2GB address space limit on 32-bit PowerPC Macintosh

[Kumar Gala]

On May 15, 2005, at 6:34 PM, Benjamin Herrenschmidt wrote:

> On Mon, 2005-05-16 at 09:29 +1000, Paul Mackerras wrote:
>  > Benjamin Herrenschmidt writes:
>  >
> > > We "inherited" from some historic junk in the prep and chrp 
> support,
>  > > that a lot of embedded platforms blindly copied, where archs use
>  > > io_block_mapping() early during boot to hard-wire various IO 
> stuffs in
>  > > various places in the address space, including just after 2Gb. 
> It's
>  > > totally bogus, but nobody really cared to fix it so far. The 2Gb
>  > > TASK_SIZE limit doesn't seem to have ever been an issue for ppc32 
> users
>  > > so far I must say, at least you are the first one to complain ;)
>  >
> > I believe that prep and chrp are also now OK with a 3GB TASK_SIZE
>  > limit, it's just various embedded board ports that will blow up with
>  > 3GB.  We should change the default to 3GB to encourage the embedded
>  > guys to fix their ports properly (or else to put in the appropriate
>  > Kconfig stuff to force it back to 2GB for their port).
>  >
>
>  static void __init
>  prep_map_io(void)
> {
>          io_block_mapping(0x80000000, PREP_ISA_IO_BASE, 0x10000000, 
> _PAGE_IO);
>          io_block_mapping(0xf0000000, PREP_ISA_MEM_BASE, 0x08000000, 
> _PAGE_IO);
>  }
>
> We need to fix that too :) Though I suppose we can just switch that to
>  page tables, I don't really see the point of using a BAT here...

Are the embedded board ports broken because of similar 
io_block_mapping() calls or for some other reason?

I'm in agreement that we should bump TASK_SIZE to 3GB and fix things, 
how about after 2.6.12 is out?

- kumar