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Re: [PATCH 0/2] FLATMEM: allow memory to start at pfn != 0 [take #2]

To: Franck Bui-Huu <vagabon.xyz@gmail.com>
Subject: Re: [PATCH 0/2] FLATMEM: allow memory to start at pfn != 0 [take #2]
From: peter fuerst <post@pfrst.de>
Date: Fri, 9 Mar 2007 14:18:40 +0100 (CET)
Cc: linux-mips <linux-mips@linux-mips.org>
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to detail Thomas' note...

On Tue, 6 Mar 2007, Franck Bui-Huu wrote:

> Date: Tue, 6 Mar 2007 22:39:59 +0100
> From: Franck Bui-Huu <vagabon.xyz@gmail.com>
> To: mbizon@freebox.fr
> Cc: linux-mips <linux-mips@linux-mips.org>
> Subject: Re: [PATCH 0/2] FLATMEM: allow memory to start at pfn != 0 [take
>     #2]
> ...
> In your case, you said:
>
>         PAGE_OFFSET = 0x80000000
>         PHYS_OFFSET = 0x10000000
>
> this means that the first kernel virtual address is 0x80000000 and the
> corresponding physical address is 0x10000000. If you load your kernel
> at 0x9000xxxx, it will be loaded in physical memory located at
> 0x2000xxxx which is obviously not what you want.
>

Never. If the kernel virtual address is 0x80000000+off with 0 <= off <=
0x1fffffff (aka kseg0, defined by bits 31..29), the corresponding physical
address is always 0+off, no matter what PHYS_OFFSET you invent. Physical
memory at 0x20000000 is not reachable from kesg0/1.

> ...

regards

peter

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