On 11/27/17 13:20, Amit kumar wrote:
>
> Hi.
> I am trying to allocate a mem buffer above 4Gb address but the allocation
> since i am unable to locate EdkiiIoMmuProtocol.
>
> Status = gBS->LocateProtocol (, NULL, (VOID
> **));
> Status = mIoMmuProtocol->AllocateBuffer (
>mIoMmuProtocol,
>MaxAllocateType,
>EfiBootServicesData,
>1,
> HostAddress,
> EDKII_IOMMU_ATTRIBUTE_DUAL_ADDRESS_CYCLE
> );
PciHostBridgeDxe can perfectly well allocate >4GB memory for DMA
purposes even in the absence of the IOMMU protocol. For that, your PCI
device driver has to advertize the PCI device as 64-bit capable. In your
Driver Binding Start() function, call PciIo->Attributes() with the
EfiPciIoAttributeOperationEnable operation, and set
EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE. From the v2.7 UEFI spec (14.4
EFI PCI I/O Protocol):
If this bit is set, then the PCI controller is capable of producing
PCI Dual Address Cycles, so it is able to access a 64-bit address
space. If this bit is not set, then the PCI controller is not
capable of producing PCI Dual Address Cycles, so it is only able to
access a 32-bit address space.
PciHostBridgeDxe will ignore the bit if the root bridge that the device
belongs to is generally uncapable of 64-bit access. Please see
"DmaAbove4G" in the PciHostBridgeLib interface:
MdeModulePkg/Include/Library/PciHostBridgeLib.h
(You might notice that the PciHostBridgeDxe source code uses
EFI_PCI_ATTRIBUTE_DUAL_ADDRESS_CYCLE, but above I wrote
EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE. The PciBusDxe driver maps the
latter to the former, in the PciIoAllocateBuffer() function.)
Laszlo
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