[U-Boot] memcpy/memset on arm64 platforms

[Tom Rini]

On Mon, Jan 07, 2019 at 02:43:05PM +0530, Lokesh Vutla wrote:

> Hi All,
> 	I am trying to enable CONFIG_USE_ARCH_MEMSET/MEMCPY on arm64 platforms and
> realized that there is no arm64 specific memcpy available in u-boot. So I
> tried porting arm64 specific memcpy from kernel[1]. Memcpy stopped working
> after that and observed that if destination address is unaligned then system
> hangs.
> 
> After doing a bit more research, understood  that unaligned access to device
> or strongly ordered memories will fail. And the memory system (even normal
> RAM) behaves like strongly ordered memory when the MMU is disabled[2]. In
> u-boot MMU is enabled very late after relocation and SPL doesn't enable MMU
> at all.
> 
> Before I proceed any further wanted to hear from others if anyone have
> already tried and have any working solution. If not should we update the
> kernel memcpy to use unaligned destination address and use it in u-boot?
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/lib/memcpy.S
> [2] https://community.arm.com/processors/f/discussions/7557/when-and-where-will-the-ldp-instruction-trigger-an-exception

I suspect we should, yes.  Adding in some custodians of other arm64
platforms for comment.

-- 
Tom
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