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

[Udit Kumar <udit.kumar@nxp.com>]

Hi Laszlo 

> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Tuesday, April 17, 2018 3:12 PM
> To: Udit Kumar <udit.kumar@nxp.com>; Leif Lindholm
> <leif.lindholm@linaro.org>
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; edk2-devel@lists.01.org;
> Gao, Liming <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] MdePkg: add big-endian MMIO BaseBeIoLib
> 
> On 04/17/18 10:15, Udit Kumar wrote:
> > Hi Laszlo,
> >
> > Considering all possible option is best to have in code 😊
> > But IMO, We are running UEFI on LE CPU only, Not sure someone is running on
> BE. AFAIK even specs says LE.
> >
> >> (c) assuming we introduce a CPU with BE byte order, the same driver
> >>     source will work (for both LE and BE devices), only the lib
> >>     instances will have to be switched around. (This might even happen
> >>     dynamically, via function pointers.)
> >
> > I assume , when we say CPU in BE , this means we are talking here new
> > CPU architecture and new SOC.  So I expect some changes in hardware IP as
> well.
> > If not then, I see still this working with patch of Leif
> >
> > Like
> > CPU (LE,) Driver (LE) Uses Mmio
> > CPU (LE,) Driver (BE) Uses BeMmio (Mmio with swap)
> >
> > CPU (BE,) Driver (LE) Uses Mmio (Does read and Swap) <-- This will be
> > new Mmio Lib for particular architecture CPU (BE,) Driver (BE) Uses
> > BeMmio (Mmio with swap)  <-- Swap of swap will make same value
> >
> > With this, I see driver code is same irrespective of CPU arch
> >
> > thoughts ?
> 
> Apparently I've needlessly complicated things already. Feel free to proceed as
> you see fit.

You haven't complicated the things , rather helping to get better solution !!
For me, patch from Leif, seems to work on BE or LE CPU. 
With as it is patch, Apart from edk2 coding rules, one limitation  I see for BE CPU having BE IP device driver, swap will be done twice.

On lighter note, 
To keep things simple, I need to request hardware designer to stay away from BE IP in next SOC 😊 

> Laszlo