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

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Date:	Fri, 14 Aug 2015 08:14:52 -0700
From:	santosh shilimkar <santosh.shilimkar@...cle.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Murali Karicheri <m-karicheri2@...com>
Cc:	ssantosh@...nel.org, 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 8/14/2015 7:09 AM, Russell King - ARM Linux wrote:
> On Fri, Aug 14, 2015 at 10:04:41AM -0400, Murali Karicheri wrote:
>> 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?
>
> What causes the abort?  We shouldn't be adding hacks like this to the
> kernel without having the full picture...
>
Indeed. These external aborts are notorious and often hides dangerous
bugs. On OMAP as well many folks burn their had with it till the
interconnect handlers were added to detect those and hunt those
bugs.

In my experience such aborts happen outside ARM subsystem, either in
the interconnect or at the salve targets which are reported over
the ARM bus as async external aborts. And often these errors are
due to bad accesses/wrong accesses/un-clocked accesses at slaves.

Regards,
Santosh

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