Subject: Re: [PATCH] ppc44x/watchdog: Select WATCHDOG_NOWAYOUT option

From: "Lu.Jiang" <[email-masked]>
Date: Mon, 16 Jul 2012 10:07:30 +0800

于 2012年07月13日 19:50, Kumar Gala 写道:
> On Jul 12, 2012, at 9:44 PM, Jiang Lu wrote:
>
>> On PPC44x core, the WRC(Watchdog-timer Reset Control) field of TCR
>> of timer can not reset by software after set to a non-zero value.
>> Which means software can not reset the timeout behaviour of watchdog timer.
>>
>> This patch selects WATCHDOG_NOWAYOUT option for 44x platforms to
>> indicate the watchdog timer can not be disabled once fired.
>>
>> Signed-off-by: Jiang Lu <[email-masked]>
>> ---
>> drivers/watchdog/Kconfig |    1 +
>> 1 files changed, 1 insertions(+), 0 deletions(-)
> I believe this is not 44x specific, but how Book-E watchdog is architected.
>
>> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
>> index 3709624..41f3dff 100644
>> --- a/drivers/watchdog/Kconfig
>> +++ b/drivers/watchdog/Kconfig
>> @@ -1084,6 +1084,7 @@ config PIKA_WDT
>> config BOOKE_WDT
>> 	tristate "PowerPC Book-E Watchdog Timer"
>> 	depends on BOOKE || 4xx
>> +	select WATCHDOG_NOWAYOUT if 44x
> This should probably be 'select WATCHDOG_NOWAYOUT if BOOKE'

On ppc44x's processor, if we disabled 'WATCHDOG_NOWAYOUT ' option. The 
driver's release routine will try to disable the watchdog , by clearing 
the WIE & WTDP field in TCR.
Since the ppc44x's watch dog can not reset by software, such operation 
only set the timeout value(WDTP) to minimum, and cause the system reboot 
immediately.

I checked ppc 476, 405 & 450's manual, these document said the 
WRC(Watchdog-timer Reset Control) field of TCR of timer
can not reset by software after set to a non-zero value. I think all 
ppc44x core should got same limitation.

While on FSL's platform, we did not met such issue. So I think we should 
select 'WATCHDOG_NOWAYOUT' option for 44x platform.

Regards,
Jiang Lu

>
>> 	---help---
>> 	  Watchdog driver for PowerPC Book-E chips, such as the Freescale
>> 	  MPC85xx SOCs and the IBM PowerPC 440.
>> -- 
>> 1.7.7
>>
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>