Re: [PATCH v6 2/3] MdePkg: add SBI-based SerialPortLib for RISC-V

["Sunil V L" <sunilvl@ventanamicro.com>]

Hi Andrei,

I had couple of questions on previous version of this patch. Adding them
inline again in case you had missed them. Please check if they are
valid.

Also, I think it would be better to have single directory
BaseSerialPortLibRiscVSbiLib and inside that we can have both INF files.
This way we can share UNI files etc between both libraries.

On Tue, Apr 04, 2023 at 11:43:58AM -0500, Andrei Warkentin wrote:
> These are implementations of SerialPortLib using SBI console services.
> - BaseSerialPortLibRiscVSbiLib is appropriate for SEC/PEI (XIP) environments
> - BaseSerialPortLibRiscVSbiLibRam is appropriate for PrePI/DXE environments
> 
> Tested with:
> - Qemu RiscVVirt (non-DBCN case, backed by UART)
> - TinyEMU + RiscVVirt (non-DBCN case, HTIF)
> - TinyEMU + RiscVVirt (DBCN case, HTIF)
> 
> Cc: Daniel Schaefer <git@danielschaefer.me>
> Cc: Sunil V L <sunilvl@ventanamicro.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Andrei Warkentin <andrei.warkentin@intel.com>
> ---
>  MdePkg/MdePkg.dsc                                                                  |   2 +
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf       |  39 +++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.inf |  36 +++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c         | 233 ++++++++++++++++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.c   | 288 ++++++++++++++++++++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.uni       |  16 ++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.uni |  16 ++
>  7 files changed, 630 insertions(+)
> 
> diff --git a/MdePkg/MdePkg.dsc b/MdePkg/MdePkg.dsc
> index 0ac7618b4623..ceccc078ff04 100644
> --- a/MdePkg/MdePkg.dsc
> +++ b/MdePkg/MdePkg.dsc
> @@ -192,5 +192,7 @@ [Components.ARM, Components.AARCH64]
>  
>  [Components.RISCV64]
>    MdePkg/Library/BaseRiscVSbiLib/BaseRiscVSbiLib.inf
> +  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> +  MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.inf
>  
>  [BuildOptions]
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> new file mode 100644
> index 000000000000..09cf59f190f6
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> @@ -0,0 +1,39 @@
> +## @file
> +#  Serial Port Library backed by SBI console.
> +#
> +#  Meant for SEC and PEI (XIP) environments.
> +#
> +#  Due to limitations of SBI console interface and XIP environments
> +#  (on use of globals), this library instance does not implement reading
> +#  and polling the serial port. See PrePiDxeSerialPortLibRiscVSbi for
> +#  the full-featured variant meant for PrePi and DXE environments.
> +#
> +#  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +#
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#
> +##
> +
> +[Defines]
> +  INF_VERSION                    = 0x0001001B
> +  BASE_NAME                      = BaseSerialPortLibRiscVSbiLib
> +  MODULE_UNI_FILE                = BaseSerialPortLibRiscVSbiLib.uni
> +  FILE_GUID                      = 639fad38-4bfd-4eb9-9f09-e97c7947d480
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = SerialPortLib | SEC PEI_CORE PEIM
> +
> +
> +#
> +#  VALID_ARCHITECTURES           = RISCV64
> +#
> +
> +[Sources]
> +  BaseSerialPortLibRiscVSbiLib.c
> +
> +[Packages]
> +  MdePkg/MdePkg.dec
> +
> +[LibraryClasses]
> +  RiscVSbiLib
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.inf b/MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.inf
> new file mode 100644
> index 000000000000..b7ad1548a309
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLibRam/BaseSerialPortLibRiscVSbiLibRam.inf
> @@ -0,0 +1,36 @@
> +## @file
> +#  Serial Port Library backed by SBI console.
> +#
> +#  Meant for PrePi and DXE environments (where globals are allowed). See
> +#  BaseSerialPortLibRiscVSbiLib for a reduced variant appropriate for SEC
> +#  and PEI (XIP) environments.
> +#
> +#  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +#
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#
> +##
> +
> +[Defines]
