From: dirk.behme@de•bosch.com (Dirk Behme)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: fix cpu_relax() in case of doing dmb
Date: Thu, 23 Aug 2012 12:23:45 +0200 [thread overview]
Message-ID: <503604B1.7030207@de.bosch.com> (raw)
In-Reply-To: <1345647138-8815-1-git-send-email-shawn.guo@linaro.org>
On 22.08.2012 16:52, Shawn Guo wrote:
> There is an issue reported on imx6q restart function. The issue is only
> seen with the image building ARMv7 and ARMv6 together, where cpu_relax()
> is define to do dmb. It's been root-caused by Russell as below.
>
> Russell King - ARM Linux wrote:
>> I suspect having this dmb inside cpu_relax() is flooding the
>> interconnects with traffic, which then prevents other CPUs getting
>> a look-in (maybe there's no fairness when it comes to dmb's.
>
> Fix the issue by insert a few NOPs into cpu_relax() where doing dmb.
>
> Cc: <stable@vger•kernel.org>
> Signed-off-by: Shawn Guo <shawn.guo@linaro•org>
Tested on a i.MX6 SabreLite board together with the patch 'ARM: imx6q:
remove imx_src_prepare_restart() call':
Tested-by: Dirk Behme <dirk.behme@de•bosch.com>
Thanks
Dirk
> ---
> arch/arm/include/asm/processor.h | 9 ++++++++-
> 1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
> index 99afa74..7cc67ce 100644
> --- a/arch/arm/include/asm/processor.h
> +++ b/arch/arm/include/asm/processor.h
> @@ -80,7 +80,14 @@ extern void release_thread(struct task_struct *);
> unsigned long get_wchan(struct task_struct *p);
>
> #if __LINUX_ARM_ARCH__ == 6 || defined(CONFIG_ARM_ERRATA_754327)
> -#define cpu_relax() smp_mb()
> +#define cpu_relax() do { \
> + asm("nop"); \
> + asm("nop"); \
> + asm("nop"); \
> + asm("nop"); \
> + asm("nop"); \
> + smp_mb(); \
> + } while (0)
> #else
> #define cpu_relax() barrier()
> #endif
next prev parent reply other threads:[~2012-08-23 10:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 14:52 [PATCH] ARM: fix cpu_relax() in case of doing dmb Shawn Guo
2012-08-23 2:47 ` Hui Wang
2012-08-23 10:23 ` Dirk Behme [this message]
2012-08-23 10:43 ` Will Deacon
2012-08-23 13:58 ` Shawn Guo
2012-08-23 18:31 ` Jon Medhurst (Tixy)
2012-08-24 1:15 ` Shawn Guo
2012-08-24 9:14 ` Jon Medhurst (Tixy)
2012-08-24 1:10 ` Hui Wang
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