[PATCH v1] watchdog: sama5d4_wdt: Reset delay on start

[LW@KARO-electronics.de (Lothar Waßmann)]

Hi,

On Fri, 4 Mar 2016 16:26:59 +0100 Romain Izard wrote:
> Hi Lothar,
> 
> 2016-03-04 15:59 GMT+01:00 Lothar Wa?mann <LW@karo-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
> >
OK, I obviously had an outdated Manual.


Lothar Wa?mann