[PATCH] ARM: decompressor: clear SCTLR.A bit for v7 cores

Nicolas Pitre nicolas.pitre at linaro.org
Thu Oct 11 11:58:15 EDT 2012

On Thu, 11 Oct 2012, Russell King - ARM Linux wrote:

> On Thu, Oct 11, 2012 at 08:31:47AM -0500, Rob Herring wrote:
> > This only affects v7 cores. It should not vary for v7 cores as unaligned
> > access is a required feature. So how is it going to vary on v7 CPUs?
> > We've got bigger problems if there are v7 cores that don't handle
> > unaligned accesses.
> Oh, and this gives me a third reason to NAK this patch.  Why only ensure
> that the A bit is clear for v7 CPUs?  Why not v6, v5, v4 too?  Why does
> ARMv7 get this special treatment?

As I said, gcc knows that ARMv7 can perform word sized accesses even 
with misaligned pointers.  So when it is passed a pointer marked with 
the packed attribute, it will generate a series of byte accesses when 
compiling for anything but ARMv7, and use a single ldr or str when 
compiling for ARMv7.


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