Re: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)

[Greg Ungerer <gerg@snapgear.com>]

Robin Getz wrote:
> On Thu 3 May 2007 07:03, Greg Ungerer pondered:
> > Robin Getz wrote:
> > > On Wed 2 May 2007 07:32, Greg Ungerer pondered:
> > > > Robin Getz wrote:
> > > > > I was trying to understand why we don't want to do the same checking on
> > > > > noMMU?
> > > > The problem is on systems that have RAM mapped at high physical
> > > > addresses. TASK_SIZE may well be a numerically smaller number
> > > > than the address range that RAM sits in. So this test fails when
> > > > it shouldn't.
> > > So, then this is a problem only on one or two architectures, not all
> > > noMMU platforms?
> > Its not an architecture problem. It can effect any board that
> > has RAM mapped at a large numerical addresses (larger than TASK_SIZE).
> > So it can effect any non-MMU platform.
>
> Depending on how TASK_SIZE is defined - it looks like everyone else forces it 
> to end of memory, except 68k[nommu].
>
> asm-arm/memory.h:#define TASK_SIZE              (CONFIG_DRAM_SIZE)
> asm-blackfin/processor.h:#define TASK_SIZE      (memory_end)
> asm-frv/mem-layout.h:#define TASK_SIZE                  __UL(0xFFFFFFFFUL)
>
> asm-m68k/processor.h:#define TASK_SIZE  (0xF0000000UL)
> asm-m68k/processor.h:#define TASK_SIZE  (0x0E000000)
> asm-m68k/processor.h:#define TASK_SIZE  (0x0E000000UL)
> asm-m68knommu/processor.h:#define TASK_SIZE     (0xF0000000UL)

Probably too:

asm-sh/processor.h:#define TASK_SIZE    0x7c000000UL

which has some parts with MMU.

There have been others out of tree that have it like this to.


> I'm happy to learn we are doing something wrong, but I think that we just 
> copied the arm/frv setup.

That is one way to handle it. Have you followed all the other
uses of TASK_SIZE and verified it is not a problem?

Regards
Greg



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