From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750968AbdE3C4r (ORCPT ); Mon, 29 May 2017 22:56:47 -0400 Received: from ozlabs.org ([103.22.144.67]:39933 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750811AbdE3C4p (ORCPT ); Mon, 29 May 2017 22:56:45 -0400 From: Michael Ellerman To: Geert Uytterhoeven 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" 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: <87a85v7to2.fsf@concordia.ellerman.id.au> User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Tue, 30 May 2017 12:56:39 +1000 Message-ID: <877f0z6oig.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: > 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. cheers