From: Laszlo Ersek <lersek@redhat.com>
To: Star Zeng <star.zeng@intel.com>, edk2-devel@lists.01.org
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Subject: Re: [PATCH V2] MdeModulePkg SerialDxe: Handle Timeout change more robustly
Date: Tue, 7 Nov 2017 19:27:51 +0100 [thread overview]
Message-ID: <7752d682-9976-8873-e702-46fb31a49965@redhat.com> (raw)
In-Reply-To: <1510018605-84896-1-git-send-email-star.zeng@intel.com>
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.grall@linaro.org>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Compare against the original parameters
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Star Zeng <star.zeng@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.
> + //
> + 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 <lersek@redhat.com>
Thanks!
Laszlo
next prev parent reply other threads:[~2017-11-07 18:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-07 1:36 [PATCH V2] MdeModulePkg SerialDxe: Handle Timeout change more robustly Star Zeng
2017-11-07 18:27 ` Laszlo Ersek [this message]
2017-11-07 18:31 ` Laszlo Ersek
2017-11-08 14:35 ` Julien Grall
2017-11-09 1:02 ` Zeng, Star
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