PcAtChipsetPkg: Use DV bit to stop the RTC first when changing the time

Legacy BIOS design sets only the Update Cycle Inhibit (SET) bit when
changing the RTC time. Update Cycle Inhibit Bit may not be supported
by the backend device (Common I2C RTC device). It could add Division
Chain Select (DV) bit to stop the RTC first (Write to 0x07), Changing
the RTC time and then Set the DV bit back.

Signed-off-by: Di Zhang <di.zhang@intel.com>

Author: chenlin3

PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c

@@ -561,6 +561,7 @@ PcRtcSetTime (
 {
   EFI_STATUS      Status;
   EFI_TIME        RtcTime;
+  RTC_REGISTER_A  RegisterA;
   RTC_REGISTER_B  RegisterB;
   UINT32          TimerVar;
 
@@ -638,6 +639,11 @@ PcRtcSetTime (
   RegisterB.Bits.Set = 1;
   RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
 
+  RegisterA.Data = RtcRead (RTC_ADDRESS_REGISTER_A);
+  //
+  // Set Divider in Reset status, RTC stops
+  //
+  RtcWrite (RTC_ADDRESS_REGISTER_A, RegisterA.Data | RTC_DIV_RESET);
   //
   // Store the century value to RTC before converting to BCD format.
   //
@@ -660,6 +666,10 @@ PcRtcSetTime (
   RegisterB.Bits.Set = 0;
   RtcWrite (RTC_ADDRESS_REGISTER_B, RegisterB.Data);
 
+  //
+  // Restore Divider status
+  //
+  RtcWrite (RTC_ADDRESS_REGISTER_A, RegisterA.Data);
   //
   // Release RTC Lock.
   //

PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.h

@@ -70,6 +70,7 @@ extern PC_RTC_MODULE_GLOBALS  mModuleGlobal;
 //
 // Register A
 //
+#define RTC_DIV_RESET  0x70
 typedef struct {
   UINT8    Rs  : 4; // Rate Selection Bits
   UINT8    Dv  : 3; // Divisor