Re: use of EFI_PCI_ATTRIBUTE_DUAL_ADDRESS_CYCLE

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Please ignore -- as Alan pointed out off list, I had
EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL and EFI_PCI_IO_PROTOCOL mixed up.


On 27 August 2016 at 17:37, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> The UEFI spec describes the EFI_PCI_ATTRIBUTE_DUAL_ADDRESS_CYCLE
> attribute as follows:
>
> """
> EFI_PCI_ATTRIBUTE_DUAL_ADDRESS_CYCLE
> This bit may only be used in the Attributes parameter to
> AllocateBuffer(). If this bit is set, then the PCI controller
> that is requesting a buffer through AllocateBuffer() 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 that is requesting a buffer through
> AllocateBuffer() is not capable of producing PCI Dual
> Address Cycles, so it is only able to access a 32-bit address space.
> """
>
> However, both the UEFI driver writer's guide, and the de facto use in
> Tianocore violate this, i.e., it use the pattern
>
> """
> //
> // Enable Command register and Dual Address Cycle
> //
> Status = PciIo->Attributes (
>     PciIo,
>     EfiPciIoAttributeOperationEnable,
>     (PciSupports & EFI_PCI_DEVICE_ENABLE) |
>     EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE,
>     NULL
>     );
> """
>
> to enable it in the PCI I/O layer, and the Map/Unmap implementations
> will switch to 64-bit flavors of the map operation, by the likes of
>
> """
>   if ((PciIoDevice->Attributes &
> EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE) != 0) {
>     Operation = (EFI_PCI_IO_PROTOCOL_OPERATION) (Operation +
> EfiPciOperationBusMasterRead64);
>   }
> """
>
> So what should we be doing in new code that needs to support 64-bit DMA?
>
> --
> Ard.