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... [2] https://community.arm.com/processors/f/discussions/7557/when-and-where-will-...
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 ?