linux-kernel - Re: [patch 04/36] Hexagon: Add atomic ops support

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Message-ID: <1892721.uUY0g5DXJQ@wuerfel>
Date:	Wed, 17 Aug 2011 21:20:36 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Kuo <rkuo@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, linux-hexagon@...r.kernel.org
Subject: Re: [patch 04/36] Hexagon: Add atomic ops support

On Wednesday 17 August 2011 11:35:01 Richard Kuo wrote:
> +/**
> + * atomic_add_unless - add unless the number is a given value
> + * @v: pointer to value
> + * @a: amount to add
> + * @u: unless value is equal to u
> + *
> + * This is actually in the asm-generic version; should revisit this
> + * entire file...
> + */
> +static inline int __atomic_add_unless(atomic_t *v, int a, int u)
> +{
> +       int c, old;
> +
> +       c = atomic_read(v);
> +       for (;;) {
> +               if (unlikely(c == u))
> +                       break;
> +               old = atomic_cmpxchg((v), c, c + a);
> +               if (likely(old == c))
> +                       break;
> +               c = old;
> +       }
> +       return c != u;
> +}

It's probably worth doing this in a single inline assembly instead
of two nested loops (the second one being inside of atomic_cmpxchg.

	Arnd
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