linux-kernel - Re: [PATCH v1] watchdog: sama5d4

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Date:	Fri, 4 Mar 2016 05:56:20 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Romain Izard <romain.izard.pro@...il.com>
Cc:	"Yang, Wenyou" <wenyou.yang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-watchdog@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: [PATCH v1] watchdog: sama5d4_wdt: Reset delay on start

On 03/04/2016 05:26 AM, Romain Izard wrote:
> 2016-03-04 14:09 GMT+01:00 Guenter Roeck <linux@...ck-us.net>:
>> On 03/04/2016 01:06 AM, Romain Izard wrote:
>>> 2016-03-04 6:23 GMT+01:00 Guenter Roeck <linux@...ck-us.net>:
>>>> On 03/03/2016 05:35 PM, Yang, Wenyou wrote:
>>>>> On 2016/3/3 18:29, Romain Izard wrote:
>>>>>>
>>>>>> If the internal counter is not refreshed when the watchdog is
>>>>>> started for the first time, the watchdog will trigger very
>>>>>> rapidly.  For example, opening /dev/watchdog without writing in it
>>>>>> will immediately trigger a reboot, instead of waiting for the
>>>>>> delay to expire.
>>>>>>
>>>>>> To avoid this problem, reload the timer on opening the watchdog
>>>>>> device.
>>>>>>
>>>>>> Command: "while sleep 5; do echo 1; done > /dev/watchdog" Before:
>>>>>> system reset After: the watchdog runs correctly
>>>>>
>>>>>
>>>>> I didn't reproduce your issue on my side,
>>>>>
>>>>> run the your commands as follows, it works fine,  the system reset
>>>>> doesn't happen.
>>>
>>>
>>> I've just verified with the factory image provided on the SAMA5D2
>>> Xplained board. It does not display this behaviour.
>>>
>>> But the difference is that in the case without the issue, I'm using
>>> the AT91bootstrap SPL, U-Boot, and the kernel from the QSPI chip.
>>> When I have the issue, I have a U-Boot based SPL, U-Boot itself and
>>> the kernel that come from the FAT partition of an SD-Card.
>>>
>>> Userspace does not seem to be involved in the issue, as I can
>>> reproduce it both with my buildroot environment, and the Yocto
>>> environment from the factory image.
>>>
>>>> Different chip revision ? Different chip type ? Different chip
>>>> initialization by ROMMON ?
>>>>
>>>> Can we get exact chip revisions and types for both cases (working
>>>> and not working), and (if it might be relevant) a dump of all
>>>> associated chip registers ?
>>>
>>>
>>>
>>>>> I also check the WDT_MR register before and after enabling
>>>>> watchdog, the WDV and WDD fields are correct.
>>>>>
>>>>> Can you check it again? thank you.
>>>
>>>
>>> Working case:
>>> MR on kernel startup:   0x3fffafff
>>> MR after watchdog init: 0x0fffafff
>>> MR after start:         0x0fff2fff
>>>
>>> Problem case:
>>> MR on kernel startup:   0x00008000
>>> MR after watchdog init: 0x0fffafff
>>> MR after start:         0x0fff2fff
>>>
>>> So this means that the counter reload does not seem to work very well
>>> if WDD/WDV have been set to 0 in the past. The other question is why
>>> does U-Boot (from the Atmel branch based on 2015.1) put this stange
>>> value in this register.
>>>
>>
>> Can you check the value of AT91_WDT_SR ? Maybe it tells us something.
>>
> I didn't report it because it contained 0 at all times. So no information.
>
>> Also, in the error case, can you check if the watchdog times out at all
>> after you applied your patch ?
>
> It times out after 16s as expected, and reboot occurs correctly.
>

Interesting. So it looks like AT91_WDT_WDRSTT has to be set if the timer
values in MR are changed from 0 to another value, or maybe after each
timer value change. Wonder if that should be done in the init function,
after MR is set (with the watchdog disabled).

Thoughts, anyone ?

Thanks,
Guenter