[PATCH] PcAtChipsetPkg AcpiTimerLib: Clear bits [31:24] after reading by IoRead32()

[Star Zeng <star.zeng@intel.com>]

Clear bits [31:24] when reading ACPI timer count by IoRead32(),
also add comments "Note: The library only supports 24Bits ACPI timer" in INF.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c       | 8 ++++----
 PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf | 6 ++++--
 PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf  | 8 +++++---
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
index 020031e3f4a5..67f165ed20ac 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
@@ -162,14 +162,14 @@ InternalAcpiDelay (
     //
     // The target timer count is calculated here
     //
-    Ticks = IoRead32 (Port) + Delay;
+    Ticks = (IoRead32 (Port) & (BIT24 - 1)) + Delay;
     Delay = BIT22;
     //
     // Wait until time out
     // Delay >= 2^23 could not be handled by this function
     // Timer wrap-arounds are handled correctly by this function
     //
-    while (((Ticks - IoRead32 (Port)) & BIT23) == 0) {
+    while (((Ticks - (IoRead32 (Port) & (BIT24 - 1))) & BIT23) == 0) {
       CpuPause ();
     }
   } while (Times-- > 0);
@@ -371,7 +371,7 @@ InternalCalculateTscFrequency (
   // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
   // 363 counts is a calibration time of 101.4 uS.
   //
-  Ticks = IoRead32 (TimerAddr) + 363;
+  Ticks = (IoRead32 (TimerAddr) & (BIT24 - 1)) + 363;
 
   StartTSC = AsmReadTsc ();                                         // Get base value for the TSC
   //
@@ -380,7 +380,7 @@ InternalCalculateTscFrequency (
   // When the current ACPI timer value is greater than 'Ticks',
   // the while loop will exit.
   //
-  while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {
+  while (((Ticks - (IoRead32 (TimerAddr) & (BIT24 - 1))) & BIT23) == 0) {
     CpuPause();
   }
   EndTSC = AsmReadTsc ();                                           // TSC value 101.4 us later
diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf
index 48caebff1354..913fbfe7d30e 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf
@@ -2,9 +2,11 @@
 #  Base ACPI Timer Library
 #
 #  Provides basic timer support using the ACPI timer hardware.  The performance
-#  counter features are provided by the processors time stamp counter. 
+#  counter features are provided by the processors time stamp counter.
 #
-#  Copyright (c) 2013 - 2015, Intel Corporation. All rights reserved.<BR>
+#  Note: The library only supports 24Bits ACPI timer.
+#
+#  Copyright (c) 2013 - 2016, Intel Corporation. All rights reserved.<BR>
 #  This program and the accompanying materials
 #  are licensed and made available under the terms and conditions of the BSD License
 #  which accompanies this distribution.  The full text of the license may be found at
diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf
index 3446c03eda21..33d4970afc57 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf
@@ -2,9 +2,11 @@
 #  DXE ACPI Timer Library
 #
 #  Provides basic timer support using the ACPI timer hardware.  The performance
-#  counter features are provided by the processors time stamp counter. 
+#  counter features are provided by the processors time stamp counter.
 #
-#  Copyright (c) 2013 - 2015, Intel Corporation. All rights reserved.<BR>
+#  Note: The library only supports 24Bits ACPI timer.
+#
+#  Copyright (c) 2013 - 2016, Intel Corporation. All rights reserved.<BR>
 #  This program and the accompanying materials
 #  are licensed and made available under the terms and conditions of the BSD License
 #  which accompanies this distribution.  The full text of the license may be found at
@@ -49,4 +51,4 @@ [Pcd]
   gPcAtChipsetPkgTokenSpaceGuid.PcdAcpiIoPciBarRegisterOffset     ## CONSUMES
   gPcAtChipsetPkgTokenSpaceGuid.PcdAcpiIoPortBaseAddress          ## CONSUMES
   gPcAtChipsetPkgTokenSpaceGuid.PcdAcpiPm1TmrOffset               ## CONSUMES
-  gPcAtChipsetPkgTokenSpaceGuid.PcdAcpiIoPortBaseAddressMask      ## CONSUMES
\ No newline at end of file
+  gPcAtChipsetPkgTokenSpaceGuid.PcdAcpiIoPortBaseAddressMask      ## CONSUMES
-- 
2.7.0.windows.1