[RFC] tidspbridge: use a parameter to allocate shared memory

[Russell King - ARM Linux]

On Thu, Oct 07, 2010 at 09:40:12AM +0200, Laurent Pinchart wrote:
> Hi Omar,
> 
> On Thursday 07 October 2010 07:45:36 Omar Ramirez Luna wrote:
> > tidspbridge driver uses a block of memory denominated SHared Memory
> > to store info & communicate with DSP, this SHM needs to be physically
> > contiguous and non-cacheable,
> 
> There are non-cacheable mappings, but there's no such thing as non-cacheable 
> memory. Does the MPU mapping for that SHM block really needs to be non-
> cacheable, your could you instead flush the cache after writing to it 
> (performance issues might be involved, I don't know the details about that SHM 
> usage) ?

ARMv6 and above don't like having multiple mappings with different
memory type/shareability/cache attributes.  It's architecturally
forbidden.

So if you want non-cacheable memory and you want to be architecturally
compliant, you have to exclude it from the kernel's direct-mapped
memory mapping.