[PATCH v7] introduce macro spin_event_timeout()

[Grant Likely]

On Tue, May 5, 2009 at 3:53 PM, Timur Tabi <timur at freescale.com> wrote:
> The macro spin_event_timeout() takes a condition and timeout value
> (in microseconds) as parameters.  It spins until either the condition is true
> or the timeout expires.  It returns the result of the condition when the loop
> was terminated.
>
> This primary purpose of this macro is to poll on a hardware register until a
> status bit changes.  The timeout ensures that the loop still terminates if the
> bit doesn't change as expected.  This macro makes it easier for driver
> developers to perform this kind of operation properly.
>
> Signed-off-by: Timur Tabi <timur at freescale.com>

This version looks good to me.  Who's the first user? (I'd like to see
that something is ready to use this before merging it)

Acked-by: Grant Likely <grant.likely at secretlab.ca>

> ---
>
> v7: add if-statement to use cpu_relax() if the delay is 0.  gcc will optimize
> out the if-statement if 'delay' is a constant.
>
> I'm making this a PowerPC-specific patch because I want to use
> tb_ticks_per_usec, which does not exist on all other platforms.  I don't want
> to use jiffies because jiffies works only when interrupts are enabled, and
> the resolution may not be fine enough.
>
>  arch/powerpc/include/asm/delay.h |   32 ++++++++++++++++++++++++++++++++
>  1 files changed, 32 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h
> index f9200a6..2bde26f 100644
> --- a/arch/powerpc/include/asm/delay.h
> +++ b/arch/powerpc/include/asm/delay.h
> @@ -2,6 +2,8 @@
>  #define _ASM_POWERPC_DELAY_H
>  #ifdef __KERNEL__
>
> +#include <asm/time.h>
> +
>  /*
>  * Copyright 1996, Paul Mackerras.
>  *
> @@ -30,5 +32,35 @@ extern void udelay(unsigned long usecs);
>  #define mdelay(n)      udelay((n) * 1000)
>  #endif
>
> +/**
> + * spin_event_timeout - spin until a condition gets true or a timeout elapses
> + * @condition: a C expression to evalate
> + * @timeout: timeout, in microseconds
> + * @delay: the number of microseconds to delay between eache evaluation of
> + *         @condition
> + * @rc: the last value of the condition
> + *
> + * The process spins until the condition evaluates to true (non-zero) or the
> + * timeout elapses.  Upon exit, @rc contains the value of the condition. This
> + * allows you to test the condition without incurring any side effects.
> + *
> + * This primary purpose of this macro is to poll on a hardware register
> + * until a status bit changes.  The timeout ensures that the loop still
> + * terminates even if the bit never changes.  The delay is for devices that
> + * need a delay in between successive reads.
> + *
> + * gcc will optimize out the if-statement if @delay is a constant.
> + */
> +#define spin_event_timeout(condition, timeout, delay, rc)                   \
> +{                                                                           \
> +       unsigned long __loops = tb_ticks_per_usec * timeout;                \
> +       unsigned long __start = get_tbl();                                  \
> +       while (!(rc = (condition)) && (tb_ticks_since(__start) <= __loops)) \
> +               if (delay)                                                  \
> +                       udelay(delay);                                      \
> +               else                                                        \
> +                       cpu_relax();                                        \
> +}
> +
>  #endif /* __KERNEL__ */
>  #endif /* _ASM_POWERPC_DELAY_H */
> --
> 1.6.0.6
>
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>



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.