linux-kernel - Re: [PATCH] watchdog: mtk: support pre-timeout when the bark irq is available

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Date:   Fri, 9 Apr 2021 21:35:38 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     王擎 <wangqing@...o.com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: mtk: support pre-timeout when the bark irq is
 available

On 4/9/21 8:11 PM, 王擎 wrote:
> 
>> On 4/9/21 7:42 PM, 王擎 wrote:
>>>
>>>> On 4/9/21 2:55 AM, Wang Qing wrote:
>>>>> Use the bark interrupt as the pretimeout notifier if available.
>>>>>
>>>>> By default, the pretimeout notification shall occur one second earlier
>>>>> than the timeout.
>>>>>
>>>>> Signed-off-by: Wang Qing <wangqing@...o.com>
>>>>> ---
>>>>>  drivers/watchdog/mtk_wdt.c | 47 +++++++++++++++++++++++++++++++++++++++++++---
>>>>>  1 file changed, 44 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
>>>>> index 97ca993..8b919cc
>>>>> --- a/drivers/watchdog/mtk_wdt.c
>>>>> +++ b/drivers/watchdog/mtk_wdt.c
>>>>> @@ -25,6 +25,7 @@
>>>>>  #include <linux/reset-controller.h>
>>>>>  #include <linux/types.h>
>>>>>  #include <linux/watchdog.h>
>>>>> +#include <linux/interrupt.h>
>>>>>  
>>>>>  #define WDT_MAX_TIMEOUT		31
>>>>>  #define WDT_MIN_TIMEOUT		1
>>>>> @@ -234,18 +235,35 @@ static int mtk_wdt_start(struct watchdog_device *wdt_dev)
>>>>>  	void __iomem *wdt_base = mtk_wdt->wdt_base;
>>>>>  	int ret;
>>>>>  
>>>>> -	ret = mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
>>>>> +	ret = mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout - wdt_dev->pretimeout);
>>>>
>>>> That looks suspiciously like the real watchdog won't happen at all.
>>>> What will happen if the pretimeout governor is set to none ?
>>>>
>>>> Guenter
>>>>
>>> The pretimeout governor is panic by default. If pretimeout is enabled and the governor is
>>> set to none, it means the timeout behavior does not need to be processed, only printing.
>>>
>>
>> That was not my question. My question was if the real timeout happens in that case.
>>
>> Guenter
>>
> Yes, the real timeout will happen. After WDT timeout, IRQ is sent out instead of 
> reset signal first. In order to ensure that CPU does not get stuck after IRQ is sent out, 
> WDT will time again and send reset signal to reset.
> 

When will that be, or in other words how does the chip know when to time out ?
After all, only a single timeout value is written into the chip. I don't see how
it would know to reset the chip after wdt_dev->timeout.

Guenter