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

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

Hi Leif,


Michael is in favor of adding separate APIs for byte swap operation and 
We also prefer keeping it as a separate library because of following use case:

Driver which is in BE mode, and is using DebugLib which uses SerialPortLib, which is in LE mode.
This is the main issue because of which we cannot use same APIs for byte swapping.


Please give your views.


Thanks,
Meenakshi

> -----Original Message-----
> From: Kinney, Michael D [mailto:michael.d.kinney@intel.com]
> Sent: Saturday, December 02, 2017 4:11 AM
> To: Udit Kumar <udit.kumar@nxp.com>; Leif Lindholm
> <leif.lindholm@linaro.org>; Meenakshi Aggarwal
> <meenakshi.aggarwal@nxp.com>; Varun Sethi <V.Sethi@nxp.com>; Kinney,
> Michael D <michael.d.kinney@intel.com>
> Cc: edk2-devel@lists.01.org; Gao, Liming <liming.gao@intel.com>; Ard
> Biesheuvel <ard.biesheuvel@linaro.org>
> Subject: RE: [edk2] [PATCH 1/1] MdePkg/IoLib: Add support for big-endian
> MMIO
> 
> Udit,
> 
> I agree with your concern.
> 
> I am in favor of adding new APIs that perform the
> byte swap operations.
> 
> Mike
> 
> > -----Original Message-----
> > From: Udit Kumar [mailto:udit.kumar@nxp.com]
> > Sent: Friday, December 1, 2017 9:58 AM
> > To: Leif Lindholm <leif.lindholm@linaro.org>; Meenakshi
> > Aggarwal <meenakshi.aggarwal@nxp.com>; Varun Sethi
> > <V.Sethi@nxp.com>
> > Cc: Kinney, Michael D <michael.d.kinney@intel.com>; edk2-
> > devel@lists.01.org; Gao, Liming <liming.gao@intel.com>;
> > Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Subject: RE: [edk2] [PATCH 1/1] MdePkg/IoLib: Add support
> > for big-endian MMIO
> >
> > Thanks Leif,
> >
> > > It may require a little bit more of up-front work, but
> > the end result will be a
> > > platform port that works with the intended edk2 design
> > principles rather than
> >
> > Yes, this will be re-design/code for us, breaking all
> > software pieces into
> > smaller blocks and exposing protocol from the same.
> > This could be managed.
> >
> > But how do you see,  if there is such dependency oN lib.
> > Say a driver which is in BE mode, and is using DebugLib
> > (BaseDebugLibSerialPort)
> > And DebugLib uses SerialPortLib, which is in LE mode
> >
> > Thanks
> > Udit
> >
> > > -----Original Message-----
> > > From: edk2-devel [mailto:edk2-devel-
> > bounces@lists.01.org] On Behalf Of Leif
> > > Lindholm
> > > Sent: Friday, December 01, 2017 4:28 PM
> > > To: Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
> > > Cc: Kinney, Michael D <michael.d.kinney@intel.com>;
> > edk2-devel@lists.01.org;
> > > Gao, Liming <liming.gao@intel.com>; Ard Biesheuvel
> > > <ard.biesheuvel@linaro.org>
> > > Subject: Re: [edk2] [PATCH 1/1] MdePkg/IoLib: Add
> > support for big-endian
> > > MMIO
> > >
> > > On Thu, Nov 30, 2017 at 04:15:38AM +0000, Meenakshi
> > Aggarwal wrote:
> > > > Hi Leif, Mike,
> > > >
> > > >
> > > > NXP boards, at present, have few controllers with big
> > endian and other
> > > > with little endian memory access.
> > >
> > > Sure, this is not a problem.
> > >
> > > > Maximum controllers depend on SocLib library for
> > clock information and
> > > > endianness for SocLib and controllers is different.
> > >
> > > OK, I see in SocLib you have something called a Gur
> > that is read once (and again
> > > does a special per-device Pcd dance for runtime
> > selection between
> > > byteswapping Mmio and plain Mmio).
