Re: [PATCH 1/1] MdePkg/IoLib: Add support for big-endian MMIO

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

On 17 October 2016 at 05:10, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
> Bhupesh,
>
> It is also possible to add an ARM specific PCD to select endianness and update
> MdePkg/Library/BaseIoLibIntrinsic/IoLibArm.c to use that PCD in MmioRead/Write()
> APIs in that file to support both endian types.  You can use the SwapBytesxx()
> functions from BaseLib(as Laszlo suggested) based on the setting of this ARM
> specific PCD.
>
> Modules that link against this lib can select endianness by setting PCD in the
> scope of that module.
>
> The IPF version of IoLib uses an IPF specific PCD to translate I/O port accesses
> to MMIO accesses.  So there is already an example of an arch specific PCD in this
> lib instance.
>

This is not a platform wide thing, it is a per-device property whether
the MMIO occurs in big endian or little endian manner.

So I think Liming's suggestion makes sense: create an IoLib
implementation that performs the byte swapping, and selectively
incorporate it into drivers that require it using

BeMmioDeviceDxe.inf {
  <LibraryClasses>
    IoLib|SomePkg/Library/BigEndianIoLib.inf
}