Re: [PATCH v1 2/2] DynamicTablesPkg: Add an override for 16550 HID in SSDT

["Samer El-Haj-Mahmoud" <samer.el-haj-mahmoud@arm.com>]

> -----Original Message-----
> From: Joey Gouly <joey.gouly@arm.com>
> Sent: Wednesday, January 20, 2021 1:20 PM
> To: devel@edk2.groups.io
> Cc: Joey Gouly <Joey.Gouly@arm.com>; ardb+tianocore@kernel.org; Sami
> Mujawar <Sami.Mujawar@arm.com>; Jeff Brasen (jbrasen@nvidia.com)
> <jbrasen@nvidia.com>; ipark@nvidia.com; Samer El-Haj-Mahmoud
> <Samer.El-Haj-Mahmoud@arm.com>; nd <nd@arm.com>
> Subject: [PATCH v1 2/2] DynamicTablesPkg: Add an override for 16550 HID in
> SSDT
> 
> Some platforms advertise support for a 16550 UART, but are not compatible
> with the PNP0500 HID. Allow them to override the HID by setting
> PcdNonSbsaCompliantSerialHid.
> 
> Signed-off-by: Joey Gouly <joey.gouly@arm.com>
> ---
>  DynamicTablesPkg/DynamicTablesPkg.dec                                             |  3 +++
> 
> DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPortFix
> upLib.inf |  4 +++-
> 
> DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPortFix
> upLib.c   | 14 +++++++++++---
>  3 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/DynamicTablesPkg/DynamicTablesPkg.dec
> b/DynamicTablesPkg/DynamicTablesPkg.dec
> index
> 291a45a69679ae82219ecd2f26dfabfbab1f7f65..3ec4fff116a8f538be331edf34
> 1867948c025116 100644
> --- a/DynamicTablesPkg/DynamicTablesPkg.dec
> +++ b/DynamicTablesPkg/DynamicTablesPkg.dec
> @@ -44,5 +44,8 @@ [PcdsFixedAtBuild]
>    # Maximum number of Custom DT Generators
> 
> gEdkiiDynamicTablesPkgTokenSpaceGuid.PcdMaxCustomDTGenerators|1|UI
> NT16|0xC0000003
> 
> +  # Non SBSA Compliant Serial HID
> +
> +
> gEdkiiDynamicTablesPkgTokenSpaceGuid.PcdNonSbsaCompliantSerialHid|""|
> V
> + OID*|0x40000008
> +
>  [Guids]
>    gEdkiiDynamicTablesPkgTokenSpaceGuid = { 0xab226e66, 0x31d8, 0x4613, {
> 0x87, 0x9d, 0xd2, 0xfa, 0xb6, 0x10, 0x26, 0x3c } } diff --git
> a/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.inf
> b/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.inf
> index
> af3d404393f5f1385ab2d40f45f7222ab66f9b3a..b64825982e8fb7aaf78f3fd68
> 992e1c78d20c408 100644
> ---
> a/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.inf
> +++
> b/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialP
> +++ ortFixupLib.inf
> @@ -1,7 +1,7 @@
>  ## @file
>  #  SSDT Serial Port fixup Library
>  #
> -#  Copyright (c) 2020, Arm Limited. All rights reserved.<BR>
> +#  Copyright (c) 2020 - 2021, Arm Limited. All rights reserved.<BR>
>  #
>  #  SPDX-License-Identifier: BSD-2-Clause-Patent  ## @@ -28,3 +28,5 @@
> [LibraryClasses]
>    AmlLib
>    BaseLib
> 
> +[Pcd]
> +  gEdkiiDynamicTablesPkgTokenSpaceGuid.PcdNonSbsaCompliantSerialHid
> diff --git
> a/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.c
> b/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.c
> index
> 0ff071485ef25f4ca63de0eeab5120d1beece4db..73a8087ed8a8ff84b64531a3c
> 73d319585dfb6cf 100644
> ---
> a/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialPort
> FixupLib.c
> +++
> b/DynamicTablesPkg/Library/Common/SsdtSerialPortFixupLib/SsdtSerialP
> +++ ortFixupLib.c
> @@ -1,7 +1,7 @@
>  /** @file
>    SSDT Serial Port Fixup Library.
> 
> -  Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
> +  Copyright (c) 2019 - 2021, Arm Limited. All rights reserved.<BR>
> 
>    SPDX-License-Identifier: BSD-2-Clause-Patent
> 
> @@ -139,13 +139,21 @@ FixupIds (
>    AML_OBJECT_NODE_HANDLE    NameOpIdNode;
>    CONST CHAR8             * HidString;
>    CONST CHAR8             * CidString;
> +  CONST CHAR8             * NonSbsaHid;
> 
>    // Get the _CID and _HID value to write.
>    switch (SerialPortInfo->PortSubtype) {
>      case EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_FULL_16550:
>      {
> -      HidString = "PNP0501";
> -      CidString = "PNP0500";
> +      // If there is a non-SBSA compliant HID, use that.
> +      NonSbsaHid = (CONST CHAR8*)PcdGetPtr
> (PcdNonSbsaCompliantSerialHid);
> +      if ((NonSbsaHid != NULL) && (AsciiStrLen (NonSbsaHid) != 0)) {
> +        HidString = NonSbsaHid;
> +        CidString = "";
> +      } else {
> +        HidString = "PNP0501";
> +        CidString = "PNP0500";
> +      }
>        break;
>      }
>      case EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_ARM_PL011_UART:
> --

Since you are using PcdNonSbsaCompliantSerialHid to indicate that this is a non-BSA compliant 16550 UART, maybe rename the PCD to reflect that? The name PcdNonSbsaCompliantSerialHid may imply that this is not a PL011/ Arm SBSA Generic UART. BSA 1.0 allows both PL011/Generic UART (the definition moved from SBSA spec to the BSA spec)  OR a 16550 standard UART. In this case, we are saying the UART is a 16550-like UART, but not exactly standard (i.e. do not use the standard 16550 IDs)

Maybe PcdNon16550CompliantSerialHid or PcdNonBsa16550CompliantSerialHid  is a better name that matches what the code is doing?

The comments will need to change as well.