[PATCH v3 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>
Reviewed-by: Star Zeng <star.zeng@intel.com>

---

    Star, I found a prototype for SetAttributes in SerialIo.c as well
    and updated the description there. I decided to keep the Reviewed-by
    even with that change. Let me know whether it is fine for you.

    Changes in v3:
        - Add description of EFI_INVALID_PARAMETER above the prototypes
        for SetAttributes as well.
        - Add Star reviewed-by
---
 MdeModulePkg/Universal/SerialDxe/SerialIo.c | 14 +++++++++-----
 MdePkg/Include/Protocol/SerialIo.h          |  5 +++--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/MdeModulePkg/Universal/SerialDxe/SerialIo.c b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
index 19fc889c25..ee10ec7e05 100644
--- a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
+++ b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
@@ -66,8 +66,9 @@ 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
@@ -264,8 +265,9 @@ 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 +325,10 @@ 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;
     }
   }
 
diff --git a/MdePkg/Include/Protocol/SerialIo.h b/MdePkg/Include/Protocol/SerialIo.h
index 84cb34364d..1263dc4fe9 100644
--- a/MdePkg/Include/Protocol/SerialIo.h
+++ b/MdePkg/Include/Protocol/SerialIo.h
@@ -125,8 +125,9 @@ EFI_STATUS
                            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.
 
 **/
 typedef
-- 
2.11.0