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

[Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>]

Hi All,


It’s a pretty old discussion, we have left the upstreaming of NXP package in between because of some other work, but have started it again now.


Issue  : Few NXP modules support Big Endian MMIOs as these are ported from PowerPC.

Solution suggested : Create a separate library for BE MMIO APIs.


So what I have done is, I have created a separate library to support BE MMIO APIs and currently keeping it to my package.
This library is basically a wrapper over existing MMIO APIs.

UINT32
EFIAPI
BeMmioRead32 (
  IN  UINTN     Address
  )
{
  UINT32  Value;

  Value = MmioRead32(Address);

  return SwapBytes32(Value);
}


Need your opinion on below optinos:

1. Will this be a good idea to make this library a part of MdePkg? OR

2. Add a new file e.g. IoBeMmio.c like IoHighLevel.c in MdePkg/Library/BaseIoLibIntrinsic/
 And made these APIs a part of IoLib itself. OR

3. Keep this library internal to NXP package.


Please provide your inputs.


Thanks & Regards,
Meenakshi

> -----Original Message-----
> From: Bhupesh Sharma
> Sent: Monday, October 17, 2016 3:28 PM
> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>; Kinney, Michael D
> <michael.d.kinney@intel.com>
> Cc: Gao, Liming <liming.gao@intel.com>; edk2-devel@ml01.01.org;
> Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
> Subject: RE: [edk2] [PATCH 1/1] MdePkg/IoLib: Add support for big-endian
> MMIO
> 
> Hi Ard,
> 
> > -----Original Message-----
> > From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
> > Sent: Monday, October 17, 2016 1:12 PM
> > To: Kinney, Michael D <michael.d.kinney@intel.com>
> > Cc: Gao, Liming <liming.gao@intel.com>; Bhupesh Sharma
> > <bhupesh.sharma@nxp.com>; edk2-devel@ml01.01.org
> > Subject: Re: [edk2] [PATCH 1/1] MdePkg/IoLib: Add support for big-
> > endian MMIO
> >
> > 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
> > }
> 
> That's correct. I think creating a separate IoLib for byte-swapping makes
> sense.
> 
> We will rework the patch accordingly.
> 
> Regards,
> Bhupesh