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

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Message-Id: <200705030735.36879.rgetz@blackfin.uclinux.org>
Date:	Thu, 3 May 2007 07:35:36 -0400
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Greg Ungerer" <gerg@...pgear.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)

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)

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

-Robin
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