On Jul 13, 2020, at 8:31 AM, Laszlo Ersek <lersek@redhat.com> wrote:

On 07/12/20 18:54, Andrew Fish via groups.io wrote:

On Jul 11, 2020, at 10:17 PM, Wasim Khan <wasim.khan@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

-----Original Message-----
From: Wasim Khan
Sent: Friday, July 10, 2020 6:20 PM
To: michael.d.kinney@intel.com; liming.gao@intel.com; devel@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