[edk2-devel] [edk2-discuss] Need memory barriers in IoLib for AARCH64

[Wasim Khan]

> -----Original Message-----
> From: Laszlo Ersek <lersek at redhat.com>
> Sent: Monday, July 13, 2020 9:02 PM
> To: devel at edk2.groups.io; afish at apple.com; Wasim Khan
> <wasim.khan at nxp.com>
> Cc: Mike Kinney <michael.d.kinney at intel.com>; liming.gao at intel.com; Leif
> Lindholm (Nuvia address) <leif at nuviainc.com>
> Subject: Re: [edk2-devel] [edk2-discuss] Need memory barriers in IoLib for
> AARCH64
> 
> On 07/12/20 18:54, Andrew Fish via groups.io wrote:
> >
> >
> >> On Jul 11, 2020, at 10:17 PM, Wasim Khan <wasim.khan at nxp.com> wrote:
> >>
> >> Hello
> >>
> >> Any comments ?
> >>
> >
> > I don’t see IoLibArm.c in master? I see IoLibNoIo.c.
> 
> That's due to the rename in commit 089e9c19a8c1
> ("MdePkg/BaseIoLibIntrinsic: Rename IoLibArm.c=>IoLibNoIo.c", 2020-05-07),
> which has been first included in edk2-stable202005.
> 
> I think Ard is away at the moment, so I'm adding Leif to the CC list.
> 
> Thanks
> Laszlo
> 
> > The MMIO function look like ARM assembler with the correct barrier
> instructions. The IO operations in this lib are the x86 in/out instructions, so they
> just ASSERT on ARM.
> >
> > On the X86 MemoryFence() is just a serializing intrinsic for the compiler to
> prevent optimizations from breaking the code, kind of like how you need to
> make MMIO as volatile in C.
> >
> > Thanks,
> >
> > Andrew Fish

Thank you Andrew and Laszlo for you response. 
My problem was that because there is no MemoryFence() in MmioRead/Write functions in IoLibNoIo.c, I was facing some serializing problem with AARCH64.
I have two options:
Either put MemoryFence() in my code under edl2-platforms before and after MmioRead/Write calls
OR
Add the MemoryFence() in MmioRead/Write itself for IoLibNoIo.c, like it is done for IoLib.c . Because I don’t see any harm to make sure that MmioRead/Write operation are serialized by using MemoryFence() in it. 

I prefer later option, if there is no specific reason for not adding MemoryFence() for IoLibNoIo.c.

> >
> >>> -----Original Message-----
> >>> From: Wasim Khan
> >>> Sent: Friday, July 10, 2020 6:20 PM
> >>> To: michael.d.kinney at intel.com; liming.gao at intel.com;
> >>> devel at edk2.groups.io
> >>> Subject: [edk2-discuss] Need memory barriers in IoLib for AARCH64
> >>>
> >>> Hello,
> >>>
> >>> MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsic.inf:
> >>> IoLib library uses IoLibArm.c for AARCH64/ARM architecture and
> >>> IoLib.c for other architectures.
> >>>
> >>> While IoLib.c already has memory barriers in MmioWrite functions,
> >>> there barriers are missing in IoLibArm.c Is there any reason for
> >>> **not** adding these memory barriers in IoLibArm.c to guarantee that
> >>> all MMIO operations are serialized ?
> >>>
> >>> I am facing some issues and I need to add memory barriers in
> >>> IoLibArm.c for
> >>> AARCH64 also .
> >>>
> >>>
> >>> Regards,
> >>> Wasim
> >>
> >>
> >>
> >
> >
> > 
> >
> >


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