From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751074AbdE2MHt (ORCPT ); Mon, 29 May 2017 08:07:49 -0400 Received: from ozlabs.org ([103.22.144.67]:55993 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750925AbdE2MHr (ORCPT ); Mon, 29 May 2017 08:07:47 -0400 From: Michael Ellerman To: Geert Uytterhoeven , Babu Moger 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" Subject: Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) In-Reply-To: References: User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Mon, 29 May 2017 22:07:41 +1000 Message-ID: <87a85v7to2.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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__ ? cheers