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

["Yao, Jiewen" <jiewen.yao@intel.com>]

Good idea, Ard.

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

I like this suggestion.


Thank you
Yao Jiewen


> -----Original Message-----
> From: Ard Biesheuvel <ardb@kernel.org>
> Sent: Thursday, August 26, 2021 7:15 PM
> To: Gerd Hoffmann <kraxel@redhat.com>
> Cc: edk2-devel-groups-io <devel@edk2.groups.io>; Ard Biesheuvel
> <ardb+tianocore@kernel.org>; Yao, Jiewen <jiewen.yao@intel.com>; Justen,
> Jordan L <jordan.l.justen@intel.com>; Philippe Mathieu-Daude
> <philmd@redhat.com>
> Subject: Re: [PATCH v2 3/3] RFC: OvmfPkg/PlatformPei: stop using cmos for
> memory detection
> 
> 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
> >