Messages in this thread | | | Date | Sat, 11 Jan 2014 00:48:48 +0800 | From | Chen Gang F T <> | Subject | Re: [PATCH v3] arm: remove !CPU_V6 and !GENERIC_ATOMIC64 build dependencies for XEN |
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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 <stefano.stabellini@eu.citrix.com> >>>>> 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
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