firmwareload fails for cortex-m7 on imx8mp

[Ahmad Fatoum]

Hello Stefano,

On 15.11.24 14:43, Stefano Manni wrote:
> Dear all,
> 
> I cannot run an ELF image on the M7 core on the imx8mp soc.
> The ELF comes from zephyr and it runs as expected when I load it from linux,
> but in barebox I encounter this error:
> 
> barebox at NXP i.MX8MPlus EVK board:/ tftp zephyr.elf
>         [################################################################]
> barebox at NXP i.MX8MPlus EVK board:/ firmwareload zephyr.elf
> remoteproc0: powering up remoteproc-cm7.of
> DABT (current EL) exception (ESR 0x96000061) at 0x00000000007e0004

https://esr.arm64.dev/#0x96000061 decodes this as
"Abort caused by writing to memory" (Alignment fault) with valid FAR.

FAR is the addresss listed here (0x00000000007e0004), which is indeed
not divisible by 8.

> [<ffd826f4>] (__arch_memcpy+0x48/0x13c) from [<ffd82a00>] (memcpy+0xc/0x14)

The optimized memcpy used here expects misalignment not to trap.

> As you can see the exception happens when rproc_elf_load_segments() tries to
> memcpy a segment where the M7 expects it. The ELF has been compiled to run
> from ITCM memory (0x007E0000-0x007FFFFF).
> 
> Do you have any idea? Maybe may I have to put a reserved-memory for ITCM?

I think I may have broken this when I changed barebox to map everything outside
main memory as uncached.

I did this, because we 1) don't want to risk the main CPU speculating into I/O
memory and 2) don't want to have to use memory barriers for synchronization.

The flipside is that drivers that access I/O memory must do this via
readl/writel and friends or via memcpy_io/memset_io. This was already required
before, but some drivers that didn't do this were lucky enough to fly under
the radar. At least for remoteproc, this seems no longer the case.

I just Cc'd you on a patch to fix this for remoteproc.
Please let me know with a Tested-by if this resolves your issue.

Cheers,
Ahmad

> 
> Thank you.
> 
> Best,
> Stefano
> 
> 


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