[PATCH v3] arm: remove !CPU_V6 and !GENERIC_ATOMIC64 build dependencies for XEN

[Jaccon Bastiaansen]

2014/1/10 Chen Gang F T <chen.gang.flying.transformer at gmail.com>:
> 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 at eu.citrix.com>
>>>>>> CC: arnd at arndb.de
>>>>>> CC: linux at arm.linux.org.uk
>>>>>> CC: will.deacon at arm.com
>>>>>> CC: gang.chen at asianux.com
>>>>>> CC: catalin.marinas at arm.com
>>>>>> CC: jaccon.bastiaansen at gmail.com
>>>>>> CC: linux-arm-kernel at lists.infradead.org
>>>>>> CC: linux-kernel at 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

I agree with Will,

Regards,
  Jaccon