linux-kernel - Re: [PATCH] powerpc/8xx: add system_reset

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Date:   Wed, 7 Sep 2016 07:15:59 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Scott Wood <oss@...error.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/8xx: add system_reset_exception



Le 07/09/2016 à 00:40, Scott Wood a écrit :
> On Mon, 2016-09-05 at 08:42 +0200, Christophe Leroy wrote:
>> When the watchdog is in NMI mode, the system reset interrupt is
>> generated when the watchdog counter expires.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>  arch/powerpc/kernel/head_8xx.S | 2 +-
>>  arch/powerpc/kernel/traps.c    | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
>> index 43ddaae..f7b8007 100644
>> --- a/arch/powerpc/kernel/head_8xx.S
>> +++ b/arch/powerpc/kernel/head_8xx.S
>> @@ -227,7 +227,7 @@ i##n:							
>> 	\
>>  			  ret_from_except)
>>
>>  /* System reset */
>> -	EXCEPTION(0x100, Reset, unknown_exception, EXC_XFER_STD)
>> +	EXCEPTION(0x100, Reset, system_reset_exception, EXC_XFER_STD)
>
> Does this do anything useful beyond what unknown_exception does?  Do you plan
> to have a ppc_md.system_reset_exception callback?
>

Yes that's the plan, having a platform specific callback to take 
emergency actions in order to speed up systemwise recovery, then restart 
the board.

In addition, unknown_exception doesn't show you that the exception comes 
from the NMI watchdog.

Christophe