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SubjectRe: [PATCH v3] arm: remove !CPU_V6 and !GENERIC_ATOMIC64 build dependencies for XEN
On Mon, Jan 20, 2014 at 03:32:48PM +0000, Stefano Stabellini wrote:
> On Thu, 16 Jan 2014, Will Deacon wrote:
> > For the xchg part, yes, that looks a lot better. I don't like the #undef
> > CONFIG_CPU_V6 though, can that be rewritten to use __LINUX_ARM_ARCH__?
>
> The problem is that the 1 and 2 byte parameter size cases in __cmpxchg
> are ifdef'ed CONFIG_CPU_V6 but drivers/xen/grant-table.c needs them.
>
> So we can either undef CONFIG_CPU_V6 in grant-table.c or call a
> different function.
>
> If I switch from ifdef CONFIG_CPU_V6 to if __LINUX_ARM_ARCH__ > 6 in
> __cmpxchg, we still have the problem that if __LINUX_ARM_ARCH__ == 6,
> grant-table.c doesn't compile.
>
> Maybe the approach taken by the other patch for cmpxchg is better, see
> below.

Yes, I prefer this approach. Minor comment below.

> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index c1f1a7e..ae54ae0 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1881,8 +1881,7 @@ config XEN_DOM0
> config XEN
> bool "Xen guest support on ARM (EXPERIMENTAL)"
> depends on ARM && AEABI && OF
> - depends on CPU_V7 && !CPU_V6
> - depends on !GENERIC_ATOMIC64
> + depends on CPU_V7
> select ARM_PSCI
> select SWIOTLB_XEN
> help
> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
> index df2fbba..cc8a4a2 100644
> --- a/arch/arm/include/asm/cmpxchg.h
> +++ b/arch/arm/include/asm/cmpxchg.h
> @@ -133,6 +133,44 @@ extern void __bad_cmpxchg(volatile void *ptr, int size);
> * cmpxchg only support 32-bits operands on ARMv6.
> */
>
> +static inline unsigned long __cmpxchg8(volatile void *ptr, unsigned long old,
> + unsigned long new)
> +{
> + unsigned long oldval, res;
> +
> + do {
> + asm volatile("@ __cmpxchg1\n"
> + " ldrexb %1, [%2]\n"
> + " mov %0, #0\n"
> + " teq %1, %3\n"
> + " strexbeq %0, %4, [%2]\n"
> + : "=&r" (res), "=&r" (oldval)
> + : "r" (ptr), "Ir" (old), "r" (new)
> + : "memory", "cc");
> + } while (res);
> +
> + return oldval;
> +}
> +
> +static inline unsigned long __cmpxchg16(volatile void *ptr, unsigned long old,
> + unsigned long new)
> +{
> + unsigned long oldval, res;
> +
> + do {
> + asm volatile("@ __cmpxchg1\n"

Can you fix this comment while you're here please?

Will


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