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RE: Using more than 256 MB of memory on SB1250 in 32-bit mode

To: "Steve Madsen" <madsen@tadpole.com>, <linux-mips@linux-mips.org>
Subject: RE: Using more than 256 MB of memory on SB1250 in 32-bit mode
From: "Finney, Steve" <Steve.Finney@SpirentCom.COM>
Date: Fri, 29 Aug 2003 16:40:58 -1000
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Thread-index: AcNueSiTz/62aUoOQay7j1spfQAwsQAJaNnA
Thread-topic: Using more than 256 MB of memory on SB1250 in 32-bit mode
Not sure what you mean by "system memory". You can turn on CONFIG_HIGHMEM and 
get access to 512 MB physical memory  or more on the BCM with a 32-bit kernel, 
but you can't access memory above the low 256 MB  directly through KSEG0/1, so 
there are some things that the kernel can't use it for (though it can be 
allocated to user processes). Also, since CONFIG_DISCONTIGMEM isn't supported, 
you end up wasting a bunch of RAM on useless page table space (36MB for 512 MB 
physical), and there's also some caching weirdness if you try and mmap() 
/dev/mem to get user access to the >0x10000000 I/O registers. Also, your 
startup will report "1792 MB HIGHMEM available".

sf

> -----Original Message-----
> From: Steve Madsen [mailto:madsen@tadpole.com]
> Sent: Friday, August 29, 2003 12:00 PM
> To: linux-mips@linux-mips.org
> Subject: Using more than 256 MB of memory on SB1250 in 32-bit mode
> 
> 
> Is it possible to use more than 256 MB of system memory with 
> the Broadcom 
> SB1250 in 32-bit mode?  The memory map I'm looking at shows 
> me that the 
> second 256 MB of memory is at physical address 0x80000000.  I 
> suspect that 
> due to the 2G/2G split in the kernel, I can't use memory this 
> high without 
> moving to the 64-bit kernel.
> 
> Would someone confirm this for me?
> 
> -- 
> Steve Madsen <madsen@tadpole.com>
> Tadpole Computer, Inc.  http://www.tadpole.com
> 
> 

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