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In-Reply-To: <1236611904-9843-1-git-send-email-timur@freescale.com>
References: <1236611904-9843-1-git-send-email-timur@freescale.com>
Date: Mon, 9 Mar 2009 15:31:31 +0000
Message-ID: <87a5b0800903090831l6a74b8afhd640ce880be36114@mail.gmail.com>
Subject: Re: [PATCH v2] add function spin_event_timeout()
From: Will Newton <will.newton@gmail.com>
To: Timur Tabi <timur@freescale.com>
Cc: linux-kernel@vger.kernel.org, rdreier@cisco.com, jirislaby@gmail.com
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On Mon, Mar 9, 2009 at 3:18 PM, Timur Tabi <timur@freescale.com> wrote:
> The function spin_event_timeout() takes a condition and timeout value
> (in jiffies) as parameters. ?It spins until either the condition is true
> or the timeout expires. ?It returns non-zero if the condition is true,
> zero otherwise.
>
> Signed-off-by: Timur Tabi <timur@freescale.com>
> ---
>
> v2: changes based on feedback
>
> ?include/linux/delay.h | ? 22 ++++++++++++++++++++++
> ?1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/delay.h b/include/linux/delay.h
> index fd832c6..235ca25 100644
> --- a/include/linux/delay.h
> +++ b/include/linux/delay.h
> @@ -51,4 +51,26 @@ static inline void ssleep(unsigned int seconds)
> ? ? ? ?msleep(seconds * 1000);
> ?}
>
> +/**
> + * spin_event_timeout - spin until a condition gets true or a timeout elapses
> + * @condition: a C expression for the event to wait for
> + * @timeout: timeout, in jiffies
> + *
> + * The process spins until the @condition evaluates to true or the @timeout
> + * elapses.
> + *
> + * The function returns non-zero if the @condition evaluated to true, or
> + * zero if the @timeout elapsed. ?If both occurs (e.g. the loop was
> + * pre-empted and the @condition became true in the meantime, but when the
> + * loop resumed the @timeout had already elapsed), then non-zero will be
> + * returned.
> + */
> +#define spin_event_timeout(condition, timeout) ? ? ? ? ? ? ? ? \
> +({ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? \
> + ? ? ? unsigned long __timeout = jiffies + (timeout); ? ? ? ? ?\
> + ? ? ? while (!(condition) && time_before(jiffies, __timeout)) \
> + ? ? ? ? ? ? ? cpu_relax(); ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?\
> + ? ? ? (condition); ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?\
> +})
> +
> ?#endif /* defined(_LINUX_DELAY_H) */

Are you sure you want to evaluate condition a second time when
returning? Some memory mapped registers don't have a stable value so
e.g. the first test could succeed but the return value could still be
zero.

> --
> 1.6.1.3
>
> --
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