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

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Date:	Fri, 4 Mar 2016 05:09:04 -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 01:06 AM, Romain Izard wrote:
> Hi Wenyou, Guenter,
>
> 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.

Also, in the error case, can you check if the watchdog times out at all
after you applied your patch ?

Thanks,
Guenter

> Best regards,
>