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

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Date:	Mon, 17 Aug 2015 10:11:11 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	Lucas Stach <l.stach@...gutronix.de>
CC:	<ssantosh@...nel.org>, <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: keystone: add a work around to handle asynchronous
 external abort

On 08/14/2015 10:11 AM, Lucas Stach wrote:
> Am Freitag, den 14.08.2015, 10:04 -0400 schrieb Murali Karicheri:
>> On 08/11/2015 03:13 PM, Murali Karicheri wrote:
>>> Currently on some devices, an asynchronous external abort exception
>>> happens during boot up when exception handlers are enabled in kernel
>>> before switching to user space. This patch adds a workaround to handle
>>> this once during boot. Many customers are already using this
>>> with out any issues and is required to workaround the above issue.
>>>
>>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>> ---
>>>    arch/arm/mach-keystone/keystone.c | 26 ++++++++++++++++++++++++++
>>>    1 file changed, 26 insertions(+)
>>>
>>> diff --git a/arch/arm/mach-keystone/keystone.c b/arch/arm/mach-keystone/keystone.c
>>> index e2880105..c1d0fe5 100644
>>> --- a/arch/arm/mach-keystone/keystone.c
>>> +++ b/arch/arm/mach-keystone/keystone.c
>>> @@ -15,6 +15,7 @@
>>>    #include <linux/of_platform.h>
>>>    #include <linux/of_address.h>
>>>    #include <linux/memblock.h>
>>> +#include <linux/signal.h>
>>>
>>>    #include <asm/setup.h>
>>>    #include <asm/mach/map.h>
>>> @@ -52,6 +53,24 @@ static struct notifier_block platform_nb = {
>>>    	.notifier_call = keystone_platform_notifier,
>>>    };
>>>
>>> +static bool ignore_first = true;
>>> +static int keystone_async_ext_abort_fault(unsigned long addr, unsigned int fsr,
>>> +					  struct pt_regs *regs)
>>> +{
>>> +	/*
>>> +	 * if first time, ignore this as this is a asynchronous external abort
>>> +	 * happening only some devices that couldn't be root caused and we add
>>> +	 * this work around to handle this first time.
>>> +	 */
>>> +	if (ignore_first) {
>>> +		ignore_first = false;
>>> +		return 0;
>>> +	}
>>> +
>>> +	/* Subsequent ones should be handled as fault */
>>> +	return 1;
>>> +}
>>> +
>>>    static void __init keystone_init(void)
>>>    {
>>>    	if (PHYS_OFFSET >= KEYSTONE_HIGH_PHYS_START) {
>>> @@ -61,6 +80,13 @@ static void __init keystone_init(void)
>>>    	}
>>>    	keystone_pm_runtime_init();
>>>    	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
>>> +
>>> +	/*
>>> +	 * Add a one time exception handler to catch asynchronous external
>>> +	 * abort
>>> +	 */
>>> +	hook_fault_code(17, keystone_async_ext_abort_fault, SIGBUS, 0,
>>> +			"async external abort handler");
>>>    }
>>>
>>>    static phys_addr_t keystone_virt_to_idmap(unsigned long x)
>>>
>> Can this be applied if it looks good?
>>
> The keystone PCIe host driver already hooks the same fault code. Those
> hooks are no chain, but a simple pointer, so one of those handlers is
> going to loose out.
>
> This likely isn't what you intended.
You are right. I will try to debug this further based on your patch and 
as per RMK's suggestion.

Thanks and regards,

Murali
>
> Regards,
> Lucas
>


-- 
Murali Karicheri
Linux Kernel, Keystone
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