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Re: [PATCH] MIPS: Bcm47xx: Fix 128MB RAM support

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] MIPS: Bcm47xx: Fix 128MB RAM support
From: Hauke Mehrtens <hauke@hauke-m.de>
Date: Mon, 22 Feb 2010 21:25:11 +0100
Cc: linux-mips@linux-mips.org
In-reply-to: <20100222191440.GA12818@linux-mips.org>
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References: <1266691880-372-1-git-send-email-hauke@hauke-m.de> <20100222191440.GA12818@linux-mips.org>
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Ralf Baechle wrote:
> On Sat, Feb 20, 2010 at 07:51:20PM +0100, Hauke Mehrtens wrote:
> 
>> Ignoring the last page when ddr size is 128M. Cached
>> accesses to last page is causing the processor to prefetch
>> using address above 128M stepping out of the ddr address
>> space.
> 
> Is this a hardware issue prefetching issue?  The kernel should not try
> CPU prefetch instructions at all on non-coherent CPUs such as the
> BCM47xx.

This is a hardware issue on the bcm47xx when 128MB ram is present. This
workaround is out of broadcom's kernel sources and is included in
OpenWRT for some months. Without this patch the kernel does not even
print out anything and with this patch it is working.

Hauke

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