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

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Date:	Fri, 4 Mar 2016 14:26:55 +0100
From:	Romain Izard <romain.izard.pro@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
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

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.

-- 
Romain Izard