> > >
> > > > So this option will not work for us,
> > > >   You would then just do (in your .dsc):
> > > >   Platform/NXP/Drivers/WatchDog/WatchDogDxe.inf {
> > > >       IoLib|<path to BeIoLib .inf>
> > > >   }
> > > >
> > > > Because all libraries included by WatchDog will then
> > access BE mode Mmio
> > > APIs.
> > >
> > > Which libraries performing Mmio accesses are you
> > intending to include in your
> > > watchdog driver? You have submitted none as part of
> > this series.
> > >
> > > > And breaking code into separate modules with
> > different access will be
> > > > very difficult.
> > >
> > > It may require a little bit more of up-front work, but
> > the end result will be a
> > > platform port that works with the intended edk2 design
> > principles rather than
> > > against them. And that will reduce the overall effort
> > (not to mention code
> > > duplication).
> > >
> > > From the patches you have sent, the only required
> > change I see (if a
> > > byteswapping IoLib was added to edk2) would be to
> > create a tiny driver for this
> > > "Gur" device that installs a protocol containing a
> > single function for reading
> > > from that device's register space. That driver can be
> > built against the swapping
> > > or non-swapping IoLib as appropriate.
> > >
> > > > Watchdog is not the only module which need BE Mmio
> > APIs, we have MMC
> > > > and other controllers also with same requirement.
> > >
> > > And the same solutions are possible everywhere.
> > >
> > > Best Regards,
> > >
> > > Leif
> > >
> > > > We need BE Mmio APIs with a different name.
> > > >
> > > > Please see the possibility.
> > > >
> > > > Thanks & Regards,
> > > > Meenakshi
> > > >
> > > > > -----Original Message-----
> > > > > From: Leif Lindholm
> > [mailto:leif.lindholm@linaro.org]
> > > > > Sent: Thursday, November 30, 2017 1:19 AM
> > > > > To: Kinney, Michael D <michael.d.kinney@intel.com>
> > > > > Cc: Meenakshi Aggarwal
> > <meenakshi.aggarwal@nxp.com>; Gao, Liming
> > > > > <liming.gao@intel.com>; edk2-devel@lists.01.org;
> > Ard Biesheuvel
> > > > > <ard.biesheuvel@linaro.org>
> > > > > Subject: Re: [edk2] [PATCH 1/1] MdePkg/IoLib: Add
> > support for
> > > > > big-endian MMIO
> > > > >
> > > > > I guess there is no strict rule about a driver only
> > directly
> > > > > accessing one piece of HW?
> > > > >
> > > > > Still, that would be one possible solution:
> > breaking accesses to a
> > > > > separate HW in need of byteswapping out into its
> > own module and
> > > > > letting it override IoLib version there.
> > > > >
> > > > > Regards,
> > > > >
> > > > > Leif
> > > > >
> > > > > On Wed, Nov 29, 2017 at 07:25:05PM +0000, Kinney,
> > Michael D wrote:
> > > > > > Leif,
> > > > > >
> > > > > > I agree that this should be described as byte
> > swapping.
> > > > > >
> > > > > > What about a module that needs to access HW with
> > and without the
> > > > > > bytes swapped?  It gets more complex if a module
> > is linked against
> > > > > > several libs and some libs access HW with bytes
> > swapped and some
> > > > > > do not.
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Mike
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: edk2-devel [mailto:edk2-devel-
> > bounces@lists.01.org] On
> > > > > > > Behalf Of Leif Lindholm
> > > > > > > Sent: Wednesday, November 29, 2017 4:51 AM
> > > > > > > To: Meenakshi Aggarwal
> > <meenakshi.aggarwal@nxp.com>; Gao, Liming
> > > > > > > <liming.gao@intel.com>
> > > > > > > Cc: Kinney, Michael D
> > <michael.d.kinney@intel.com>;
> > > > > > > edk2-devel@lists.01.org; Ard Biesheuvel
> > > > > > > <ard.biesheuvel@linaro.org>
> > > > > > > Subject: Re: [edk2] [PATCH 1/1] MdePkg/IoLib:
> > Add support for
> > > > > > > big-endian MMIO
> > > > > > >
> > > > > > > Hi Meenakshi,
> > > > > > >
> > > > > > > I finally got around to looking at the watchdog
> > code (that uses
> > > > > > > this library), and that has convinced me the
> > best solution is to
> > > > > > > do what Liming proposed.
