Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756087AbaAJQsw (ORCPT ); Fri, 10 Jan 2014 11:48:52 -0500 Received: from mail-pd0-f171.google.com ([209.85.192.171]:32924 "EHLO mail-pd0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752175AbaAJQsv (ORCPT ); Fri, 10 Jan 2014 11:48:51 -0500 Message-ID: <52D02470.6050303@gmail.com> Date: Sat, 11 Jan 2014 00:48:48 +0800 From: Chen Gang F T User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Will Deacon CC: Stefano Stabellini , Arnd Bergmann , "linux-arm-kernel@lists.infradead.org" , "linux@arm.linux.org.uk" , Catalin Marinas , "gang.chen@asianux.com" , "linux-kernel@vger.kernel.org" , "jaccon.bastiaansen@gmail.com" Subject: Re: [PATCH v3] arm: remove !CPU_V6 and !GENERIC_ATOMIC64 build dependencies for XEN References: <1389204023-26912-1-git-send-email-stefano.stabellini@eu.citrix.com> <20140109103004.GB11089@mudshark.cambridge.arm.com> <201401091204.17932.arnd@arndb.de> <20140109184251.GL17838@mudshark.cambridge.arm.com> In-Reply-To: <20140109184251.GL17838@mudshark.cambridge.arm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/10/2014 02:42 AM, Will Deacon wrote: > On Thu, Jan 09, 2014 at 12:47:24PM +0000, Stefano Stabellini wrote: >> On Thu, 9 Jan 2014, Arnd Bergmann wrote: >>> On Thursday 09 January 2014, Will Deacon wrote: >>>> On Wed, Jan 08, 2014 at 06:00:23PM +0000, Stefano Stabellini wrote: >>>>> Remove !GENERIC_ATOMIC64 build dependency: >>>>> - rename atomic64_xchg to armv7_atomic64_xchg and define it even ifdef >>>>> GENERIC_ATOMIC64; >>>>> - call armv7_atomic64_xchg directly from xen/events.h. >>>>> >>>>> Remove !CPU_V6 build dependency: >>>>> - introduce __cmpxchg8 and __cmpxchg16, compiled even ifdef >>>>> CONFIG_CPU_V6; >>>>> - implement sync_cmpxchg using __cmpxchg8 and __cmpxchg16. >>>>> >>>>> Signed-off-by: Stefano Stabellini >>>>> CC: arnd@arndb.de >>>>> CC: linux@arm.linux.org.uk >>>>> CC: will.deacon@arm.com >>>>> CC: gang.chen@asianux.com >>>>> CC: catalin.marinas@arm.com >>>>> CC: jaccon.bastiaansen@gmail.com >>>>> CC: linux-arm-kernel@lists.infradead.org >>>>> CC: linux-kernel@vger.kernel.org >>>>> >>>> >>>> I'm confused here. It looks like you want to call armv7 code in a v6 kernel. >>>> What am I missing? >>> >>> This is about being able to build a kernel that runs on ARMv6 and ARMv7 >>> and also includes Xen. Because of obvious hardware limitations, Xen >>> will only run on v7, but currently you cannot even build it once you >>> enable (pre-v6K) ARMv6 support, since the combined v6+v7 kernel can't >>> do atomic accesses in a generic way on non-32bit variables. >> >> Yep, that's right. > > Ok, thanks for the explanation. Looking at the patch, I wonder whether it's > not cleaner just to implement xchg code separately for Xen? The Linux code > isn't always sufficient (due to the GENERIC_ATOMIC64 stuff) and most of the > churn coming out of this patch is an attempt to provide some small code > reuse at the cost of code readability. > > What do others think? > What Will said sounds reasonable to me. Thanks. -- Chen Gang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/