From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [PATCHv2 3/6] xen: generic xadd() for ticket locks
Date: Tue, 14 Apr 2015 14:17:08 +0100
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References: <1428675597-28465-1-git-send-email-david.vrabel@citrix.com>
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To: David Vrabel <david.vrabel@citrix.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>, Jan Beulich <jbeulich@suse.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
List-Id: xen-devel@lists.xenproject.org

On Fri, 2015-04-10 at 15:19 +0100, David Vrabel wrote:
> This is only temporary until arm/arm64 provides an xadd()
> implementation.

I'll assume that you aren't planning on doing this and add it to my own
TODO list. Although, I'm more than willing to be preempted by another
ARM dev...

> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  xen/common/spinlock.c |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
> index 5fd8b1c..0c4289c 100644
> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -10,6 +10,27 @@
>  #include <asm/processor.h>
>  #include <asm/atomic.h>
>  
> +#ifndef xadd
> +
> +static u32 generic_xaddl(volatile u32 *ptr, u32 v)
> +{
> +    u32 old, new, prev;
> +
> +    old = read_atomic(ptr);
> +    for(;;) {
> +        new = old + v;
> +        prev = cmpxchg(ptr, old, new);
> +        if (prev == old)
> +            break;
> +        old = prev;
> +    }
> +    return old;
> +}
> +
> +#define xadd(ptr, v) generic_xaddl((ptr), (v))
> +
> +#endif
> +
>  #ifndef NDEBUG
>  
>  static atomic_t spin_debug __read_mostly = ATOMIC_INIT(0);