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    SubjectRe: [PATCH v2 6/7] Watchdog: introduce ARM SBSA watchdog driver
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    Hi Guenter,

    On 24 May 2015 at 04:01, Guenter Roeck <linux@roeck-us.net> wrote:
    > On 05/23/2015 12:40 PM, Timur Tabi wrote:
    > [ ... ]
    >>
    >>
    >> I use emergency_restart(), because the watchdog-api.txt documentation says
    >> this:
    >>
    >> "If userspace fails (RAM error, kernel bug, whatever), the
    >> notifications cease to occur, and the hardware watchdog will reset the
    >> system (causing a reboot) after the timeout occurs."
    >>
    >> Maybe I'm reading this too literally, but to me this means that when the
    >> timeout expires, the system has to reset immediately.
    >>
    >> However, maybe panic() is better, since it can do the same thing and more.
    >>
    >
    > I have a specific requirement at work to have watchdog expiration
    > (not this watchdog, this is different HW) result in a panic, specifically
    > to enable crashdump support and thus post-mortem analysis.
    >
    > I had not thought about this use case myself, and I had always wondered
    > why watchdog driver implementers would choose to call panic() after an
    > interrupt or NMI. But we live and learn, so now I finally understand.
    >
    > In the pretimeout/timeout world, the pretimeout would (typically)
    > result in a panic, and the timeout would result in a reset. So one
    > would set the timer register to 10s for 10s pretimeout and 20s timeout.
    >
    > However, the pretimeout concept assumes that there are two timers
    > which can be set independently. As you had pointed out earlier,
    > and as the specification seems to confirm, that is not the case here.

    Sorry, in Documentation/watchdog/watchdog-api.txt, I can not get the
    info about " the pretimeout concept assumes that there are two timers
    which can be set independently."
    Could you kindly point out where is the assumption.

    I thinks in kernel documentation, that meams "one watchdog has two
    timeout stages", maybe I miss something. Could you help me out?

    > As such, I don't really understand why and how the pretimeout / timeout
    > concept would add any value here and not just make things more
    > complicated than necessary. Maybe I am just missing something.

    If pretimeout concept assumes that there are two timers, I
    misunderstand the "pretimeout", then I will delete the pretimeout
    immediately.

    >
    > Thanks,
    > Guenter
    >



    --
    Best regards,

    Fu Wei
    Software Engineer
    Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
    Ph: +86 21 61221326(direct)
    Ph: +86 186 2020 4684 (mobile)
    Room 1512, Regus One Corporate Avenue,Level 15,
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