From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751099AbdE2MPl (ORCPT ); Mon, 29 May 2017 08:15:41 -0400 Received: from mail-it0-f65.google.com ([209.85.214.65]:35659 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750925AbdE2MPh (ORCPT ); Mon, 29 May 2017 08:15:37 -0400 MIME-Version: 1.0 In-Reply-To: <87a85v7to2.fsf@concordia.ellerman.id.au> References: <87a85v7to2.fsf@concordia.ellerman.id.au> From: Geert Uytterhoeven Date: Mon, 29 May 2017 14:15:35 +0200 X-Google-Sender-Auth: 5DSKACztLeFbiNQOyGKk_PvH1FU Message-ID: 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 Cc: Babu Moger , "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" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds