From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754080AbdFGXIr (ORCPT ); Wed, 7 Jun 2017 19:08:47 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:41462 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753775AbdFGXIo (ORCPT ); Wed, 7 Jun 2017 19:08:44 -0400 Subject: Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) To: Michael Ellerman , Geert Uytterhoeven Cc: "David S. Miller" , Peter Zijlstra , Ingo Molnar , Arnd Bergmann , sparclinux , "linux-kernel@vger.kernel.org" , Linux-Arch , "devicetree@vger.kernel.org" , "linux-serial@vger.kernel.org" References: <87a85v7to2.fsf@concordia.ellerman.id.au> <877f0z6oig.fsf@concordia.ellerman.id.au> From: Babu Moger Organization: Oracle Corporation Message-ID: <28d6c874-4653-b15d-39b7-57a032abc9c6@oracle.com> Date: Wed, 7 Jun 2017 18:07:20 -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: <877f0z6oig.fsf@concordia.ellerman.id.au> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/29/2017 9:56 PM, Michael Ellerman wrote: > Geert Uytterhoeven writes: > >> Hi Michael, >> >> On Mon, May 29, 2017 at 2:07 PM, Michael Ellerman wrote: >>> Geert Uytterhoeven writes: >>>> On Tue, May 23, 2017 at 11:45 PM, Babu Moger wrote: >>>>> Found this problem while enabling queued rwlock on SPARC. >>>>> The parameter CONFIG_CPU_BIG_ENDIAN is used to clear the >>>>> specific byte in qrwlock structure. Without this parameter, >>>>> we clear the wrong byte. Here is the code. >>>>> >>>>> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock) >>>>> { >>>>> return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN); >>>>> } >>>>> >>>>> Define CPU_BIG_ENDIAN for SPARC to fix it. >>>>> --- a/arch/sparc/Kconfig >>>>> +++ b/arch/sparc/Kconfig >>>>> @@ -92,6 +92,10 @@ config ARCH_DEFCONFIG >>>>> config ARCH_PROC_KCORE_TEXT >>>>> def_bool y >>>>> >>>>> +config CPU_BIG_ENDIAN >>>>> + bool >>>>> + default y if SPARC >>>> Nice catch! >>>> >>>> Traditionally, CPU_BIG_ENDIAN and CPU_LITTLE_ENDIAN were defined only on >>>> architectures that may support both. And it was checked in platform code >>>> and drivers only. >>>> Hence the symbol is lacking from most architectures. Heck, even >>>> architectures that support both may default to one endiannes, and declare >>>> only the symbol for the other endianness: >>> I guess there's a reason we can't use __BIG_ENDIAN__ / __LITTLE_ENDIAN__ ? >> I (C/asm) code we can, in Kconfig we cannot. >> >> So far we tried always doing that, but a few checks for the semi-existing >> Kconfig symbol crept in in generic code. Those could be replaced by the __*__ >> variants, but consistently having the Kconfig symbols would be useful anyway >> (e.g. to avoid building the broken-on-big-endian ISDN drivers). > Ah OK, the original mail was citing C code, but yeah I guess it would be > handy in Makefiles etc. Thanks for all the responses. I see couple of options here. 1. Fix the c code in include/asm-generic/qrwlock.h using ifdef __BIG_ENDIAN__ This will fix the issue for us. 2. Define CPU_BIG_ENDIAN for all the missing fixed endian architectures. Because the problem is only for fixed big endian archs. I prefer the option 1. What do you guys think ? > cheers