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Add list format so that compiled documentation looks like it was intended to. Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com> Reviewed-by: Guenter Roeck <linux@roeck-us.net> Link: https://lore.kernel.org/r/20230210184247.221134-3-jerry.hoemann@hpe.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
78 lines
3.5 KiB
ReStructuredText
78 lines
3.5 KiB
ReStructuredText
===========================
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HPE iLO NMI Watchdog Driver
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===========================
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for iLO based ProLiant Servers
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==============================
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Last reviewed: 08/20/2018
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The HPE iLO NMI Watchdog driver is a kernel module that provides basic
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watchdog functionality and handler for the iLO "Generate NMI to System"
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virtual button.
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All references to iLO in this document imply it also works on iLO2 and all
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subsequent generations.
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Watchdog functionality is enabled like any other common watchdog driver. That
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is, an application needs to be started that kicks off the watchdog timer. A
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basic application exists in tools/testing/selftests/watchdog/ named
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watchdog-test.c. Simply compile the C file and kick it off. If the system
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gets into a bad state and hangs, the HPE ProLiant iLO timer register will
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not be updated in a timely fashion and a hardware system reset (also known as
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an Automatic Server Recovery (ASR)) event will occur.
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The hpwdt driver also has the following module parameters:
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============ ================================================================
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soft_margin allows the user to set the watchdog timer value.
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Default value is 30 seconds.
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timeout an alias of soft_margin.
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pretimeout allows the user to set the watchdog pretimeout value.
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This is the number of seconds before timeout when an
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NMI is delivered to the system. Setting the value to
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zero disables the pretimeout NMI.
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Default value is 9 seconds.
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nowayout basic watchdog parameter that does not allow the timer to
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be restarted or an impending ASR to be escaped.
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Default value is set when compiling the kernel. If it is set
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to "Y", then there is no way of disabling the watchdog once
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it has been started.
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kdumptimeout Minimum timeout in seconds to apply upon receipt of an NMI
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before calling panic. (-1) disables the watchdog. When value
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is > 0, the timer is reprogrammed with the greater of
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value or current timeout value.
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============ ================================================================
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NOTE:
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More information about watchdog drivers in general, including the ioctl
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interface to /dev/watchdog can be found in
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Documentation/watchdog/watchdog-api.rst and Documentation/driver-api/ipmi.rst
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Due to limitations in the iLO hardware, the NMI pretimeout if enabled,
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can only be set to 9 seconds. Attempts to set pretimeout to other
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non-zero values will be rounded, possibly to zero. Users should verify
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the pretimeout value after attempting to set pretimeout or timeout.
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Upon receipt of an NMI from the iLO, the hpwdt driver will initiate a
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panic. This is to allow for a crash dump to be collected. It is incumbent
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upon the user to have properly configured the system for kdump.
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The default Linux kernel behavior upon panic is to print a kernel tombstone
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and loop forever. This is generally not what a watchdog user wants.
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For those wishing to learn more please see:
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- Documentation/admin-guide/kdump/kdump.rst
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- Documentation/admin-guide/kernel-parameters.txt (panic=)
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- Your Linux Distribution specific documentation.
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If the hpwdt does not receive the NMI associated with an expiring timer,
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the iLO will proceed to reset the system at timeout if the timer hasn't
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been updated.
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--
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The HPE iLO NMI Watchdog Driver and documentation were originally developed
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by Tom Mingarelli.
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