ACPI / watchdog: Add support for WDAT hardware watchdog

Starting from Intel Skylake the iTCO watchdog timer registers were moved to
reside in the same register space with SMBus host controller.  Not all
needed registers are available though and we need to unhide P2SB (Primary
to Sideband) device briefly to be able to read status of required NO_REBOOT
bit. The i2c-i801.c SMBus driver used to handle this and creation of the
iTCO watchdog platform device.

Windows, on the other hand, does not use the iTCO watchdog hardware
directly even if it is available. Instead it relies on ACPI Watchdog Action
Table (WDAT) table to describe the watchdog hardware to the OS. This table
contains necessary information about the the hardware and also set of
actions which are executed by a driver as needed.

This patch implements a new watchdog driver that takes advantage of the
ACPI WDAT table. We split the functionality into two parts: first part
enumerates the WDAT table and if found, populates resources and creates
platform device for the actual driver. The second part is the driver
itself.

The reason for the split is that this way we can make the driver itself to
be a module and loaded automatically if the WDAT table is found. Otherwise
the module is not loaded.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 1bffe006ca9a..50dbaa805658 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -152,6 +152,19 @@ config TANGOX_WATCHDOG
 
           This driver can be built as a module. The module name is tangox_wdt.
 
+config WDAT_WDT
+        tristate "ACPI Watchdog Action Table (WDAT)"
+        depends on ACPI
+        select ACPI_WATCHDOG
+        help
+          This driver adds support for systems with ACPI Watchdog Action
+          Table (WDAT) table. Servers typically have this but it can be
+          found on some desktop machines as well. This driver will take
+          over the native iTCO watchdog driver found on many Intel CPUs.
+
+          To compile this driver as module, choose M here: the module will
+          be called wdat_wdt.
+
 config WM831X_WATCHDOG
         tristate "WM831x watchdog"
         depends on MFD_WM831X