From 9317726de42a157c377f7fe9110a63260800582f Mon Sep 17 00:00:00 2001 From: Timur Tabi Date: Tue, 26 May 2009 05:21:41 +0000 Subject: powerpc: Introduce macro spin_event_timeout() 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 Acked-by: Geoff Thorpe Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/delay.h | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) (limited to 'arch/powerpc/include/asm/delay.h') diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h index f9200a65c632..1e2eb41fa057 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 + /* * 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 +33,38 @@ 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 each evaluation of + * @condition + * + * The process spins until the condition evaluates to true (non-zero) or the + * timeout elapses. The return value of this macro is the value of + * @condition when the loop terminates. This allows you to determine the cause + * of the loop terminates. If the return value is zero, then you know a + * timeout has occurred. + * + * 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) \ +({ \ + typeof(condition) __ret; \ + unsigned long __loops = tb_ticks_per_usec * timeout; \ + unsigned long __start = get_tbl(); \ + while (!(__ret = (condition)) && (tb_ticks_since(__start) <= __loops)) \ + if (delay) \ + udelay(delay); \ + else \ + cpu_relax(); \ + __ret; \ +}) + #endif /* __KERNEL__ */ #endif /* _ASM_POWERPC_DELAY_H */ -- cgit v1.2.3 From ad9064d5e22a6a24f828dad63c4775c4d7280bd4 Mon Sep 17 00:00:00 2001 From: Grant Likely Date: Mon, 29 Jun 2009 13:40:51 +0000 Subject: powerpc: Fix spin_event_timeout() to be robust over context switches Current implementation of spin_event_timeout can be interrupted by an IRQ or context switch after testing the condition, but before checking the timeout. This can cause the loop to report a timeout when the condition actually became true in the middle. This patch adds one final check of the condition upon exit of the loop if the last test of the condition was still false. Signed-off-by: Grant Likely Acked-by: Timur Tabi Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/delay.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/powerpc/include/asm/delay.h') diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h index 1e2eb41fa057..52e4d54da2a9 100644 --- a/arch/powerpc/include/asm/delay.h +++ b/arch/powerpc/include/asm/delay.h @@ -63,6 +63,8 @@ extern void udelay(unsigned long usecs); udelay(delay); \ else \ cpu_relax(); \ + if (!__ret) \ + __ret = (condition); \ __ret; \ }) -- cgit v1.2.3