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    SubjectRe: [PATCH v1] watchdog: sama5d4_wdt: Reset delay on start
    On Thu, Mar 03, 2016 at 01:53:47PM +0100, Romain Izard wrote:
    > Hi Guenter,
    >
    > 2016-03-03 13:10 GMT+01:00 Guenter Roeck <linux@roeck-us.net>:
    > > On 03/03/2016 02:29 AM, 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
    > >>
    > >> Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
    > >
    > >
    > > Subject might better read "ping watchdog on start" or similar.
    > >
    > OK. I'll change it for a v2.
    >
    > > Does the watchdog have to be pinged before it is enabled ? I am a bit
    > > concerned that there may still be a 125 uS window during which the
    > > system could restart.
    > >
    >
    > According to the SAMA5D2 & SAMA5D4 datasheets, the timer ought to be
    > reloaded when the watchdog is enabled by a write in the MR register.
    > Unfortunately, it does not work as described, as I encountered the
    > problem on a SAMA5D2 Xplained board.
    >
    > The 4 clock delay is not in the datasheet either, but without any delay
    > the timer is clearly not reloaded, as my issue stays the same. As there
    > is a required delay before writing to MR after writing to CR, I applied
    > the same type of delay in the reverse case.
    >
    Question is if there is now a 4 clock window where the watchdog can
    still reset the system. Can you reload the timer before enabling
    the watchdog ?

    Thanks,
    Guenter

    > Perhaps Nicolas or Wenyou have more information on this.
    >
    > Best regards,
    > --
    > Romain Izard

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