[PATCH v2 1/1] ArmPkg/GenericWatchdogDxe: Split 64bit register write to 2x32bit

[Marcin Wojtas <mw@semihalf.com>]

According to the SBSA specification the Watchdog Compare
Register is split into two separate 32bit registers.
EDK2 code uses a single 64bit transaction to update
them, which can be problematic, depending on the SoC
implementation and could result in an unpredicted behavior.

Fix this by modifying WatchdogWriteCompareRegister routine to
use two consecutive 32bit writes to the Watchdog Compare Register
Low and High, using new dedicated macros.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
---
Changelog v1 -> v2:
- use separate macros for WCV register low and high
- improve commit message
- add Leif's RB

 ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h    | 3 ++-
 ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h
index 9e2aebc..4f42c56 100644
--- a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h
+++ b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h
@@ -20,7 +20,8 @@
 // Control Frame:
 #define GENERIC_WDOG_CONTROL_STATUS_REG       ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x000)
 #define GENERIC_WDOG_OFFSET_REG               ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x008)
-#define GENERIC_WDOG_COMPARE_VALUE_REG        ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x010)
+#define GENERIC_WDOG_COMPARE_VALUE_REG_LOW    ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x010)
+#define GENERIC_WDOG_COMPARE_VALUE_REG_HIGH   ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x014)
 
 // Values of bit 0 of the Control/Status Register
 #define GENERIC_WDOG_ENABLED          1
diff --git a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
index 3180f01..8ccf153 100644
--- a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
+++ b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
@@ -56,7 +56,8 @@ WatchdogWriteCompareRegister (
   UINT64  Value
   )
 {
-  MmioWrite64 (GENERIC_WDOG_COMPARE_VALUE_REG, Value);
+  MmioWrite32 (GENERIC_WDOG_COMPARE_VALUE_REG_LOW, Value & MAX_UINT32);
+  MmioWrite32 (GENERIC_WDOG_COMPARE_VALUE_REG_HIGH, (Value >> 32) & MAX_UINT32);
 }
 
 VOID
-- 
2.7.4