Re: [PATCH] MdePkg: add big-endian MMIO BaseBeIoLib

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Leif,

Yes.  I think the single swap lib is sufficient for
the specific use case.

We can wait until there is a request to add support 
for a BE CPU to look at a more complete solution to
reusing the same module sources for all combinations
of CPU and I/O endianness.

Thanks,

Mike

> -----Original Message-----
> From: Leif Lindholm [mailto:leif.lindholm@linaro.org]
> Sent: Tuesday, April 17, 2018 6:27 AM
> To: Kinney, Michael D <michael.d.kinney@intel.com>;
> Gao, Liming <liming.gao@intel.com>; Laszlo Ersek
> <lersek@redhat.com>
> Cc: edk2-devel@lists.01.org
> Subject: Re: [edk2] [PATCH] MdePkg: add big-endian MMIO
> BaseBeIoLib
> 
> On Mon, Apr 16, 2018 at 10:42:26PM +0200, Laszlo Ersek
> wrote:
> > On 04/16/18 16:34, Michael Brown wrote:
> > > On 16/04/18 15:10, Kinney, Michael D wrote:
> > >> I agree that the opposite use case is a BE CPU
> > >> needing a LE operation.
> > >>
> > >> I think we only need a single lib class and lib
> > >> Instance that does the byte swap and we should
> > >> not use Le or Be in any of the names of the class,
> > >> instance, or APIs.  Just "Swap".
> > >
> > > I may have misunderstood, but wouldn't using "Swap"
> within the API names
> > > effectively encode knowledge of the endianness of
> the _build_ platform
> > > into the source code?  This would prevent the same
> source code being
> > > built for both little-endian and big-endian CPUs.
> >
> > Under this scenario, all drivers meant to be portable
> to both byte
> > orders would have to:
> > - link against both IoLib and IoSwapLib,
> > - determine at device binding time, from CPU
> endianness and device
> >   endianness combined, whether swapping was needed
> for that device,
> > - call the IoLib or IoSwapLib APIs through wrapper
> functions, or
> >   function pointers.
> 
> Yes. I'm thinking that is a good enough solution for
> this type of
> situation and I overcomplicated things. Apologies for
> that.
> 
> We are talking about the relatively unusual situation
> where an
> otherwise driver-compatible device can in some
> platforms be of a
> different endianness than in others.
> 
> So, Mike, Liming - would you be OK with a solution
> similar to
> https://www.mail-archive.com/edk2-
> devel@lists.01.org/msg36520.html.
> 
> /
>     Leif