MTD Mapping driver - out of vmalloc space

Jörn Engel joern at
Fri Apr 15 15:45:23 EST 2005

On Tue, 12 April 2005 11:07:38 +0100, Chris Elston wrote:
> Thanks for everyone's input on this, I've moved the kernel virtual
> base address to 0xa0000000, and it works fine now.  
> I'm still not convinced that this is a future proof solution 
> though.  What happens when I get a board with 512MB Flash 1GB SDRAM?
> I can push the top of the SDRAM out to the high mem area, but I'll 
> have to encroach further into user space to map the Flash.  There's
> no good reason that the whole of the Flash need be mapped at the same
> time. (Perhaps performance?)

Definitely performance.  At the end of the day, you need a bigger
namespace of some sorts.  Possible solutions are:

o a 64bit machine,
o a 4GiB/4GiB kernel/user split and
o a PPC440 with 36bit addressing and some hardware and ioremap tricks
  to move flash above the 32bit limit.

The 4/4 split also costs some performance.  It doesn't violate the
'flash read must be atomic' requirement, though.


-- more straw can't possibly matter...
-- Kirby Bakken

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