From 4cf3f37c87ba1f9d58072444bd735e40e4779e70 Mon Sep 17 00:00:00 2001
From: Star Zeng <star.zeng@intel.com>
Date: Tue, 18 Jul 2017 16:32:16 +0800
Subject: [PATCH] MdeModulePkg SerialDxe: Process timeout consistently in
 SerialRead

https://lists.01.org/pipermail/edk2-devel/2017-July/012385.html
reported the timeout processing in SerialRead is not consistent.

Since SerialPortPoll only checks the status of serial port and
returns immediately, and SerialPortRead does not really implement
a time out mechanism and will always wait for enough input,
it will cause below results:
1. If there is no serial input at all, this interface will return
timeout immediately without any waiting;
2. If there is A characters in serial port FIFO, and caller requires
A+1 characters, it will wait until a new input is coming and timeout
will not really occur.

This patch is to update SerialRead() to check SerialPortPoll() and
read data through SerialPortRead() one byte by one byte, and check
timeout against mSerialIoMode.Timeout if no input.

Cc: Heyi Guo <heyi.guo@linaro.org>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
---
 MdeModulePkg/Universal/SerialDxe/SerialIo.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Universal/SerialDxe/SerialIo.c b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
index d2383e56dd..43d33dba0c 100644
--- a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
+++ b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
@@ -465,11 +465,25 @@ SerialRead (
   )
 {
   UINTN Count;
+  UINTN TimeOut;
 
   Count = 0;
 
-  if (SerialPortPoll ()) {
-    Count = SerialPortRead (Buffer, *BufferSize);
+  while (Count < *BufferSize) {
+    TimeOut = 0;
+    while (TimeOut < mSerialIoMode.Timeout) {
+      if (SerialPortPoll ()) {
+        break;
+      }
+      gBS->Stall (10);
+      TimeOut += 10;
+    }
+    if (TimeOut >= mSerialIoMode.Timeout) {
+      break;
+    }
+    SerialPortRead (Buffer, 1);
+    Count++;
+    Buffer = (VOID *) ((UINT8 *) Buffer + 1);
   }
 
   if (Count != *BufferSize) {