From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940915AbdEXREw (ORCPT ); Wed, 24 May 2017 13:04:52 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:24770 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752901AbdEXREa (ORCPT ); Wed, 24 May 2017 13:04:30 -0400 Subject: Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) To: Arnd Bergmann Cc: Geert Uytterhoeven , "David S. Miller" , Peter Zijlstra , Ingo Molnar , sparclinux , "linux-kernel@vger.kernel.org" , Linux-Arch , "devicetree@vger.kernel.org" , "linux-serial@vger.kernel.org" References: <8ec12d9b-30da-6088-e340-93cc92245ed4@oracle.com> From: Babu Moger Organization: Oracle Corporation Message-ID: <9d446ade-e3ef-f694-2b9b-f82e5ef463cb@oracle.com> Date: Wed, 24 May 2017 12:03:38 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/24/2017 10:09 AM, Arnd Bergmann wrote: > On Wed, May 24, 2017 at 4:45 PM, Babu Moger wrote: >> On 5/24/2017 5:18 AM, Arnd Bergmann wrote: >>> On Wed, May 24, 2017 at 11:59 AM, Geert Uytterhoeven >>> wrote: >>>> On Tue, May 23, 2017 at 11:45 PM, Babu Moger >>>> wrote: >>>> include/asm-generic/qrwlock.h is also generic, but depends on the >>>> architecture to select ARCH_USE_QUEUED_RWLOCKS, which only very few do >>>> (x86, and now sparc). >>>> >>>> I guess the time is ripe for adding (both) symbols to all architectures? >>> Good idea. I think we can do most of this by adding a few lines to >>> arch/Kconfig: >>> >>> config CPU_BIG_ENDIAN >>> bool >>> >>> config CPU_LITTLE_ENDIAN >>> def_bool !CPU_BIG_ENDIAN >> I noticed that even x86 does not define CPU_LITTLE_ENDIAN. Strange. > There is no architecture-independent code that tests for > CONFIG_CPU_LITTLE_ENDIAN, unlike CONFIG_CPU_BIG_ENDIAN, > so that's not very suprising. Ok. Thanks >> With this code all the architecture will default to >> CONFIG_CPU_LITTLE_ENDIAN. > What I meant is that we have to 'select CPU_BIG_ENDIAN' on all architectures > that actually are big-endian: Ok. Sure. > > These are all configurable: > $ git grep -l linux/byteorder/big_endian.h | xargs grep -l > linux/byteorder/little_endian.h > arch/arc/include/uapi/asm/byteorder.h > arch/arm/include/uapi/asm/byteorder.h > arch/arm64/include/uapi/asm/byteorder.h > arch/c6x/include/uapi/asm/byteorder.h > arch/m32r/include/uapi/asm/byteorder.h > arch/microblaze/include/uapi/asm/byteorder.h > arch/mips/include/uapi/asm/byteorder.h > arch/powerpc/include/uapi/asm/byteorder.h > arch/sh/include/uapi/asm/byteorder.h > arch/tile/include/uapi/asm/byteorder.h > > These are always big-endian: > $ git grep -l linux/byteorder/big_endian.h | xargs grep -L > linux/byteorder/little_endian.h > arch/avr32/include/uapi/asm/byteorder.h > arch/frv/include/uapi/asm/byteorder.h > arch/m68k/include/uapi/asm/byteorder.h > arch/openrisc/include/uapi/asm/byteorder.h > arch/parisc/include/uapi/asm/byteorder.h > arch/s390/include/uapi/asm/byteorder.h > arch/sparc/include/uapi/asm/byteorder.h > > And these are always little-endian: > arch/alpha/include/uapi/asm/byteorder.h > arch/blackfin/include/uapi/asm/byteorder.h > arch/cris/include/uapi/asm/byteorder.h > arch/hexagon/include/uapi/asm/byteorder.h > arch/ia64/include/uapi/asm/byteorder.h > arch/metag/include/uapi/asm/byteorder.h > arch/mn10300/include/uapi/asm/byteorder.h > arch/score/include/uapi/asm/byteorder.h > arch/unicore32/include/uapi/asm/byteorder.h > arch/x86/include/uapi/asm/byteorder.h > > So if we 'select CPU_BIG_ENDIAN' from avr32, frv, m68k, openrisc, parisc, > s390 and sparc, this covers all the fixed-endian architectures, and the > other ones are those that already have either CPU_BIG_ENDIAN > as a 'bool' option, or both as a 'choice'. Ok. Great details. I think I have all the details required for the first version. Will post it soon. Thanks >> I can make it as a separate patch. But I can only test SPARC and little bit >> of x86. Is that ok? > I think that's ok. > > Arnd