> +  INF_VERSION                    = 0x0001001B
> +  BASE_NAME                      = BaseSerialPortLibRiscVSbiLibRam
> +  MODULE_UNI_FILE                = BaseSerialPortLibRiscVSbiLibRam.uni
> +  FILE_GUID                      = 872af743-ab56-45b4-a065-602567f4820c
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = SerialPortLib | SEC DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_DRIVER UEFI_APPLICATION
> +
> +
> +#
> +#  VALID_ARCHITECTURES           = RISCV64
> +#
> +
> +[Sources]
> +  BaseSerialPortLibRiscVSbiLibRam.c
> +
> +[Packages]
> +  MdePkg/MdePkg.dec
> +
> +[LibraryClasses]
> +  RiscVSbiLib
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c
> new file mode 100644
> index 000000000000..0ad5931be3ae
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c
> @@ -0,0 +1,233 @@
> +/** @file
> +  Serial Port Library backed by SBI console.
> +
> +  Meant for SEC and PEI (XIP) environments.
> +
> +  Due to limitations of SBI console interface and XIP environments
> +  (on use of globals), this library instance does not implement reading
> +  and polling the serial port. See PrePiDxeSerialPortLibRiscVSbi for
> +  the full-featured variant meant for PrePi and DXE environments.
> +
> +  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#include <Base.h>
> +#include <Library/SerialPortLib.h>
> +#include <Library/BaseRiscVSbiLib.h>
> +
> +/**
> +  Initialize the serial device hardware.
> +
> +  If no initialization is required, then return RETURN_SUCCESS.
> +  If the serial device was successfully initialized, then return RETURN_SUCCESS.
> +  If the serial device could not be initialized, then return RETURN_DEVICE_ERROR.
> +
> +  @retval RETURN_SUCCESS        The serial device was initialized.
> +  @retval RETURN_DEVICE_ERROR   The serial device could not be initialized.
> +
> +**/
> +RETURN_STATUS
> +EFIAPI
> +SerialPortInitialize (
> +  VOID
> +  )
> +{
> +  return RETURN_SUCCESS;
> +}
> +
> +/**
> +  Write data from buffer to serial device.
> +
> +  Writes NumberOfBytes data bytes from Buffer to the serial device.
> +  The number of bytes actually written to the serial device is returned.
> +  If the return value is less than NumberOfBytes, then the write operation failed.
> +  If Buffer is NULL, then ASSERT().
> +  If NumberOfBytes is zero, then return 0.
> +
> +  @param  Buffer           The pointer to the data buffer to be written.
> +  @param  NumberOfBytes    The number of bytes to written to the serial device.
> +
> +  @retval 0                NumberOfBytes is 0.
> +  @retval >0               The number of bytes written to the serial device.
> +                           If this value is less than NumberOfBytes, then the write operation failed.
> +
> +**/
> +UINTN
> +EFIAPI
> +SerialPortWrite (
> +  IN UINT8  *Buffer,
> +  IN UINTN  NumberOfBytes
> +  )
> +{
> +  SBI_RET  Ret;
> +  UINTN    Index;
> +
> +  Ret = SbiCall (SBI_EXT_BASE, SBI_EXT_BASE_PROBE_EXT, 1, SBI_EXT_DBCN);
> +  if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +      (Ret.Value != 0))
> +  {
> +    Ret = SbiCall (
> +            SBI_EXT_DBCN,
> +            SBI_EXT_DBCN_WRITE,
> +            3,
> +            NumberOfBytes,
> +            ((UINTN)Buffer),
> +            0
> +            );
> +    if (TranslateError (Ret.Error) != EFI_SUCCESS) {
> +      return 0;
> +    }
> +
> +    return Ret.Value;
> +  }
> +
> +  Ret = SbiCall (SBI_EXT_BASE, SBI_EXT_BASE_PROBE_EXT, 1, SBI_EXT_0_1_CONSOLE_PUTCHAR);
> +  if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +      (Ret.Value != 0))
> +  {
> +    for (Index = 0; Index < NumberOfBytes; Index++) {
> +      SbiCall (SBI_EXT_0_1_CONSOLE_PUTCHAR, 0, 1, Buffer[Index]);
What happens if it fails? Shouldn't it return immediately instead of
continuing with the loop?

> +    }
> +
> +    return Index;
> +  }
> +
> +  /*
> +   * Neither DBCN or legacy extension were present.
> +   */
> +  return NumberOfBytes;
Isn't it an error? And for earlier DBCN_WRITE error, 0 is returned. So,
shouldn't we return 0 here also instead of NumberOfBytes?

Same questions for similar place in other library also.