ArmPkg: Update GenericWatchdogDxe to allow setting full 48-bit offset

The generic watchdog offset register is 48 bits wide, and can be set by
performing two 32-bit writes.

Add support for writing the high 16 bits of the offset register and
update the signature of the WatchdogWriteOffsetRegister function to take
a UINT64 value.

Signed-off-by: Rebecca Cran <rebecca@os.amperecomputing.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdog.h

@@ -1,9 +1,13 @@
 /** @file
 *
+*  Copyright (c) 2023, Ampere Computing LLC. All rights reserved.<BR>
 *  Copyright (c) 2013-2017, ARM Limited. All rights reserved.
 *
 *  SPDX-License-Identifier: BSD-2-Clause-Patent
 *
+*  @par Reference(s):
+*  - Generic Watchdog specification in Arm Base System Architecture 1.0C:
+*    https://developer.arm.com/documentation/den0094/c/
 **/
 
 #ifndef GENERIC_WATCHDOG_H_
@@ -14,12 +18,17 @@
 
 // Control Frame:
 #define GENERIC_WDOG_CONTROL_STATUS_REG      ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x000)
-#define GENERIC_WDOG_OFFSET_REG              ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x008)
+#define GENERIC_WDOG_OFFSET_REG_LOW          ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x008)
+#define GENERIC_WDOG_OFFSET_REG_HIGH         ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x00C)
 #define GENERIC_WDOG_COMPARE_VALUE_REG_LOW   ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x010)
 #define GENERIC_WDOG_COMPARE_VALUE_REG_HIGH  ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0x014)
+#define GENERIC_WDOG_IID_REG                 ((UINTN)FixedPcdGet64 (PcdGenericWatchdogControlBase) + 0xFCC)
 
 // Values of bit 0 of the Control/Status Register
 #define GENERIC_WDOG_ENABLED   1
 #define GENERIC_WDOG_DISABLED  0
 
+#define GENERIC_WDOG_IID_ARCH_REV_SHIFT  16
+#define GENERIC_WDOG_IID_ARCH_REV_MASK   0xF
+
 #endif // GENERIC_WATCHDOG_H_

ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c

@@ -1,5 +1,6 @@
 /** @file
 *
+*  Copyright (c) 2023, Ampere Computing LLC. All rights reserved.<BR>
 *  Copyright (c) 2013-2018, ARM Limited. All rights reserved.
 *
 *  SPDX-License-Identifier: BSD-2-Clause-Patent
@@ -35,16 +36,49 @@ STATIC UINTN  mTimerFrequencyHz = 0;
    It is therefore stored here. 0 means the timer is not running. */
 STATIC UINT64  mNumTimerTicks = 0;
 
+#define MAX_UINT48  0xFFFFFFFFFFFFULL
+
 STATIC EFI_HARDWARE_INTERRUPT2_PROTOCOL  *mInterruptProtocol;
 STATIC EFI_WATCHDOG_TIMER_NOTIFY         mWatchdogNotify;
 
+/**
+  This function returns the maximum watchdog offset register value.
+
+  @retval MAX_UINT32 The watchdog offset register holds a 32-bit value.
+  @retval MAX_UINT48 The watchdog offset register holds a 48-bit value.
+**/
+STATIC
+UINT64
+GetMaxWatchdogOffsetRegisterValue (
+  VOID
+  )
+{
+  UINT64  MaxWatchdogOffsetValue;
+  UINT32  WatchdogIId;
+  UINT8   WatchdogArchRevision;
+
+  WatchdogIId          = MmioRead32 (GENERIC_WDOG_IID_REG);
+  WatchdogArchRevision = (WatchdogIId >> GENERIC_WDOG_IID_ARCH_REV_SHIFT) & GENERIC_WDOG_IID_ARCH_REV_MASK;
+
+  if (WatchdogArchRevision == 0) {
+    MaxWatchdogOffsetValue = MAX_UINT32;
+  } else {
+    MaxWatchdogOffsetValue = MAX_UINT48;
+  }
+
+  return MaxWatchdogOffsetValue;
+}
+
 STATIC
 VOID
 WatchdogWriteOffsetRegister (
-  UINT32  Value
+  UINT64  Value
   )
 {
-  MmioWrite32 (GENERIC_WDOG_OFFSET_REG, Value);
+  MmioWrite32 (GENERIC_WDOG_OFFSET_REG_LOW, Value & MAX_UINT32);
+  if (GetMaxWatchdogOffsetRegisterValue () == MAX_UINT48) {
+    MmioWrite32 (GENERIC_WDOG_OFFSET_REG_HIGH, (Value >> 32) & MAX_UINT16);
+  }
 }
 
 STATIC
@@ -196,7 +230,8 @@ WatchdogSetTimerPeriod (
   IN UINT64                            TimerPeriod          // In 100ns units
   )
 {
-  UINTN  SystemCount;
+  UINTN   SystemCount;
+  UINT64  MaxWatchdogOffsetValue;
 
   // if TimerPeriod is 0, this is a request to stop the watchdog.
   if (TimerPeriod == 0) {
@@ -211,17 +246,18 @@ WatchdogSetTimerPeriod (
   /* If the number of required ticks is greater than the max the watchdog's
      offset register (WOR) can hold, we need to manually compute and set
      the compare register (WCV) */
-  if (mNumTimerTicks > MAX_UINT32) {
+  MaxWatchdogOffsetValue = GetMaxWatchdogOffsetRegisterValue ();
+  if (mNumTimerTicks > MaxWatchdogOffsetValue) {
     /* We need to enable the watchdog *before* writing to the compare register,
        because enabling the watchdog causes an "explicit refresh", which
        clobbers the compare register (WCV). In order to make sure this doesn't
        trigger an interrupt, set the offset to max. */
-    WatchdogWriteOffsetRegister (MAX_UINT32);
+    WatchdogWriteOffsetRegister (MaxWatchdogOffsetValue);
     WatchdogEnable ();
     SystemCount = ArmGenericTimerGetSystemCount ();
     WatchdogWriteCompareRegister (SystemCount + mNumTimerTicks);
   } else {
-    WatchdogWriteOffsetRegister ((UINT32)mNumTimerTicks);
+    WatchdogWriteOffsetRegister (mNumTimerTicks);
     WatchdogEnable ();
   }