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SubjectRe: [PATCH] sparc: Provide cmpxchg64 for 32-bit builds
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From: Guenter Roeck <linux@roeck-us.net>
Date: Wed, 27 Sep 2017 21:55:50 -0700

> On 09/27/2017 09:38 PM, David Miller wrote:
>> From: Guenter Roeck <linux@roeck-us.net>
>> Date: Sun, 24 Sep 2017 10:29:31 -0700
>>
>>> Fix the following build error, seen when building
>>> sparc32:allmodconfig.
>>>
>>> drivers/net/ethernet/intel/i40e/i40e_ethtool.c:
>>> In function 'i40e_set_priv_flags':
>>> drivers/net/ethernet/intel/i40e/i40e_ethtool.c:4150:2: error:
>>> implicit declaration of function 'cmpxchg64'
>>>
>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> That fixes the build:
>>
>>> @@ -72,5 +72,6 @@ __cmpxchg(volatile void *ptr, unsigned long old,
>>> unsigned long new_, int size)
>>> ((__typeof__(*(ptr)))__cmpxchg_local_generic((ptr), (unsigned long)(o),\
>>> (unsigned long)(n), sizeof(*(ptr))))
>>> #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr),
>>> #(o), (n))
>>> +#define cmpxchg64(ptr, o, n) cmpxchg64_local((ptr), (o), (n))
>>> #endif /* __ARCH_SPARC_CMPXCHG__ */
>> but it's wrong. cmpxchg64_local() is only atomic on the current cpu
>> so using it for plain cmpxchg64() is not going to work.
>>
>
> Yeah, I was concerned about that. My bad.
>
> Unfortunately I don't know enough about sparc to provide a better
> solution.
> Consider this a problem report, then.

I'll see what I can do. Something like this:

diff --git a/arch/sparc/include/asm/cmpxchg_32.h b/arch/sparc/include/asm/cmpxchg_32.h
index 83ffb83..7f95d3c 100644
--- a/arch/sparc/include/asm/cmpxchg_32.h
+++ b/arch/sparc/include/asm/cmpxchg_32.h
@@ -62,6 +62,8 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size)
(unsigned long)_n_, sizeof(*(ptr))); \
})

+extern u64 cmpxchg64(u64 *ptr, u64 old, u64 new);
+
#include <asm-generic/cmpxchg-local.h>

/*
diff --git a/arch/sparc/lib/atomic32.c b/arch/sparc/lib/atomic32.c
index 2c37332..41601eb 100644
--- a/arch/sparc/lib/atomic32.c
+++ b/arch/sparc/lib/atomic32.c
@@ -172,6 +172,20 @@ unsigned long __cmpxchg_u32(volatile u32 *ptr, u32 old, u32 new)
}
EXPORT_SYMBOL(__cmpxchg_u32);

+u64 cmpxchg64(u64 *ptr, u64 old, u64 new)
+{
+ unsigned long flags;
+ u64 prev;
+
+ spin_lock_irqsave(ATOMIC_HASH(ptr), flags);
+ if ((prev = *ptr) == old)
+ *ptr = new;
+ spin_unlock_irqrestore(ATOMIC_HASH(ptr), flags);
+
+ return prev;
+}
+EXPORT_SYMBOL(cmpxchg64);
+
unsigned long __xchg_u32(volatile u32 *ptr, u32 new)
{
unsigned long flags;
\
 
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