[PATCH 1/2 v8] powerpc: introduce macro spin_event_timeout()

[Jon Smirl]

On Tue, May 19, 2009 at 3:26 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.


I just tried using this. The !rc has the effect of making the error
return be zero instead the normal not zero.

	/* Wait for command send status zero = ready */
	spin_event_timeout(!(in_be16(&psc_dma->psc_regs->sr_csr.status) &
				MPC52xx_PSC_SR_CMDSEND), 100, 0, rc);
	if (rc == 0) {
		pr_err("timeout on ac97 bus (rdy)\n");
		return -ENODEV;
	}

I want the register to be zero, would this be more obvious?

	/* Wait for command send status zero = ready */
	spin_event_timeout((in_be16(&psc_dma->psc_regs->sr_csr.status) &
				MPC52xx_PSC_SR_CMDSEND), 100, 0, rc);
	if (rc != 0) {
		pr_err("timeout on ac97 bus (rdy)\n");
		return -ENODEV;
	}


>
> Signed-off-by: Timur Tabi <timur at freescale.com>
> ---
>
> v8: added a copyright notice
>
>  arch/powerpc/include/asm/delay.h |   33 +++++++++++++++++++++++++++++++++
>  1 files changed, 33 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h
> index f9200a6..af4a270 100644
> --- a/arch/powerpc/include/asm/delay.h
> +++ b/arch/powerpc/include/asm/delay.h
> @@ -2,8 +2,11 @@
>  #define _ASM_POWERPC_DELAY_H
>  #ifdef __KERNEL__
>
> +#include <asm/time.h>
> +
>  /*
>  * Copyright 1996, Paul Mackerras.
> + * Copyright (C) 2009 Freescale Semiconductor, Inc. All rights reserved.
>  *
>  * This program is free software; you can redistribute it and/or
>  * modify it under the terms of the GNU General Public License
> @@ -30,5 +33,35 @@ 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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>



-- 
Jon Smirl
jonsmirl at gmail.com