Last reviewed: 19/01/2012

          Intel_SCU 0.2:  An Intel SCU IOH Based Watchdog Device
                          for Intel part #(s):
                            - AF82MP20 PCH
           Documentation and Driver by Yann Puech and Mark Allyn
             <yannx.puech@intel.com> <mark.a.allyn@intel.com>

Principle
=========

This watchdog device is handled throught external timer 7 of the SCU.
The timer timeout is defined here to allow the watchdog daemon to write
sometimes to the watchdog device. We use this non standard technique because
the timer used for the watchdog is stopped when the platform enters C6 or
higher.

Here is depicted the time line of the watchdog timer:

0s                         50s        60s           75s (*)
|___________________________|__________|_____________|
|<----- timer_timeout ----->|<schedule>|<pre_timeout>|
|<--------------------- timeout -------------------->|

(*) The given values are default ones and can be overridden using ioctl.

timer_timeout: The daemon is waiting for MSI #7
schedule:      The daemon will write to the device when scheduled
pre_timeout:   This range is reached if the device has not been kicked by the
               daemon (so the system is down). We are going to dump kernel
               stacks and CPU regs.
timeout:       When the timer expires, the platform issues a cold_reset.


module params
=============

Production
----------
  pre_timeout:   accessor for the pre timeout
  timeout:       accessor for the timeout
  timer_timeout: accessor for the timer timeout

debug purpose
-------------
  disable_kernel_watchdog: disable the watchdog at boot time (useful with gdb)
  reset_on_release:        avoid to reset straight away after killing the daemon
  kicking_active:          disable the kicking at low level (so a cold reset will
                           occur soon)

ioctl
=====

standard
--------

  WDIOC_GETSUPPORT:
  WDIOC_GETSTATUS:
  WDIOC_GETBOOTSTATUS:
  WDIOC_KEEPALIVE:
  WDIOC_SETPRETIMEOUT:
  WDIOC_SETTIMEOUT:
  WDIOC_GETTIMEOUT:
  WDIOC_SETOPTIONS:
    WDIOS_DISABLECARD
    WDIOS_ENABLECARD

custom
------
  WDIOC_SETTIMERTIMEOUT: sets the timeout of the timer for deblocking the daemon.