or big endian.
> But we cannot ignore the hybriads that can do both.
> 

For the architectures which can do both, for me, they are: sh, powerpc,
m32r, and mips (may mark CPU_LITTLE_ENDIAN), also are: arm/arm64, and
c6x (may mark !CPU_BIG_ENDIAN).

For the architectures which only support little endian: x86, and ia64.

The left, I assumes they are big endian (no any 'ENDIAN' can be found
in their Kconfig files). In my memory, except related with Intel, all
are (or support) big endian.


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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