Re: [edk2-devel] [PATCH edk2-platforms v1 1/1] Platform/ARM: Reduce System Memory Size for FVP with RME extensions

["Leif Lindholm" <quic_llindhol@quicinc.com>]

Hi Sami,

On Mon, Apr 17, 2023 at 14:22:49 +0100, Sami Mujawar wrote:
> For older FVPs (without support for RME extension) the top 16MB of
> DRAM1 is reserved as Trusted DRAM. However, the latest FVP Base RevC
> AEM Model [1] has support for RME extension. When RME extension is
> present the top 64MB of DRAM1 (i.e. at the top of the 32bit address
> space) is carved out for four-world support in TF-A [2].
> 
> Therefore, reduce the System Memory size by 64MB.

This is clearly needed in order to not break things, so
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
*but*
this is really just extending the life of a horrible hack.

Ideally, the ARM ltd. platforms should lead the way in providing
reference implementations - since inevitably people will look to those
for creating new platform ports. Things like this should be runtime
discoverable.

/
    Leif

> Reference:
> [1] FVP Base RevC AEM Model (available on x86_64 / Arm64 Linux)
> (https://developer.arm.com/Tools%20and%20Software/
> Fixed%20Virtual%20Platforms)
> 
> [2] commit c872072 (https://review.trustedfirmware.org/plugins/gitiles/
> TF-A/trusted-firmware-a/+/c8720729726faffc39ec64f3a02440a48c8c305a))
> 
> Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
> ---
>  Platform/ARM/VExpressPkg/ArmVExpress-FVP-AArch64.dsc | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/Platform/ARM/VExpressPkg/ArmVExpress-FVP-AArch64.dsc b/Platform/ARM/VExpressPkg/ArmVExpress-FVP-AArch64.dsc
> index dc081794cf98a27c667ef85bd27dacd80e9e8bd2..f70a4d52ba06f570e017ab5286f06d87193753e5 100644
> --- a/Platform/ARM/VExpressPkg/ArmVExpress-FVP-AArch64.dsc
> +++ b/Platform/ARM/VExpressPkg/ArmVExpress-FVP-AArch64.dsc
> @@ -107,9 +107,12 @@ [PcdsFixedAtBuild.common]
>    gArmPlatformTokenSpaceGuid.PcdCPUCorePrimaryStackSize|0x4000
>    gArmPlatformTokenSpaceGuid.PcdCPUCoreSecondaryStackSize|0x0
>  
> -  # System Memory (2GB - 16MB of Trusted DRAM at the top of the 32bit address space)
> +  # System Memory
> +  # When RME is supported by the FVP the top 64MB of DRAM1 (i.e. at the top
> +  # of the 32bit address space) is reserved for four-world support in TF-A.
> +  # Therefore, set the default System Memory size to (2GB - 64MB).
>    gArmTokenSpaceGuid.PcdSystemMemoryBase|0x80000000
> -  gArmTokenSpaceGuid.PcdSystemMemorySize|0x7F000000
> +  gArmTokenSpaceGuid.PcdSystemMemorySize|0x7C000000
>  
>    # Size of the region used by UEFI in permanent memory (Reserved 64MB)
>    gArmPlatformTokenSpaceGuid.PcdSystemMemoryUefiRegionSize|0x04000000
> -- 
> 'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'
> 
> 
> 
> 
> 
>