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 <[email protected]> >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> CC: [email protected] >>>>> >>>> >>>> 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
