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

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Message-ID: <20150814140934.GX7557@n2100.arm.linux.org.uk>
Date:	Fri, 14 Aug 2015 15:09:34 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	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 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...

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