From: "Zeng, Star" <star.zeng@intel.com>
To: Julien Grall <julien.grall@linaro.org>,
Laszlo Ersek <lersek@redhat.com>,
"edk2-devel@lists.01.org" <edk2-devel@lists.01.org>
Cc: "Ni, Ruiyu" <ruiyu.ni@intel.com>, "Zeng, Star" <star.zeng@intel.com>
Subject: Re: [PATCH V2] MdeModulePkg SerialDxe: Handle Timeout change more robustly
Date: Thu, 9 Nov 2017 01:02:00 +0000 [thread overview]
Message-ID: <0C09AFA07DD0434D9E2A0C6AEB0483103B9B3490@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <4fab5c71-d4a9-ee2d-7017-a4c7047713b1@linaro.org>
Pushed at a7fd8452964c1a6ffeee1fe07537cb900c0ccb07.
Thanks for review and test.
Star
-----Original Message-----
From: Julien Grall [mailto:julien.grall@linaro.org]
Sent: Wednesday, November 8, 2017 10:36 PM
To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
Cc: Laszlo Ersek <lersek@redhat.com>; Ni, Ruiyu <ruiyu.ni@intel.com>
Subject: Re: [PATCH V2] MdeModulePkg SerialDxe: Handle Timeout change more robustly
Hi Star,
On 07/11/17 01:36, 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>
Tested-by: Julien Grall <julien.grall@linaro.org>
Cheers,
--
Julien Grall
prev parent reply other threads:[~2017-11-09 0:58 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
2017-11-07 18:31 ` Laszlo Ersek
2017-11-08 14:35 ` Julien Grall
2017-11-09 1:02 ` Zeng, Star [this message]
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