ArmPlatformPkg: Updated PL011UartLib.c to not wait indefinitely during read

This patch updates PL011UartLib.c to not wait until the RX buffer
has data in it, but return if the buffer is empty.

Author: artgup

ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c

@@ -435,6 +435,24 @@ PL011UartWrite (
   return NumberOfBytes;
 }
 
+// MU_CHANGE Starts: Do not wait indefinitely for the receive buffer to get filled.
+
+/**
+  Check to see if any data is available to be read from the debug device.
+
+  @retval TRUE       At least one byte of data is available to be read
+  @retval FALSE      No data is available to be read
+
+**/
+BOOLEAN
+EFIAPI
+PL011UartPoll (
+  IN  UINTN  UartBase
+  )
+{
+  return ((MmioRead32 (UartBase + UARTFR) & UART_RX_EMPTY_FLAG_MASK) == 0);
+}
+
 /**
   Read data from serial device and save the data in buffer.
 
@@ -455,28 +473,15 @@ PL011UartRead (
 {
   UINTN  Count;
 
-  for (Count = 0; Count < NumberOfBytes; Count++, Buffer++) {
-    while ((MmioRead32 (UartBase + UARTFR) & UART_RX_EMPTY_FLAG_MASK) != 0) {
-    }
+  // for (Count = 0; Count < NumberOfBytes; Count++, Buffer++) {
+  //   while ((MmioRead32 (UartBase + UARTFR) & UART_RX_EMPTY_FLAG_MASK) != 0) {
+  //   }
 
+  for (Count = 0; (Count < NumberOfBytes) && PL011UartPoll (UartBase); Count++, Buffer++) {
     *Buffer = MmioRead8 (UartBase + UARTDR);
   }
 
-  return NumberOfBytes;
-}
-
-/**
-  Check to see if any data is available to be read from the debug device.
-
-  @retval TRUE       At least one byte of data is available to be read
-  @retval FALSE      No data is available to be read
+  return Count;
 
-**/
-BOOLEAN
-EFIAPI
-PL011UartPoll (
-  IN  UINTN  UartBase
-  )
-{
-  return ((MmioRead32 (UartBase + UARTFR) & UART_RX_EMPTY_FLAG_MASK) == 0);
+  // MU_CHANGE Ends
 }