Re: [edk2-devel] [Question] How do you set PCIe host bridge address space granularity for a PCI host bridge defined with PciHostBridgeLib?

["Alexander D" <aenv067@gmail.com>]

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> 
> 1) when implementing PciHostBridgeLib, are we supposed to put host
> addresses (address the CPU uses after translation) in the Mem/MemAbove4G
> apertures or PCI/device addresses? (address the device uses before
> translation)

PCI_ROOT_BRIDGE_APERTURE is defined here: edk2/MdeModulePkg/Include/ Library/PciHostBridgeLib.h at master · tianocore/edk2 (github.com) ( https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Library/PciHostBridgeLib.h#L13 )

Base = Device Address
Translation = Device Address - Host Address.

Also worth noting that in an ACPI memory resource descriptor (DWordMemory, QWordMemory, ...), AddressTranslation (_TRA) is actually the opposite of above = Host Address - Device Address.

> 
> 2) Does the 'Mem' aperture have to be a 32 bit address/limit from host
> perspective?

From PCI device perspective. Host could have it mapped above 4 GB, and this is where you need translation.

> 
> 3) Does translation have to be 0 for Mem/MemAbove4G apertures in the
> PCI_ROOT_BRIDGE struct? Most example platforms do that, but I'm not sure
> if that's a requirement for PciHostBridgeLib or just convention.

It depends on how your platform maps PCI apertures in the CPU address space.
If an identity mapping is used (Host Address == Device Address) - ideally, then Translation is 0.


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