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 dependent 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)