Query: Multiple Mappings to Mem and ARMV6+

[Russell King - ARM Linux]

On Thu, Feb 16, 2012 at 05:15:20PM +0000, Catalin Marinas wrote:
> On Thu, Feb 16, 2012 at 04:41:02PM +0000, viresh kumar wrote:
> > Sorry for starting the long old thread again, but i have to start it as i
> > was a bit confused. :(
> > 
> > We know that we can't have multiple mappings with different attributes
> > to the same physical memory on ARMv6+ machines due to speculative
> > prefetch.
> > 
> > So, we have following kind of mappings in kernel now (please correct me
> > if i am wrong):
> > - Low Mem: Mapped at boot time to - Normal Cacheable - Bufferable
> > - ioremap() - blocked on Low Mem, so that we don't create Device type mapping
> > to same mem
> > - dma_alloc_coherent() and others:
> >          - Without DMA_MEM_BUFFERABLE selected - gives strongly ordered mem
> >           (i.e. Non cacheable - Non Bufferable)
> >          - With DMA_MEM_BUFFERABLE selected - gives Normal - Non cacheable -
> >            Bufferable mapping
> >          - Maybe some other too...
> > 
> > I have a doubt with the last mapping mentioned above. We have two
> > mappings possibly to the same physical memory, with different
> > attributes: One is Cacheable and other one is not.
> > 
> > Is this allowed by ARM? Because the patch in which Russell blocked
> > ioremap on Low Mem, he clearly mentioned that these attributes are
> > also important and they should be same.
> 
> Section A3.5.7 in the latest ARM ARM (revC) clarifies the mismatched

There's a new version?