xref: /linux/Documentation/watchdog/hpwdt.rst (revision be239684b18e1cdcafcf8c7face4a2f562c745ad) 
1===========================
2HPE iLO NMI Watchdog Driver
3===========================
4
5for iLO based ProLiant Servers
6==============================
7
8Last reviewed: 08/20/2018
9
10
11 The HPE iLO NMI Watchdog driver is a kernel module that provides basic
12 watchdog functionality and handler for the iLO "Generate NMI to System"
13 virtual button.
14
15 All references to iLO in this document imply it also works on iLO2 and all
16 subsequent generations.
17
18 Watchdog functionality is enabled like any other common watchdog driver. That
19 is, an application needs to be started that kicks off the watchdog timer. A
20 basic application exists in tools/testing/selftests/watchdog/ named
21 watchdog-test.c. Simply compile the C file and kick it off. If the system
22 gets into a bad state and hangs, the HPE ProLiant iLO timer register will
23 not be updated in a timely fashion and a hardware system reset (also known as
24 an Automatic Server Recovery (ASR)) event will occur.
25
26 The hpwdt driver also has the following module parameters:
27
28 ============  ================================================================
29 soft_margin   allows the user to set the watchdog timer value.
30               Default value is 30 seconds.
31 timeout       an alias of soft_margin.
32 pretimeout    allows the user to set the watchdog pretimeout value.
33               This is the number of seconds before timeout when an
34               NMI is delivered to the system. Setting the value to
35               zero disables the pretimeout NMI.
36               Default value is 9 seconds.
37 nowayout      basic watchdog parameter that does not allow the timer to
38               be restarted or an impending ASR to be escaped.
39               Default value is set when compiling the kernel. If it is set
40               to "Y", then there is no way of disabling the watchdog once
41               it has been started.
42 kdumptimeout  Minimum timeout in seconds to apply upon receipt of an NMI
43               before calling panic. (-1) disables the watchdog.  When value
44               is > 0, the timer is reprogrammed with the greater of
45               value or current timeout value.
46 ============  ================================================================
47
48 NOTE:
49       More information about watchdog drivers in general, including the ioctl
50       interface to /dev/watchdog can be found in
51       Documentation/watchdog/watchdog-api.rst and Documentation/driver-api/ipmi.rst
52
53 Due to limitations in the iLO hardware, the NMI pretimeout if enabled,
54 can only be set to 9 seconds.  Attempts to set pretimeout to other
55 non-zero values will be rounded, possibly to zero.  Users should verify
56 the pretimeout value after attempting to set pretimeout or timeout.
57
58 Upon receipt of an NMI from the iLO, the hpwdt driver will initiate a
59 panic. This is to allow for a crash dump to be collected.  It is incumbent
60 upon the user to have properly configured the system for kdump.
61
62 The default Linux kernel behavior upon panic is to print a kernel tombstone
63 and loop forever.  This is generally not what a watchdog user wants.
64
65 For those wishing to learn more please see:
66	- Documentation/admin-guide/kdump/kdump.rst
67	- Documentation/admin-guide/kernel-parameters.txt (panic=)
68	- Your Linux Distribution specific documentation.
69
70 If the hpwdt does not receive the NMI associated with an expiring timer,
71 the iLO will proceed to reset the system at timeout if the timer hasn't
72 been updated.
73
74--
75
76 The HPE iLO NMI Watchdog Driver and documentation were originally developed
77 by Tom Mingarelli.
78