Re: MdeModulePkg/SerialDxe: Inconsistent timeout processing in SerialRead

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Star,
Your change looks good.

Thanks/Ray

> -----Original Message-----
> From: Zeng, Star
> Sent: Tuesday, July 18, 2017 4:39 PM
> To: Heyi Guo <heyi.guo@linaro.org>; edk2-devel@lists.01.org; Ni, Ruiyu
> <ruiyu.ni@intel.com>; Laszlo Ersek (lersek@redhat.com)
> <lersek@redhat.com>
> Cc: Zeng, Star <star.zeng@intel.com>
> Subject: RE: [edk2] MdeModulePkg/SerialDxe: Inconsistent timeout
> processing in SerialRead
> 
> Gary,
> SerialDxe is a wrapper of SerialPortLib to produce serial io protocol.
> If let SerialDxe to handle the TimeOut, seemingly it can only check
> SerialPortPoll() and read data by SerialPortRead() one byte by one byte, for
> example like below.
> Do you have any proposed patch?
> 
> Ray and Laszlo,
> Do you have any comments?
> 
> 
> ====================
> debf0d1b85e7a30defd29838abb20a44dd9ec69b
>  MdeModulePkg/Universal/SerialDxe/SerialIo.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
> b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
> index d2383e56dd8f..b05603d7f3b5 100644
> --- a/MdeModulePkg/Universal/SerialDxe/SerialIo.c
> +++ b/MdeModulePkg/Universal/SerialDxe/SerialIo.c
> @@ -465,11 +465,25 @@ SerialRead (
>    )
>  {
>    UINTN Count;
> +  UINTN TimeOut;
> 
>    Count = 0;
> 
> -  if (SerialPortPoll ()) {
> -    Count = SerialPortRead (Buffer, *BufferSize);
> +  while (Count < *BufferSize) {
> +    TimeOut = 0;
> +    while (TimeOut < mSerialIoMode.TimeOut) {
> +      if (SerialPortPoll ()) {
> +        break;
> +      }
> +      gBS->Stall (10);
> +      TimeOut += 10;
> +    }
> +    if (TimeOut >= mSerialIoMode.TimeOut) {
> +      break;
> +    }
> +    SerialPortRead (Buffer, 1);
> +    Count++;
> +    Buffer = (VOID *) ((UINT8 *) Buffer + 1);
>    }
> 
>    if (Count != *BufferSize) {
> ====================
> 
> 
> Thanks,
> Star
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Heyi Guo
> Sent: Monday, July 17, 2017 12:23 PM
> To: edk2-devel@lists.01.org
> Subject: [edk2] MdeModulePkg/SerialDxe: Inconsistent timeout processing
> in SerialRead
> 
> Hi Folks,
> 
> In SerialRead function in MdeModulePkg/Universal/SerialDxe/SerialIo.c,
> it seems the timeout processing in SerialRead is not consistent.
> 
> Since SerialPortPoll only checks the status of serial port and returns
> immediately, and SerialPortRead does not really implement a time out
> mechanism and will always wait for enough input, it will cause below
> results:
> 
> 1. If there is no serial input at all, this interface will return timeout
> immediately without any waiting;
> 
> 2. If there is A characters in serial port FIFO, and caller requires A+1
> characters, it will wait until a new input is coming and timeout will not really
> occur.
> 
> As SerialPortLib is a simple library implementation, I think it is better to
> improve SerialIoDxe driver instead of SerialPortLib.
> 
> Please let me know your comments about this.
> 
> Thanks and regards,
> 
> Gary (Heyi Guo)
> 
> EFI_STATUS
> EFIAPI
> SerialRead (
>    IN EFI_SERIAL_IO_PROTOCOL *This,
>    IN OUT UINTN              *BufferSize,
>    OUT VOID                  *Buffer
>    )
> {
>    UINTN Count;
> 
>    Count = 0;
> 
>    if (SerialPortPoll ()) {
>      Count = SerialPortRead (Buffer, *BufferSize);
>    }
> 
>    if (Count != *BufferSize) {
>      *BufferSize = Count;
>      return EFI_TIMEOUT;
>    }
> 
>    return EFI_SUCCESS;
> }
> 
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