> > > > > > >
> > > > > > > Looking at this snippet:
> > > > > > >
> > > > > > > > +STATIC
> > > > > > > > +UINT16
> > > > > > > > +EFIAPI
> > > > > > > > +WdogRead (
> > > > > > > > +  IN  UINTN     Address
> > > > > > > > +  )
> > > > > > > > +{
> > > > > > > > +  if (FixedPcdGetBool (PcdWdogBigEndian)) {
> > > > > > > > +    return BeMmioRead16 (Address);
> > > > > > > > +  } else {
> > > > > > > > +    return MmioRead16(Address);
> > > > > > > > +  }
> > > > > > >
> > > > > > > This is actually a pretty good demonstration of
> > the arguments
> > > > > > > that were made with regards to how the BeIoLib
> > could be just
> > > > > > > another implementation of IoLib.
> > > > > > >
> > > > > > > You would then just do (in your .dsc):
> > > > > > >   Platform/NXP/Drivers/WatchDog/WatchDogDxe.inf
> > {
> > > > > > >     IoLib|<path to BeIoLib .inf>
> > > > > > >   }
> > > > > > >
> > > > > > > This causes the big-endian version of the
> > library to be used for
> > > > > > > this component. This makes these Wdog<access>
> > functions and the
> > > > > > > Pcd redundant, and the rest of the code can use
> > > > > > > MmioRead16()/MmioWrite16()
> > > > > > > directly.
> > > > > > >
> > > > > > > But then, it is not really a big-endian or
> > litte-endian version
> > > > > > > of the library we need. We always know which
> > endianness we are
> > > > > > > building for.
> > > > > > > What we need is a byteswapping flavour of
> > IoLib.
> > > > > > >
> > > > > > > So Liming, what if we do something like adding
> > a
> > > > > > >
> > MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsicSwa
> > > > > > > p.inf
> > > > > > > ---
> > > > > > > [Defines]
> > > > > > >   INF_VERSION                    = 0x0001001A
> > > > > > >   BASE_NAME                      =
> > > > > > > BaseIoLibIntrinsicSwap
> > > > > > >   MODULE_UNI_FILE                =
> > > > > > > BaseIoLibIntrinsic.uni
> > > > > > >   FILE_GUID                      = d4a60d44-
> > 3688-4a50-
> > > > > > > b2d0-5c6fc2422523
> > > > > > >   MODULE_TYPE                    = BASE
> > > > > > >   VERSION_STRING                 = 1.0
> > > > > > >   LIBRARY_CLASS                  = IoLib
> > > > > > >
> > > > > > >
> > > > > > > #
> > > > > > > #  VALID_ARCHITECTURES           = IA32 X64 EBC
> > IPF ARM
> > > > > > > AARCH64
> > > > > > > #
> > > > > > >
> > > > > > > [Sources]
> > > > > > >   BaseIoLibIntrinsicInternal.h
> > > > > > >   IoHighLevel.c
> > > > > > >   IoLib.c
> > > > > > >   IoLibEbc.c         # Asserts on all i/o port
> > accesses
> > > > > > >   IoLibMmioBuffer.c
> > > > > > >
> > > > > > > [Packages]
> > > > > > >   MdePkg/MdePkg.dec
> > > > > > >
> > > > > > > [LibraryClasses]
> > > > > > >   DebugLib
> > > > > > >   BaseLib
> > > > > > >
> > > > > > > [BuildOptions]
> > > > > > >   GCC:*_*_*_CC_FLAGS  = -DSWAP_BYTES
> > > > > > > ---
> > > > > > >
> > > > > > > And then add
> > > > > > >
> > > > > > > #ifdef SWAP_BYTES
> > > > > > >   return SwapBytesXX (Value);
> > > > > > > #else
> > > > > > >   return Value;
> > > > > > > #fi
> > > > > > >
> > > > > > > for the read operations and
> > > > > > >
> > > > > > > #ifdef SWAP_BYTES
> > > > > > >   *(type)Address = SwapBytesXX (Value); #else
> > > > > > >   *(type)Address = Value;
> > > > > > > #fi
> > > > > > >
> > > > > > > for the write operations in IoLib.c?
