linux-kernel - Re: [PATCH] ARM: keystone: add a work around to handle asynchronous external abort

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Message-ID: <55CE63BD.2060107@ti.com>
Date:	Fri, 14 Aug 2015 17:55:09 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	Lucas Stach <l.stach@...gutronix.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <ssantosh@...nel.org>
Subject: Re: [PATCH] ARM: keystone: add a work around to handle asynchronous
 external abort

On 08/14/2015 10:20 AM, Lucas Stach wrote:
> Hi Russell,
>
> Am Freitag, den 14.08.2015, 15:09 +0100 schrieb Russell King - ARM
> Linux:
>
> [...]
>
>>
>> What causes the abort?  We shouldn't be adding hacks like this to the
>> kernel without having the full picture...
>>
>
> some of the issues with tracking down such imprecise external aborts are
> due to the fact that we only enable the signaling of those aborts on
> entering the user-space. So the first schedule() crashes on the previous
> dangling abort.
>
> I'm carrying this patch locally to enable imprecise aborts much earlier
> in the boot process. I think it has already been on the list some times,
> but apparently it has fallen through the cracks. If you agree that this
> is the right thing to do I can do a proper repost.
Lucas,

Would you mind sharing the code? Does that help in root causing where it 
actually happens? I have spend considerable time debugging this, but so 
far not successful.

Murali
>
> Regards,
> Lucas
>
> ---------------------->8---------------------------------------------
>>>From bb9117d94cc2f1061dc364f42c446ccd9191e869 Mon Sep 17 00:00:00 2001
> From: Lucas Stach <l.stach@...gutronix.de>
> Date: Thu, 19 Feb 2015 18:12:50 +0100
> Subject: [PATCH] ARM: Add imprecise abort enable/disable macro
>
> This patch adds imprecise abort enable/disable macros.
> It also enables imprecise aborts when starting kernel.
>
> Changes in v2:
> Only ARMv6 and later have CPSR.A bit. On earlier CPUs,
> and ARMv7M this should be a no-op.
>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
> ---
> lst: rebased on v3.19
> ---
>   arch/arm/include/asm/irqflags.h | 10 ++++++++++
>   arch/arm/kernel/smp.c           |  1 +
>   arch/arm/kernel/traps.c         |  4 ++++
>   3 files changed, 15 insertions(+)
>
> diff --git a/arch/arm/include/asm/irqflags.h
> b/arch/arm/include/asm/irqflags.h
> index 3b763d6652a0..8301f875564e 100644
> --- a/arch/arm/include/asm/irqflags.h
> +++ b/arch/arm/include/asm/irqflags.h
> @@ -51,6 +51,14 @@ static inline void arch_local_irq_disable(void)
>
>   #define local_fiq_enable()  __asm__("cpsie f   @ __stf" : : : "memory",
> "cc")
>   #define local_fiq_disable() __asm__("cpsid f   @ __clf" : : : "memory",
> "cc")
> +
> +#ifndef CONFIG_CPU_V7M
> +#define local_abt_enable()  __asm__("cpsie a   @ __sta" : : : "memory",
> "cc")
> +#define local_abt_disable() __asm__("cpsid a   @ __cla" : : : "memory",
> "cc")
> +#else
> +#define local_abt_enable()     do { } while (0)
> +#define local_abt_disable()    do { } while (0)
> +#endif
>   #else
>
>   /*
> @@ -130,6 +138,8 @@ static inline void arch_local_irq_disable(void)
>          : "memory", "cc");                                      \
>          })
>
> +#define local_abt_enable()     do { } while (0)
> +#define local_abt_disable()    do { } while (0)
>   #endif
>
>   /*
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 86ef244c5a24..7b6b93cabef4 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -378,6 +378,7 @@ asmlinkage void secondary_start_kernel(void)
>
>          local_irq_enable();
>          local_fiq_enable();
> +       local_abt_enable();
>
>          /*
>           * OK, it's off to the idle thread for us
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 788e23fe64d8..466726ba9bdb 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -881,6 +881,10 @@ void __init early_trap_init(void *vectors_base)
>
>          flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
>          modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
> +
> +       /* Enable imprecise aborts */
> +       local_abt_enable();
> +
>   #else /* ifndef CONFIG_CPU_V7M */
>          /*
>           * on V7-M there is no need to copy the vector table to a
> dedicated
>


-- 
Murali Karicheri
Linux Kernel, Keystone
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