[PATCH v2 2/3] MdeModulePkg/SerialDxe: Fix return valued in SerialSetAttributes

[Julien Grall <julien.grall@linaro.org>]

SerialSetAttributes is meant to match the behavior of the function
EFI_SERIAL_IO_PROTOCOL.SetAttributes() in the UEFI spec (v2.7). This
means the function can only return:
    - EFI_SUCCESS
    - EFI_INVALID_PARAMETER
    - EFI_DEVICE_ERROR

However the function SerialPortSetAttributes may also validly return
EFI_UNSUPPORTED. For instance this is the case of the Xen Console
driver.

EFI_UNSUPPORTED could be also interpreted as "One or more of the attributes
has an unsupported value". So return EFI_INVALID_PARAMETER in that case.

Lastly, to prevent another return slipping in the future, all the errors
but EFI_INVALID_PARAMETERR and EFI_UNSUPPORTED will return
EFI_DEVICE_ERROR.

Contributed-under: Tianocore Contribution Agreement 1.1
Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 MdeModulePkg/Universal/SerialDxe/SerialIo.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Universal/SerialDxe/SerialIo.c b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
index 5946a6e2f3..08b95a4a33 100644
--- a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
+++ b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
@@ -264,8 +264,9 @@ SerialReset (
                            value of DefaultStopBits will use the device's default number of
                            stop bits.
 
-  @retval EFI_SUCCESS      The device was reset.
-  @retval EFI_DEVICE_ERROR The serial device is not functioning correctly.
+  @retval EFI_SUCCESS           The device was reset.
+  @retval EFI_INVALID_PARAMETER One or more attributes has an unsupported value.
+  @retval EFI_DEVICE_ERROR      The serial device is not functioning correctly.
 
 **/
 EFI_STATUS
@@ -323,8 +324,10 @@ SerialSetAttributes (
       DataBits = OriginalDataBits;
       StopBits = OriginalStopBits;
       Status = EFI_SUCCESS;
+    } else if (Status == EFI_INVALID_PARAMETER || Status == EFI_UNSUPPORTED) {
+      return EFI_INVALID_PARAMETER;
     } else {
-      return Status;
+      return EFI_DEVICE_ERROR;
     }
   }
 
-- 
2.11.0