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

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Message-ID: <4639E40D.6030809@snapgear.com>
Date:	Thu, 03 May 2007 23:30:53 +1000
From:	Greg Ungerer <gerg@...pgear.com>
To:	Robin Getz <rgetz@...ckfin.uclinux.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)

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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Greg Ungerer  --  Chief Software Dude       EMAIL:     gerg@...pgear.com
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