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Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range

From Guenter Roeck <linux@roeck-us.net>
Newsgroups linux.kernel
Subject Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range
Date 2016-05-05 18:50 +0200
Message-ID <rvuDo-3mH-7@gated-at.bofh.it> (permalink)
References (5 earlier) <ruM9k-3Bx-17@gated-at.bofh.it> <rv5OG-5wR-3@gated-at.bofh.it> <rv5Ym-5ES-23@gated-at.bofh.it> <rv7ns-6NC-19@gated-at.bofh.it> <rv7GO-7iY-19@gated-at.bofh.it>
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On Wed, May 04, 2016 at 11:17:29AM -0500, Timur Tabi wrote:
> Pratyush Anand wrote:
> >Its unique to SBSA because you have very little timeout here. kexec-tools
> >upstream does not have any mechanism to handle watchdog timeout. Lets say even
> >if we implement a framework there, the best it can do is to ping the watchdog
> >again.
> 
> Ok, so it's more accurate to say that kexec has a minimum watchdog timeout
> requirement.  What happens if the system admin sets the timeout to 5 seconds
> arbitrarily?  The system will reset during kexec, no matter which hardware
> is used.
> 
> This still sounds like a band-aid to me.  We're just assuming that we need a
> timeout of at least 20 seconds to support kexec.  Frankly, this still sounds
> like a problem the kexec developers needs to acknowledge and deal with.
> 
> Still I'm okay with a patch that extends the timeout by programming WCV, but
> it has to be commented as a hack specifically to support kexec because the
> timeout might be too short.  Then Wim can decide whether he supports such
> changes.
> 
I don't even understand how kexec-tools is involved in the first place.
kexec-tools sounds like user space, which should execute _after_ the kernel
and its modules are loaded (assuming modules are loaded from initramfs).
If kexec-tools can somehow ping the watchdog (presumably by writing into
the HW directly), I don't understand why it doesn't simply load the watchdog
driver instead and let the watchdog core handle the heartbeats.

I am really missing something here. How can kexec-tools do anything before
the kernel is loaded ?

Guenter

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Thread

[PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-03 10:30 +0200
  Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-03 14:20 +0200
    Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-03 15:30 +0200
      Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-03 15:50 +0200
        Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-03 16:20 +0200
          Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-03 16:50 +0200
            Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-03 17:10 +0200
  Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-03 15:40 +0200
    Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-03 16:40 +0200
      Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-03 17:10 +0200
        Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-03 18:00 +0200
          Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-03 19:20 +0200
            Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-04 16:20 +0200
              Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-04 16:30 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-04 18:00 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-04 18:20 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-05 18:50 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Pratyush Anand <panand@redhat.com> - 2016-05-05 20:30 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-05 20:30 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-06 01:40 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-06 01:40 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Timur Tabi <timur@codeaurora.org> - 2016-05-06 01:50 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-06 02:20 +0200
                Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range Guenter Roeck <linux@roeck-us.net> - 2016-05-06 02:00 +0200

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