PcAtChipsetPkg: Add MMIO Support to RTC driver

Some virtual machine managers like Kvmtool emulate the MC146818
RTC controller in the MMIO space so that architectures that do
not support I/O Mapped I/O can use the RTC. This patch adds MMIO
support to the RTC controller driver.

The PCD PcdRtcUseMmio has been added to select I/O or MMIO support.
  If PcdRtcUseMmio is:
    TRUE  - Indicates the RTC port registers are in MMIO space.
    FALSE - Indicates the RTC port registers are in I/O space.
            Default is I/O space.

Additionally two new PCDs PcdRtcIndexRegister64 and
PcdRtcTargetRegister64 have been introduced to provide the base
address for the RTC registers in the MMIO space.

When MMIO support is selected (PcdRtcUseMmio == TRUE) the driver
converts the pointers to the RTC MMIO registers so that the
RTC registers are accessible post ExitBootServices.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtcEntry.c

@@ -2,16 +2,23 @@
   Provides Set/Get time operations.
 
 Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2018 - 2020, ARM Limited. All rights reserved.<BR>
 SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#include <Library/DxeServicesTableLib.h>
 #include "PcRtc.h"
 
 PC_RTC_MODULE_GLOBALS  mModuleGlobal;
 
 EFI_HANDLE             mHandle = NULL;
 
+STATIC EFI_EVENT       mVirtualAddrChangeEvent;
+
+UINTN                  mRtcIndexRegister;
+UINTN                  mRtcTargetRegister;
+
 /**
   Returns the current time and date information, and the time-keeping capabilities
   of the hardware platform.
@@ -105,6 +112,30 @@ PcRtcEfiSetWakeupTime (
   return PcRtcSetWakeupTime (Enabled, Time, &mModuleGlobal);
 }
 
+/**
+  Fixup internal data so that EFI can be called in virtual mode.
+  Call the passed in Child Notify event and convert any pointers in
+  lib to virtual mode.
+
+  @param[in]    Event   The Event that is being processed
+  @param[in]    Context Event Context
+**/
+VOID
+EFIAPI
+LibRtcVirtualNotifyEvent (
+  IN EFI_EVENT        Event,
+  IN VOID             *Context
+  )
+{
+  // Only needed if you are going to support the OS calling RTC functions in
+  // virtual mode. You will need to call EfiConvertPointer (). To convert any
+  // stored physical addresses to virtual address. After the OS transitions to
+  // calling in virtual mode, all future runtime calls will be made in virtual
+  // mode.
+  EfiConvertPointer (0x0, (VOID**)&mRtcIndexRegister);
+  EfiConvertPointer (0x0, (VOID**)&mRtcTargetRegister);
+}
+
 /**
   The user Entry Point for PcRTC module.
 
@@ -131,6 +162,11 @@ InitializePcRtc (
   EfiInitializeLock (&mModuleGlobal.RtcLock, TPL_CALLBACK);
   mModuleGlobal.CenturyRtcAddress = GetCenturyRtcAddress ();
 
+  if (FeaturePcdGet (PcdRtcUseMmio)) {
+    mRtcIndexRegister = (UINTN)PcdGet64 (PcdRtcIndexRegister64);
+    mRtcTargetRegister = (UINTN)PcdGet64 (PcdRtcTargetRegister64);
+  }
+
   Status = PcRtcInit (&mModuleGlobal);
   ASSERT_EFI_ERROR (Status);
 
@@ -165,7 +201,23 @@ InitializePcRtc (
                   NULL,
                   NULL
                   );
-  ASSERT_EFI_ERROR (Status);
+  if (EFI_ERROR (Status)) {
+    ASSERT_EFI_ERROR (Status);
+    return Status;
+  }
+
+  if (FeaturePcdGet (PcdRtcUseMmio)) {
+    // Register for the virtual address change event
+    Status = gBS->CreateEventEx (
+                    EVT_NOTIFY_SIGNAL,
+                    TPL_NOTIFY,
+                    LibRtcVirtualNotifyEvent,
+                    NULL,
+                    &gEfiEventVirtualAddressChangeGuid,
+                    &mVirtualAddrChangeEvent
+                    );
+    ASSERT_EFI_ERROR (Status);
+  }
 
   return Status;
 }