[U-Boot] memcpy/memset on arm64 platforms

[Marek Vasut]

On 1/11/19 5:13 PM, Tom Rini wrote:
> 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.

Why do you want a custom memcpy() implementation in the first place ?

>> 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.

The ARM64 MMU table setup seems to be a mess, it could indeed use some
improvement.

>> 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.

Does the unaligned access exception happen only before the MMU is
enabled or even after ?

-- 
Best regards,
Marek Vasut