Re: [edk2-platforms PATCH v3 1/3] SbsaQemu: Add FdtHelperLib

["Leif Lindholm" <leif@nuviainc.com>]

On Thu, Feb 18, 2021 at 20:57:39 -0700, Rebecca Cran wrote:
> The CountCpusFromFdt function is now used in two places. Create
> FdtHelperLib for this and similar functions.
> 
> Signed-off-by: Rebecca Cran <rebecca@nuviainc.com>

Reviewed-by: Leif Lindholm <leif@nuviainc.com>
One comment below, you can fold in or not and still keep the reviewed-by.

> ---
>  Platform/Qemu/SbsaQemu/SbsaQemu.dsc                         |  2 +
>  Silicon/Qemu/SbsaQemu/Include/Library/FdtHelperLib.h        | 24 +++++++
>  Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.c   | 69 ++++++++++++++++++++
>  Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.inf | 28 ++++++++
>  4 files changed, 123 insertions(+)
> 
> diff --git a/Platform/Qemu/SbsaQemu/SbsaQemu.dsc b/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
> index f6af3f9111ee..8faad3eda217 100644
> --- a/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
> +++ b/Platform/Qemu/SbsaQemu/SbsaQemu.dsc
> @@ -121,6 +121,8 @@ DEFINE NETWORK_HTTP_BOOT_ENABLE       = FALSE
>    # ARM PL011 UART Driver
>    PL011UartLib|ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.inf
>  
> +  FdtHelperLib|Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.inf
> +
>    # Debug Support
>    PeCoffExtraActionLib|ArmPkg/Library/DebugPeCoffExtraActionLib/DebugPeCoffExtraActionLib.inf
>    DebugAgentLib|MdeModulePkg/Library/DebugAgentLibNull/DebugAgentLibNull.inf
> diff --git a/Silicon/Qemu/SbsaQemu/Include/Library/FdtHelperLib.h b/Silicon/Qemu/SbsaQemu/Include/Library/FdtHelperLib.h
> new file mode 100644
> index 000000000000..eac47349a3d7
> --- /dev/null
> +++ b/Silicon/Qemu/SbsaQemu/Include/Library/FdtHelperLib.h
> @@ -0,0 +1,24 @@
> +/** @file
> +*  FdtHelperLib.h
> +*
> +*  Copyright (c) 2021, NUVIA Inc. All rights reserved.
> +*
> +*  SPDX-License-Identifier: BSD-2-Clause-Patent
> +*
> +**/
> +
> +#ifndef FDT_HELPER_LIB_
> +#define FDT_HELPER_LIB_
> +
> +/** Walks through the Device Tree created by Qemu and counts the number
> +    of CPUs present in it.
> +
> +    @return The number of CPUs present.
> +**/
> +EFIAPI
> +UINT16

There is no inherent need to restrict this function to a 16-bit return
value (and on RISC architectures, this generally means extra masking
going on).
Indeed, the implementation uses a 32-bit value, then returns the
bottom 16 bits of that.
I guess this ends up going into a 16-bit field somewhere else?
Another way to deal with that would be to take the full 32-bit value
and ASSERT at the point of stuffing the table.

/
    Leif

> +CountCpusFromFdt (
> +  VOID
> +  );
> +
> +#endif /* FDT_HELPER_LIB_ */
> diff --git a/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.c b/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.c
> new file mode 100644
> index 000000000000..c399fec5f9c7
> --- /dev/null
> +++ b/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.c
> @@ -0,0 +1,69 @@
> +/** @file
> +*  FdtHelperLib.c
> +*
> +*  Copyright (c) 2021, NUVIA Inc. All rights reserved.
> +*  Copyright (c) 2020, Linaro Ltd. All rights reserved.
> +*
> +*  SPDX-License-Identifier: BSD-2-Clause-Patent
> +*
> +**/
> +
> +
> +/** Walks through the Device Tree created by Qemu and counts the number
> +    of CPUs present in it.
> +
> +    @return The number of CPUs present.
> +**/
> +
> +#include <Uefi.h>
> +#include <Library/DebugLib.h>
> +#include <Library/FdtHelperLib.h>
> +#include <Library/PcdLib.h>
> +#include <libfdt.h>
> +
> +/** Walks through the Device Tree created by Qemu and counts the number
> +    of CPUs present in it.
> +
> +    @return The number of CPUs present.
> +**/
> +EFIAPI
> +UINT16
> +CountCpusFromFdt (
> +  VOID
> +  )
> +{
> +  VOID   *DeviceTreeBase;
> +  INT32  Node;
> +  INT32  Prev;
> +  INT32  CpuNode;
> +  INT32  CpuCount;
> +
> +  DeviceTreeBase = (VOID *)(UINTN)PcdGet64 (PcdDeviceTreeBaseAddress);
> +  ASSERT (DeviceTreeBase != NULL);
> +
> +  // Make sure we have a valid device tree blob
> +  ASSERT (fdt_check_header (DeviceTreeBase) == 0);
> +
> +  CpuNode = fdt_path_offset (DeviceTreeBase, "/cpus");
> +  if (CpuNode <= 0) {
> +    DEBUG ((DEBUG_ERROR, "Unable to locate /cpus in device tree\n"));
> +    return 0;
> +  }
> +
> +  CpuCount = 0;
> +
> +  // Walk through /cpus node and count the number of subnodes.
> +  // The count of these subnodes corresponds to the number of
> +  // CPUs created by Qemu.
> +  Prev = fdt_first_subnode (DeviceTreeBase, CpuNode);
> +  while (1) {
> +    CpuCount++;
> +    Node = fdt_next_subnode (DeviceTreeBase, Prev);
> +    if (Node < 0) {
> +      break;
> +    }
> +    Prev = Node;
> +  }
> +
> +  return CpuCount;
> +}
> diff --git a/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.inf b/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.inf
> new file mode 100644
> index 000000000000..d84c16f888d1
> --- /dev/null
> +++ b/Silicon/Qemu/SbsaQemu/Library/FdtHelperLib/FdtHelperLib.inf
> @@ -0,0 +1,28 @@
> +#/** @file
> +#
> +#  Component description file for FdtHelperLib module
> +#
> +#  Copyright (c) 2021, NUVIA Inc. All rights reserved.
> +#
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#**/
> +
> +[Defines]
> +  INF_VERSION                    = 1.29
> +  BASE_NAME                      = FdtHelperLib
> +  FILE_GUID                      = 34e4396f-c2fc-4f9e-ad58-0f98e99e3875
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = FdtHelperLib
> +
> +[Sources.common]
> +  FdtHelperLib.c
> +
> +[Packages]
> +  EmbeddedPkg/EmbeddedPkg.dec
> +  MdePkg/MdePkg.dec
> +  Silicon/Qemu/SbsaQemu/SbsaQemu.dec
> +
> +[FixedPcd]
> +  gArmVirtSbsaQemuPlatformTokenSpaceGuid.PcdDeviceTreeBaseAddress
> -- 
> 2.26.2
>