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

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Date:	Fri, 4 Mar 2016 16:26:59 +0100
From:	Romain Izard <romain.izard.pro@...il.com>
To:	Lothar Waßmann <LW@...o-electronics.de>
Cc:	Guenter Roeck <linux@...ck-us.net>, linux-watchdog@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yang, Wenyou" <wenyou.yang@...el.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1] watchdog: sama5d4_wdt: Reset delay on start

Hi Lothar,

2016-03-04 15:59 GMT+01:00 Lothar Waßmann <LW@...o-electronics.de>:
>> >>>>> 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 ?
>>

> Are you aware of the Notes in the SAMA5D4 Reference Manual (Chapter
> 19.5.2 Watchdog Timer Mode Register):
>
> |Note: The first write access prevents any further modification of
> |      the value of this register. Read accesses remain possible.
> |Note: The WDD and WDV values must not be modified within three slow
> |      clock periods following a restart of the watchdog performed by
> |      a write access in WDT_CR. Any modification will cause the watchdog
> |      to trigger an end of period earlier than expected.

This text is valid for older versions of the Watchdog controller, found
in AT91SAM9 and SAMA5D3 chips. But SAMA5D4 & SAMA5D2 have a newer
revision, which supports multiple writes to the MR register.

Are you sure about your datasheet? I have this in the latest version
found on Atmel's site.

> Atmel-11238B-ATARM-SAMA5D4-Datasheet_24-Aug-15
> Section 18.5.2
>
> Note: Write access to this register has no effect if the LOCKMR
>       command is issued in WDT_CR (unlocked on hardware reset).
> Note: The WDT_MR register values must not be modified within three slow
>       clock periods following a restart of the watchdog performed by
>       a write access in WDT_CR. Any modification will cause the watchdog
>       to trigger an end of period earlier than expected.
>

It matches the comments from Wenyou when he committed the sama5d4
watchdog driver to replace the existing at91sam9 watchdog.

Best regards,
-- 
Romain Izard