[PATCH v2 0/4] pseries-wdt: initial support for H_WATCHDOG-based watchdog timers

[Scott Cheloha <cheloha@linux.ibm.com>]

PAPR v2.12 defines a new hypercall, H_WATCHDOG.  This patch series
adds support for this hypercall to powerpc/pseries kernels and
introduces a new watchdog driver, "pseries-wdt", for the virtual
timers exposed by the hypercall.

This series is preceded by the following:

RFC v1: https://lore.kernel.org/linux-watchdog/20220413165104.179144-1-cheloha@linux.ibm.com/
RFC v2: https://lore.kernel.org/linux-watchdog/20220509174357.5448-1-cheloha@linux.ibm.com/
PATCH v1: https://lore.kernel.org/linux-watchdog/20220520183552.33426-1-cheloha@linux.ibm.com/

Changes of note from PATCH v1:

- Trim down the large comment documenting the H_WATCHDOG hypercall.
  The comment is likely to rot, so remove anything we aren't using
  and anything overly obvious.

- Remove any preprocessor definitions not actually used in the module
  right now.  If we want to use other features offered by the hypercall
  we can add them in later.  They're just clutter until then.

- Simplify the "action" module parameter.  The value is now an index
  into an array of possible timeoutAction values.  This design removes
  the need for the custom get/set methods used in PATCH v1.

  Now we merely need to check that the "action" value is a valid
  index during pseries_wdt_probe().  Easy.

- Make the timeoutAction a member of pseries_wdt, "action".  This
  eliminates the use of a global variable during pseries_wdt_start().

- Use watchdog_init_timeout() idiomatically.  Check its return value
  and error out of pseries_wdt_probe() if it fails.