Re: [PATCH v2 3/3] RFC: OvmfPkg/PlatformPei: stop using cmos for memory detection

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 26 Aug 2021 at 11:55, Gerd Hoffmann <kraxel@redhat.com> wrote:
>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3593
>
> Not needed for qemu 1.7 (released in 2013) and newer.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  OvmfPkg/PlatformPei/MemDetect.c | 58 ++-------------------------------
>  1 file changed, 3 insertions(+), 55 deletions(-)
>
> diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
> index 20154255324b..8d2c7f432472 100644
> --- a/OvmfPkg/PlatformPei/MemDetect.c
> +++ b/OvmfPkg/PlatformPei/MemDetect.c
> @@ -37,7 +37,6 @@ Module Name:
>  #include <Library/QemuFwCfgSimpleParserLib.h>
>
>  #include "Platform.h"
> -#include "Cmos.h"
>
>  UINT8 mPhysMemAddressWidth;
>
> @@ -295,52 +294,11 @@ GetSystemMemorySizeBelow4gb (
>  {
>    EFI_STATUS Status;
>    UINT64 LowerMemorySize = 0;
> -  UINT8 Cmos0x34;
> -  UINT8 Cmos0x35;
>
>    Status = ScanOrAdd64BitE820Ram (FALSE, &LowerMemorySize, NULL);
> -  if (Status == EFI_SUCCESS && LowerMemorySize > 0) {
> -    return LowerMemorySize;
> -  }
> +  ASSERT (Status == EFI_SUCCESS && LowerMemorySize > 0);

Nit: better to do

ASSERT_EFI_ERROR (Status);
ASSERT (LowerMemorySize > 0);

so that you can tell from the debug log which condition triggered, and
if it is the first one, what the actual error code was.


> +  return LowerMemorySize;
>
> -  //
> -  // CMOS 0x34/0x35 specifies the system memory above 16 MB.
> -  // * CMOS(0x35) is the high byte
> -  // * CMOS(0x34) is the low byte
> -  // * The size is specified in 64kb chunks
> -  // * Since this is memory above 16MB, the 16MB must be added
> -  //   into the calculation to get the total memory size.
> -  //
> -
> -  Cmos0x34 = (UINT8) CmosRead8 (0x34);
> -  Cmos0x35 = (UINT8) CmosRead8 (0x35);
> -
> -  return (UINT32) (((UINTN)((Cmos0x35 << 8) + Cmos0x34) << 16) + SIZE_16MB);
> -}
> -
> -
> -STATIC
> -UINT64
> -GetSystemMemorySizeAbove4gb (
> -  )
> -{
> -  UINT32 Size;
> -  UINTN  CmosIndex;
> -
> -  //
> -  // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
> -  // * CMOS(0x5d) is the most significant size byte
> -  // * CMOS(0x5c) is the middle size byte
> -  // * CMOS(0x5b) is the least significant size byte
> -  // * The size is specified in 64kb chunks
> -  //
> -
> -  Size = 0;
> -  for (CmosIndex = 0x5d; CmosIndex >= 0x5b; CmosIndex--) {
> -    Size = (UINT32) (Size << 8) + (UINT32) CmosRead8 (CmosIndex);
> -  }
> -
> -  return LShiftU64 (Size, 16);
>  }
>
>
> @@ -371,12 +329,9 @@ GetFirstNonAddress (
>    // If QEMU presents an E820 map, then get the highest exclusive >=4GB RAM
>    // address from it. This can express an address >= 4GB+1TB.
>    //
> -  // Otherwise, get the flat size of the memory above 4GB from the CMOS (which
> -  // can only express a size smaller than 1TB), and add it to 4GB.
> -  //
>    Status = ScanOrAdd64BitE820Ram (FALSE, NULL, &FirstNonAddress);
>    if (EFI_ERROR (Status)) {
> -    FirstNonAddress = BASE_4GB + GetSystemMemorySizeAbove4gb ();
> +    FirstNonAddress = BASE_4GB;
>    }
>
>    //
> @@ -719,7 +674,6 @@ QemuInitializeRam (
>    )
>  {
>    UINT64                      LowerMemorySize;
> -  UINT64                      UpperMemorySize;
>    MTRR_SETTINGS               MtrrSettings;
>    EFI_STATUS                  Status;
>
> @@ -775,12 +729,6 @@ QemuInitializeRam (
>      // memory size read from the CMOS.
>      //
>      Status = ScanOrAdd64BitE820Ram (TRUE, NULL, NULL);
> -    if (EFI_ERROR (Status)) {
> -      UpperMemorySize = GetSystemMemorySizeAbove4gb ();
> -      if (UpperMemorySize != 0) {
> -        AddMemoryBaseSizeHob (BASE_4GB, UpperMemorySize);
> -      }
> -    }
>    }
>
>    //
> --
> 2.31.1
>