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Subject: Re: [edk2-devel] [PATCH edk2-platforms 2/2] Platform/Overdrive: enable BAR resizing
To: devel@edk2.groups.io, ard.biesheuvel@arm.com
Cc: leif@nuviainc.com
References: <20210114124615.8132-1-ard.biesheuvel@arm.com>
 <20210114124615.8132-2-ard.biesheuvel@arm.com>
From: "Laszlo Ersek" <lersek@redhat.com>
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Date: Thu, 14 Jan 2021 20:07:15 +0100
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On 01/14/21 13:46, Ard Biesheuvel wrote:
> Add support for BAR resizing at PCI resource allocation time: this removes
> the need for the OS to grow BARs of PCIe devices such as GPU controllers,
> which typically use small BARs by default for compatibility with 32-bit
> systems with small PCI resource windows, but perform better when the BAR
> can cover all of its onboard memory.
> 
> Usually, the OS should be capable of performing the BAR resize as well,
> but it is more constrained, and so doing this earlier is better on
> systems such as Overdrive where the MMIO root window is huge.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
>  Platform/AMD/OverdriveBoard/OverdriveBoard.dsc | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Platform/AMD/OverdriveBoard/OverdriveBoard.dsc b/Platform/AMD/OverdriveBoard/OverdriveBoard.dsc
> index adc92af080f1..17600a58112d 100644
> --- a/Platform/AMD/OverdriveBoard/OverdriveBoard.dsc
> +++ b/Platform/AMD/OverdriveBoard/OverdriveBoard.dsc
> @@ -404,6 +404,8 @@ [PcdsFixedAtBuild.common]
>    gArmTokenSpaceGuid.PcdPciMmio64Size|0x7F00000000
>    gArmTokenSpaceGuid.PcdPciMmio64Translation|0x0
>  
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdPcieResizableBarSupport|TRUE
> +
>    ## ACPI (no tables < 4GB)
>    gEfiMdeModulePkgTokenSpaceGuid.PcdAcpiExposedTableVersions|0x20
>  
> 

... this is exactly the kind of documentation that I wished for (in
retrospect) in the original edk2 feature addition.