[U-Boot] [PATCH 12/16] efi_loader: Add DCACHE_OFF support for arm64

[Tom Rini]

On Tue, Feb 02, 2016 at 03:55:17PM +0000, Mark Rutland wrote:
> On Tue, Feb 02, 2016 at 03:45:10AM +0100, Alexander Graf wrote:
> > On arm64, boards can declare that they want to run with dcache disabled.
> > 
> > However, uEFI guarantees to payloads that they're running with the dcache
> > enabled which on arm64 means that they can do unaligned accesses.
> > 
> > To not leave those systems out of the door, let's handle the unaligned traps.
> > In the typical boot case, the OS will set up page tables and dcache itself
> > early on anyway once it's done talking with uEFI.
> 
> This is not sufficient to emulate having caches enabled.
> 
> There are other things which operate differently with the caches on
> (e.g. exclusives and/or atomics, which a compiler might generate
> implicitly).
> 
> Likewise, cache-maintenance by Va (which you may require from the
> I-side) implicitly hazards against cacheable accesses, but not against
> non-cacheable accesses.
> 
> There are almsot certainly other differences.
> 
> Due to that, I don't think this is a good approach.
> 
> Why can we not map memory using cacheable attributes in all cases?

I have a simpiler question perhaps, why can we not just say that this
support (in Kconfig that is) depends on !SYS_DACHE_OFF ?  Yes, only ARC
as moved that symbol over to Kconfig but that's a relatively easy thing
to remedy.  I assume that it being off on some systems is more of a
debug / bringup thing that needs to be circled back to rather than a
good hard requirement of the platform.

-- 
Tom
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