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Date: Wed, 6 Dec 2006 11:24:58 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: David Howells <dhowells@redhat.com>
cc: torvalds@osdl.org, akpm@osdl.org, linux-arm-kernel@lists.arm.linux.org.uk,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch
 doesn't support it [try #2]
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References: <20061206175622.31077.96046.stgit@warthog.cambridge.redhat.com>
 <Pine.LNX.4.64.0612061101110.27047@schroedinger.engr.sgi.com>
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Have a look at arch/i386/kernel/cpu/intel.c. You can probably replace my 
code that simulates cmpxchg for 386s

arch/i386/kernel/cpu/intel.c:

#ifndef CONFIG_X86_CMPXCHG
unsigned long cmpxchg_386_u8(volatile void *ptr, u8 old, u8 new)
{
        u8 prev;
        unsigned long flags;

        /* Poor man's cmpxchg for 386. Unsuitable for SMP */
        local_irq_save(flags);
        prev = *(u8 *)ptr;
        if (prev == old)
                *(u8 *)ptr = new;
        local_irq_restore(flags);
        return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u8);

unsigned long cmpxchg_386_u16(volatile void *ptr, u16 old, u16 new)
{
        u16 prev;
        unsigned long flags;

        /* Poor man's cmpxchg for 386. Unsuitable for SMP */
        local_irq_save(flags);
        prev = *(u16 *)ptr;
        if (prev == old)
                *(u16 *)ptr = new;
        local_irq_restore(flags);
        return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u16);

unsigned long cmpxchg_386_u32(volatile void *ptr, u32 old, u32 new)
{
        u32 prev;
        unsigned long flags;

        /* Poor man's cmpxchg for 386. Unsuitable for SMP */
        local_irq_save(flags);
        prev = *(u32 *)ptr;
        if (prev == old)
                *(u32 *)ptr = new;
        local_irq_restore(flags);
        return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u32);
#endif