> > > > > > >
> > > > > > > /
> > > > > > >     Leif
> > > > > > >
> > > > > > > On Mon, Nov 27, 2017 at 06:06:33AM +0000,
> > Meenakshi Aggarwal
> > > > > > > wrote:
> > > > > > > > Hi Leif,
> > > > > > > >
> > > > > > > > This is regarding Big-Endian Library patch
> > ([PATCH v2
> > > > > > > 1/9]
> > > > > > > > Platform/NXP: Add support for Big Endian Mmio
> > APIs)
> > > > > > > >
> > > > > > > > We have started this discussion before and
> > the
> > > > > > > suggestion was to
> > > > > > > > create a separate .inf file keeping APIs name
> > same e.g.
> > > > > > > > MmioRead/MmioWrite in MdePkg.
> > > > > > > >
> > > > > > > > But we can't go with this approach (reason
> > mentioned
> > > > > > > by Udit).
> > > > > > > >
> > > > > > > > So please suggest if we should keep this
> > library
> > > > > > > under Platform/NXP
> > > > > > > > or I send a new patch moving this library in
> > MdePkg.
> > > > > > > >
> > > > > > > > But we have to keep a different name for Big
> > Endian
> > > > > > > MMIO APIs.
> > > > > > > >
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > > Meenakshi
> > > > > > > >
> > > > > > > >
> > > > > > > > > -----Original Message-----
> > > > > > > > > From: Udit Kumar
> > > > > > > > > Sent: Monday, October 23, 2017 12:38 PM
> > > > > > > > > To: Gao, Liming <liming.gao@intel.com>;
> > Meenakshi
> > > > > > > Aggarwal
> > > > > > > > > <meenakshi.aggarwal@nxp.com>; Ard
> > Biesheuvel
> > > > > > > > > <ard.biesheuvel@linaro.org>; Kinney,
> > Michael D
> > > > > > > > > <michael.d.kinney@intel.com>; edk2-
> > > > > > > devel@lists.01.org
> > > > > > > > > Subject: RE: [edk2] [PATCH 1/1]
> > MdePkg/IoLib: Add
> > > > > > > support for big-endian
> > > > > > > > > MMIO
> > > > > > > > >
> > > > > > > > > Hi Meenakshi/Liming,
> > > > > > > > > My 2 cents, around this.
> > > > > > > > >
> > > > > > > > > 1)
> > > > > > > > > Having a new lib for BE read might not be
> > helpful
> > > > > > > for us, e.g. a IP which is in
> > > > > > > > > BE mode access the UART for print or system
> > > > > > > registers which are in LE, then
> > > > > > > > > with new Lib, we will get all read/write in
> > BE mode
> > > > > > > > >
> > > > > > > > > 2)
> > > > > > > > > Especially for our IPs, which are changing
> > from BE
> > > > > > > to LE depending on
> > > > > > > > > platform.
> > > > > > > > > As said before, having BE read lib with API
> > name of
> > > > > > > MmioRead32 etc, will not
> > > > > > > > > help (I guess Meenakshi already seen some
> > problems
> > > > > > > around this) Adding a
> > > > > > > > > new lib with MmioRead32BE API name could
> > help, but
> > > > > > > IP driver we need to
> > > > > > > > > take care of IP mode either by Pcd or
> > #define, to
> > > > > > > select MmioRead32 or
> > > > > > > > > MmioRead32BE.
> > > > > > > > > This conditional compile needs to be done
> > for all
> > > > > > > IPs (which works in BE/LE
> > > > > > > > > mode on different platforms).
> > > > > > > > >
> > > > > > > > > My preferred way of implementation to use
> > one
> > > > > > > function in IP driver, And
> > > > > > > > > based on IP mode, do the switch.
