[PATCH v3] PcAtChipsetPkg: Change the flow of PcRtcInit()

["Zhuoran Chao" <zhuoran.chao@intel.com>]

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3913

The original flow of PcRtcInit() is like:
1. Guarantee atomic accesses to the RTC time registers and
   read out the value.
2. Program RTC register B. (adopt 12h mode or 24h mode. Current
   bios code sets RTC to 24h mode by default).
3. Then function ConvertRtcTimeToEfiTime converts the RTC time
   value to their 24h mode by checking the hour format bit
   (1:24h mode,0:12h mode).
And here lies the problem: Step3 will fail to adjust the value
if Step2 already sets RTC to 24h mode. The hour value in 12h mode
will not be converted to its 24h mode.
The solution is to program RTC register B a little later when all
the original RTC registers' value is retrieved, adjusted
and validated.

ConvertRtcTimeToEfiTime is modified to be more robust.

Cc: Ray Ni <ray.ni@intel.com>

Signed-off-by: Zhuoran Chao <zhuoran.chao@intel.com>
---
 .../PcatRealTimeClockRuntimeDxe/PcRtc.c       | 29 ++++++++++---------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c b/PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c
index 0fbfa4bcee..9242a2e826 100644
--- a/PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c
+++ b/PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c
@@ -269,13 +269,6 @@ PcRtcInit (
   Time.Month  = RtcRead (RTC_ADDRESS_MONTH);
   Time.Year   = RtcRead (RTC_ADDRESS_YEAR);
 
-  //
-  // Set RTC configuration after get original time
-  // The value of bit AIE should be reserved.
-  //
-  RegisterB.Data = FixedPcdGet8 (PcdInitialValueRtcRegisterB) | (RegisterB.Data & BIT5);
-  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
-
   //
   // Release RTC Lock.
   //
@@ -330,6 +323,13 @@ PcRtcInit (
     Time.Daylight   = 0;
   }
 
+  //
+  // Set RTC configuration after get original time
+  // The value of bit AIE should be reserved.
+  //
+  RegisterB.Data = FixedPcdGet8 (PcdInitialValueRtcRegisterB) | (RegisterB.Data & BIT5);
+  RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
+
   //
   // Reset time value according to new RTC configuration
   //
@@ -995,13 +995,16 @@ ConvertRtcTimeToEfiTime (
   BOOLEAN  IsPM;
   UINT8    Century;
 
-  if ((Time->Hour & 0x80) != 0) {
-    IsPM = TRUE;
-  } else {
-    IsPM = FALSE;
-  }
+  // IsPM only makes sense for 12-hour format.
+  if (RegisterB.Bits.Mil == 0) {
+    if ((Time->Hour & 0x80) != 0) {
+      IsPM = TRUE;
+    } else {
+      IsPM = FALSE;
+    }
 
-  Time->Hour = (UINT8)(Time->Hour & 0x7f);
+    Time->Hour = (UINT8)(Time->Hour & 0x7f);
+  }
 
   if (RegisterB.Bits.Dm == 0) {
     Time->Year   = CheckAndConvertBcd8ToDecimal8 ((UINT8)Time->Year);
-- 
2.31.1.windows.1