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From: Will Deacon <will.deacon@arm.com>
To: Tero Kristo <t-kristo@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>,
	Rajendra Nayak <rnayak@codeaurora.org>,
	Tony Lindgren <tony@atomide.com>,
	Russell King <rmk+kernel@armlinux.org.uk>,
	linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: avoid Cortex-A9 livelock on tight dmb loops
Date: Tue, 10 Apr 2018 16:28:27 +0100	[thread overview]
Message-ID: <20180410152827.GE15514@arm.com> (raw)
In-Reply-To: <685f80e3-30b3-8806-b81c-8de456507001@ti.com>

On Tue, Apr 10, 2018 at 05:12:37PM +0300, Tero Kristo wrote:
> On 10/04/18 16:41, Tony Lindgren wrote:
> >* Russell King <rmk+kernel@armlinux.org.uk> [180410 10:43]:
> >>diff --git a/arch/arm/mach-omap2/prm_common.c b/arch/arm/mach-omap2/prm_common.c
> >>index 021b5a8b9c0a..d4ddc78b2a0b 100644
> >>--- a/arch/arm/mach-omap2/prm_common.c
> >>+++ b/arch/arm/mach-omap2/prm_common.c
> >>@@ -523,7 +523,7 @@ void omap_prm_reset_system(void)
> >>  	prm_ll_data->reset_system();
> >>  	while (1)
> >>-		cpu_relax();
> >>+		cpu_do_idle();
> >>  }
> >
> >Hmm we need to check so the added WFI here does not cause an
> >undesired change to a low power state. Adding Tero to Cc also.
> 
> Generally it is a bad idea to call arbitrary WFI within OMAP architecture,
> as this triggers a PRCM power transition and will most likely cause a hang
> if not controlled properly.
> 
> Has this patch been tested on any platform that supports proper power
> management?

An alternative to WFI would be a DSB, which should avoid unexpected
interactions with power management.

Will

WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: avoid Cortex-A9 livelock on tight dmb loops
Date: Tue, 10 Apr 2018 16:28:27 +0100	[thread overview]
Message-ID: <20180410152827.GE15514@arm.com> (raw)
In-Reply-To: <685f80e3-30b3-8806-b81c-8de456507001@ti.com>

On Tue, Apr 10, 2018 at 05:12:37PM +0300, Tero Kristo wrote:
> On 10/04/18 16:41, Tony Lindgren wrote:
> >* Russell King <rmk+kernel@armlinux.org.uk> [180410 10:43]:
> >>diff --git a/arch/arm/mach-omap2/prm_common.c b/arch/arm/mach-omap2/prm_common.c
> >>index 021b5a8b9c0a..d4ddc78b2a0b 100644
> >>--- a/arch/arm/mach-omap2/prm_common.c
> >>+++ b/arch/arm/mach-omap2/prm_common.c
> >>@@ -523,7 +523,7 @@ void omap_prm_reset_system(void)
> >>  	prm_ll_data->reset_system();
> >>  	while (1)
> >>-		cpu_relax();
> >>+		cpu_do_idle();
> >>  }
> >
> >Hmm we need to check so the added WFI here does not cause an
> >undesired change to a low power state. Adding Tero to Cc also.
> 
> Generally it is a bad idea to call arbitrary WFI within OMAP architecture,
> as this triggers a PRCM power transition and will most likely cause a hang
> if not controlled properly.
> 
> Has this patch been tested on any platform that supports proper power
> management?

An alternative to WFI would be a DSB, which should avoid unexpected
interactions with power management.

Will

  reply	other threads:[~2018-04-10 15:28 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-10 10:41 [PATCH] ARM: avoid Cortex-A9 livelock on tight dmb loops Russell King
2018-04-10 10:41 ` Russell King
2018-04-10 13:41 ` Tony Lindgren
2018-04-10 13:41   ` Tony Lindgren
2018-04-10 14:12   ` Tero Kristo
2018-04-10 14:12     ` Tero Kristo
2018-04-10 15:28     ` Will Deacon [this message]
2018-04-10 15:28       ` Will Deacon
2018-04-11 12:52     ` Russell King - ARM Linux
2018-04-11 12:52       ` Russell King - ARM Linux
2018-04-11 12:57       ` Tero Kristo
2018-04-11 12:57         ` Tero Kristo
2018-04-11 12:59       ` Keerthy
2018-04-11 12:59         ` Keerthy
2018-04-11 13:10         ` Russell King - ARM Linux
2018-04-11 13:10           ` Russell King - ARM Linux
2018-04-11 14:11       ` Tony Lindgren
2018-04-11 14:11         ` Tony Lindgren
2018-04-15 14:08         ` Russell King - ARM Linux
2018-04-15 14:08           ` Russell King - ARM Linux
2018-04-15 15:50           ` Russell King - ARM Linux
2018-04-15 15:50             ` Russell King - ARM Linux

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