[PATCH] ARM: decompressor: Fix mmu mapping for non-DRAM address space.

[Shilimkar, Santosh]

On Wed, May 9, 2012 at 5:53 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Wed, May 09, 2012 at 02:20:28PM +0530, Shilimkar, Santosh wrote:
>> The only change done common code is  clearing 'XN' bit for DRAM
>> region in page table entries. The other change of setting the DACR
>> register is done in ARMv7 specific code.
>
> Yes, XN is an ARMv6+ thing.  Before ARMv5, it was implementation defined.
>
> Some implementations used the bit to mean "allow writes to update the
> cache".  Other implementations labelled this bit as "should be zero"
> while others labelled it as "should be one".
>
Good to know.

> The upshot of this is, we know that having this bit as '1' means that
> all the CPUs we support today work.  I would be _very_ concerned to
> change this bit to zero as we _really_ don't know how the pre-ARMv6
> CPUs would react.
>
I agree.

> The solution to this is pretty simple - if ARMv6+ needs a different
> base section mapping value, then we need to extract that from the code
> and pass in the base section mapping value.
>
> I'll sort out a patch later today for this.
Great.

Regards
Santosh