> > > > > > > > >
> > > > > > > > > New Lib could have function like below
> > > > > > > > > MmioRead32Generic(IN  UINTN     Address,
> > BOOL
> > > > > > > IsIPBE) {
> > > > > > > > >    UINT32                            Value;
> > > > > > > > >
> > > > > > > > >    ASSERT ((Address & 3) == 0);
> > > > > > > > >    Value = *(volatile UINT32*)Address;
> > > > > > > > >    If(IsIPBE)
> > > > > > > > >      Value = SwapBytes32(Value);  return
> > Value; }
> > > > > > > > >
> > > > > > > > > And IP driver can use it
> > > > > > > > > MmioRead32Generic(ADDR,
> > > > > > > > > FixedPcdGet(This_IP_Mode_For_This_platform)
> > > > > > > > >
> > > > > > > > > Comments are welcome.
> > > > > > > > >
> > > > > > > > > Regards
> > > > > > > > > Udit
> > > > > > > > >
> > > > > > > > > > -----Original Message-----
> > > > > > > > > > From: edk2-devel [mailto:edk2-devel-
> > > > > > > bounces@lists.01.org] On Behalf Of
> > > > > > > > > > Gao, Liming
> > > > > > > > > > Sent: Monday, October 16, 2017 8:48 AM
> > > > > > > > > > To: Meenakshi Aggarwal
> > > > > > > <meenakshi.aggarwal@nxp.com>; Ard Biesheuvel
> > > > > > > > > > <ard.biesheuvel@linaro.org>; Kinney,
> > Michael D
> > > > > > > > > > <michael.d.kinney@intel.com>; edk2-
> > > > > > > devel@lists.01.org
> > > > > > > > > > Subject: Re: [edk2] [PATCH 1/1]
> > MdePkg/IoLib: Add
> > > > > > > support for
> > > > > > > > > > big-endian MMIO
> > > > > > > > > >
> > > > > > > > > > Meenakshi:
> > > > > > > > > >   I suggest to introduce new IoLib
> > library
> > > > > > > instance, not to add new IoLib
> > > > > > > > > APIs.
> > > > > > > > > > New IoLib library instance will perform
> > IO
> > > > > > > operation as the big
> > > > > > > > > > endian. You can update
> > > > > > > MdePkg/Library/BaseIoLibIntrinsic instance, add
> > > > > > > > > > new source file and new INF for it.
> > > > > > > > > >
> > > > > > > > > > UINT32
> > > > > > > > > > EFIAPI
> > > > > > > > > > MmioRead32 (
> > > > > > > > > >   IN  UINTN     Address
> > > > > > > > > >   )
> > > > > > > > > > {
> > > > > > > > > >   UINT32
> > Value;
> > > > > > > > > >
> > > > > > > > > >   ASSERT ((Address & 3) == 0);
> > > > > > > > > >   Value = *(volatile UINT32*)Address;
> > > > > > > > > >   return SwapBytes32(Value); }
> > > > > > > > > >
> > > > > > > > > > Thanks
> > > > > > > > > > Liming
> > > > > > > > > > >-----Original Message-----
> > > > > > > > > > >From: Meenakshi Aggarwal
> > > > > > > [mailto:meenakshi.aggarwal@nxp.com]
> > > > > > > > > > >Sent: Friday, October 13, 2017 2:07 PM
> > > > > > > > > > >To: Ard Biesheuvel
> > <ard.biesheuvel@linaro.org>;
> > > > > > > Kinney, Michael D
> > > > > > > > > > ><michael.d.kinney@intel.com>; edk2-
> > > > > > > devel@lists.01.org; Gao, Liming
> > > > > > > > > > ><liming.gao@intel.com>
> > > > > > > > > > >Subject: RE: [edk2] [PATCH 1/1]
> > MdePkg/IoLib:
> > > > > > > Add support for
> > > > > > > > > > >big-endian MMIO
> > > > > > > > > > >
> > > > > > > > > > >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
> > > > > > > > > >
> > _______________________________________________
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