[U-Boot] [PATCH v3 2/2] arm: add initial support for Amlogic Meson and ODROID-C2

[Beniamino Galvani]

On Mon, Apr 11, 2016 at 11:08:02PM +0200, Marek Vasut wrote:
> >>> +	val = fdt_getprop(gd->fdt_blob, offset, "reg", &len);
> >>> +	if (len < sizeof(*val) * 4)
> >>> +		return -EINVAL;
> >>> +
> >>> +	/* Don't use fdt64_t to avoid unaligned access */
> >>
> >> This looks iffy, can you elaborate on this issue ?
> > 
> > I was getting a "Synchronous Abort handler, esr 0x96000021" which
> > seemed to indicate a alignment fault, but thinking again about it I'm
> > not sure anymore of the real cause. fdt64_t and fdt64_to_cpu() don't
> > work here, I will try to investigate better why. Suggestions are
> > welcome :)
> 
> Toolchain issues ? Stack alignment issue ?

So, after some investigation, the reason is that the code runs when
caches are still disabled and thus all the memory is treated as
Device-nGnRnE, requiring aligned accesses. The return value of
fdt_getprop() is guaranteed to be aligned to a 4 byte boundary (but
not 8) and therefore a 32-bit type must be used to avoid alignment
faults. Probably the comment should be updated to explain this better.

Beniamino