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

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Could you also update the description for EFI_SERIAL_SET_ATTRIBUTES in MdePkg/Include/Protocol/SerialIo.h? That could be done in a separated patch.

+  @retval EFI_INVALID_PARAMETER One or more attributes has an unsupported value.

Thanks,
Star
-----Original Message-----
From: Julien Grall [mailto:julien.grall@linaro.org] 
Sent: Saturday, November 25, 2017 12:20 AM
To: Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>; pankaj.bansal@nxp.com; lersek@redhat.com; leif.lindholm@linaro.org
Cc: edk2-devel@lists.01.org; Julien Grall <julien.grall@linaro.org>
Subject: [PATCH v2 2/3] MdeModulePkg/SerialDxe: Fix return valued in SerialSetAttributes

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

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