oops, forgot to write down my only comment:
On 11/07/17 19:27, Laszlo Ersek wrote:
> On 11/07/17 02:36, Star Zeng wrote:
>> https://lists.01.org/pipermail/edk2-devel/2017-October/016479.html
>> reported "Xen Console input very slow in recent UEFI" that appears
>> after 4cf3f37c87ba1f9d58072444bd735e40e4779e70 "MdeModulePkg
>> SerialDxe: Process timeout consistently in SerialRead".
>>
>> Julien did more debugging and find out the following is happening in
>> TerminalConInTimerHandler (MdeModulePkg/Universal/Console/TerminalDxe)
>> when a character is received:
>> 1) GetControl will return EFI_SERIAL_INPUT_BUFFER_EMPTY unset
>> => Entering in the loop to fetch character from the serial
>> 2) GetOneKeyFromSerial()
>> => Return directly with the character read
>> 3) Looping as the fifo is not full and no error
>> 4) GetOneKeyFromSerial() -> SerialRead()
>> => No more character so SerialPortPoll() will return FALSE and loop
>> until timeout
>> => Return EFI_TIMEOUT
>> 5) Exiting the loop from TerminalConInTimerHandler
>> 6) Characters are printed
>>
>> After some investigation, I found it is related to the Timeout value.
>>
>> The Timeout is 1000000 (1s) by default to follow UEFI spec.
>> And the Terminal driver will recalculate and set the Timeout value
>> based on the properties of UART in TerminalDriverBindingStart()/
>> TerminalConInTimerHandler().
>>
>> SerialInTimeOut = 0;
>> if (Mode->BaudRate != 0) {
>> //
>> // According to BAUD rate to calculate the timeout value.
>> //
>> SerialInTimeOut = (1 + Mode->DataBits + Mode->StopBits) *
>> 2 * 1000000 / (UINTN) Mode->BaudRate;
>> }
>>
>> For example, based on the PCD values of PcdUartDefaultBaudRate,
>> PcdUartDefaultDataBits and PcdUartDefaultStopBits, SerialInTimeOut =
>> (1 + 8 + 1) * 2 * 1000000 / (UINTN) 115200 = 173 (us).
>>
>> When SerialDxe is used,
>> TerminalDriverBindingStart()/TerminalConInTimerHandler() ->
>> SerialIo->SetAttributes() ->
>> SerialSetAttributes() ->
>> SerialPortSetAttributes()
>>
>> Some implementations of SerialPortSetAttributes() could handle the
>> input parameters and return RETURN_SUCCESS, for example
>> BaseSerialPortLib16550, then Timeout value will be changed to 173 (us),
>> no "slow down" will be observed.
>> But some implementations of SerialPortSetAttributes() just return
>> RETURN_UNSUPPORTED, for example XenConsoleSerialPortLib, then Timeout
>> value will be not changed and kept 1000000 (1s), "slow down" will be
>> observed.
>>
>> SerialPortLib instance can be enhanced to
>> 1. Handle the input parameters and return status accordingly instead of
>> just returning RETURN_UNSUPPORTED in SerialPortSetAttributes().
>> 2. Just return RETURN_SUCCESS instead of RETURN_UNSUPPORTED in
>> SerialPortSetAttributes() if the instance does not care the input
>> parameters at all.
>>
>> And SerialDxe can also be enhanced like this patch to be more robust
>> to handle Timeout change.
>>
>> Cc: Julien Grall <julien.gr...@linaro.org>
>> Cc: Laszlo Ersek <ler...@redhat.com>
>> Cc: Ruiyu Ni <ruiyu...@intel.com>
>> Compare against the original parameters
>> Suggested-by: Laszlo Ersek <ler...@redhat.com>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Star Zeng <star.z...@intel.com>
>>
>> V2: Compare against the original parameters
>> ---
>> MdeModulePkg/Universal/SerialDxe/SerialIo.c | 45
>> +++++++++++++++++++++++++++--
>> 1 file changed, 42 insertions(+), 3 deletions(-)
>>
>> diff --git a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
>> b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
>> index ebcd92726314..5be77e7acfb0 100644
>> --- a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
>> +++ b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
>> @@ -280,12 +280,51 @@ SerialSetAttributes (
>> IN EFI_STOP_BITS_TYPE StopBits
>> )
>> {
>> - EFI_STATUS Status;
>> - EFI_TPL Tpl;
>> + EFI_STATUS Status;
>> + EFI_TPL Tpl;
>> + UINT64 OriginalBaudRate;
>> + UINT32 OriginalReceiveFifoDepth;
>> + UINT32 OriginalTimeout;
>> + EFI_PARITY_TYPE OriginalParity;
>> + UINT8 OriginalDataBits;
>> + EFI_STOP_BITS_TYPE OriginalStopBits;
>>
>> + //
>> + // Preserve the original input values in case
>> + // SerialPortSetAttributes() updates the input/output parameters even on
>> error.
This line is 81 characters long; for better edk2 style conformance,
please consider wrapping it, before you push the patch.
Thanks!
Laszlo
>> + //
>> + OriginalBaudRate = BaudRate;
>> + OriginalReceiveFifoDepth = ReceiveFifoDepth;
>> + OriginalTimeout = Timeout;
>> + OriginalParity = Parity;
>> + OriginalDataBits = DataBits;
>> + OriginalStopBits = StopBits;
>> Status = SerialPortSetAttributes (&BaudRate, &ReceiveFifoDepth, &Timeout,
>> &Parity, &DataBits, &StopBits);
>> if (EFI_ERROR (Status)) {
>> - return Status;
>> + //
>> + // If it is just to set Timeout value and unsupported is returned,
>> + // do not return error.
>> + //
>> + if ((Status == EFI_UNSUPPORTED) &&
>> + (This->Mode->Timeout != OriginalTimeout) &&
>> + (This->Mode->ReceiveFifoDepth == OriginalReceiveFifoDepth) &&
>> + (This->Mode->BaudRate == OriginalBaudRate) &&
>> + (This->Mode->DataBits == (UINT32) OriginalDataBits) &&
>> + (This->Mode->Parity == (UINT32) OriginalParity) &&
>> + (This->Mode->StopBits == (UINT32) OriginalStopBits)) {
>> + //
>> + // Restore to the original input values.
>> + //
>> + BaudRate = OriginalBaudRate;
>> + ReceiveFifoDepth = OriginalReceiveFifoDepth;
>> + Timeout = OriginalTimeout;
>> + Parity = OriginalParity;
>> + DataBits = OriginalDataBits;
>> + StopBits = OriginalStopBits;
>> + Status = EFI_SUCCESS;
>> + } else {
>> + return Status;
>> + }
>> }
>>
>> //
>>
>
> Reviewed-by: Laszlo Ersek <ler...@redhat.com>
>
> Thanks!
> Laszlo
>
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