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+Last reviewed: 06/02/2009
+
+                     HP iLO2 NMI Watchdog Driver
+              NMI sourcing for iLO2 based ProLiant Servers
+                     Documentation and Driver by
+              Thomas Mingarelli <thomas.mingarelli@hp.com>
+
+ The HP iLO2 NMI Watchdog driver is a kernel module that provides basic
+ watchdog functionality and the added benefit of NMI sourcing. Both the
+ watchdog functionality and the NMI sourcing capability need to be enabled
+ by the user. Remember that the two modes are not dependant on one another.
+ A user can have the NMI sourcing without the watchdog timer and vice-versa.
+
+ Watchdog functionality is enabled like any other common watchdog driver. That
+ is, an application needs to be started that kicks off the watchdog timer. A
+ basic application exists in the Documentation/watchdog/src directory called
+ watchdog-test.c. Simply compile the C file and kick it off. If the system
+ gets into a bad state and hangs, the HP ProLiant iLO 2 timer register will
+ not be updated in a timely fashion and a hardware system reset (also known as
+ an Automatic Server Recovery (ASR)) event will occur.
+
+ The hpwdt driver also has four (4) module parameters. They are the following:
+
+ soft_margin - allows the user to set the watchdog timer value
+ allow_kdump - allows the user to save off a kernel dump image after an NMI
+ nowayout    - basic watchdog parameter that does not allow the timer to
+               be restarted or an impending ASR to be escaped.
+ priority    - determines whether or not the hpwdt driver is first on the
+               die_notify list to handle NMIs or last. The default value
+               for this module parameter is 0 or LAST. If the user wants to
+               enable NMI sourcing then reload the hpwdt driver with
+               priority=1 (and boot with nmi_watchdog=0).
+
+ NOTE: More information about watchdog drivers in general, including the ioctl
+       interface to /dev/watchdog can be found in
+       Documentation/watchdog/watchdog-api.txt and Documentation/IPMI.txt.
+
+ The priority parameter was introduced due to other kernel software that relied
+ on handling NMIs (like oprofile). Keeping hpwdt's priority at 0 (or LAST)
+ enables the users of NMIs for non critical events to be work as expected.
+
+ The NMI sourcing capability is disabled by default due to the inability to
+ distinguish between "NMI Watchdog Ticks" and "HW generated NMI events" in the
+ Linux kernel. What this means is that the hpwdt nmi handler code is called
+ each time the NMI signal fires off. This could amount to several thousands of
+ NMIs in a matter of seconds. If a user sees the Linux kernel's "dazed and
+ confused" message in the logs or if the system gets into a hung state, then
+ the hpwdt driver can be reloaded with the "priority" module parameter set
+ (priority=1).
+
+ 1. If the kernel has not been booted with nmi_watchdog turned off then
+    edit /boot/grub/menu.lst and place the nmi_watchdog=0 at the end of the
+    currently booting kernel line.
+ 2. reboot the sever
+ 3. Once the system comes up perform a rmmod hpwdt
+ 4. insmod /lib/modules/`uname -r`/kernel/drivers/char/watchdog/hpwdt.ko priority=1
+
+ Now, the hpwdt can successfully receive and source the NMI and provide a log
+ message that details the reason for the NMI (as determined by the HP BIOS).
+
+ Below is a list of NMIs the HP BIOS understands along with the associated
+ code (reason):
+
+	No source found                00h
+
+	Uncorrectable Memory Error     01h
+
+	ASR NMI                        1Bh
+
+	PCI Parity Error               20h
+
+	NMI Button Press               27h
+
+	SB_BUS_NMI                     28h
+
+	ILO Doorbell NMI               29h
+
+	ILO IOP NMI                    2Ah
+
+	ILO Watchdog NMI               2Bh
+
+	Proc Throt NMI                 2Ch
+
+	Front Side Bus NMI             2Dh
+
+	PCI Express Error              2Fh
+
+	DMA controller NMI             30h
+
+	Hypertransport/CSI Error       31h
+
+
+
+ -- Tom Mingarelli
+    (thomas.mingarelli@hp.com)