1 =========================== 2 HPE iLO NMI Watchdog Driver 3 =========================== 4 5 for iLO based ProLiant Servers 6 ============================== 7 8 Last 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.
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