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Re: SMP8634 DRAM memory issue

To: linux-mips@reliableembeddedsystems.com
Subject: Re: SMP8634 DRAM memory issue
From: David Daney <ddaney@avtrex.com>
Date: Sat, 20 Sep 2008 00:07:10 -0700
Cc: linux-mips@linux-mips.org, linux-mips@reliabeembeddedsystems.com
In-reply-to: <4e9ae533d87732773b7ad0f1a33b54f9@reliableembeddedsystems.com>
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References: <4e9ae533d87732773b7ad0f1a33b54f9@reliableembeddedsystems.com>
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linux-mips@reliableembeddedsystems.com wrote:
> Hi,
> 
> We've got an SMP8634 based set-top box from a 3rd party and are trying to
> port some middleware to it.
> Everything seems to work out fine, except for one thing ... the amount of
> memory for kernel space.
> 
> The box physically has two 64MB chips and two 32MB chips.  
> The kernel is only seeing the two 32MB chips, apparently attached to DRAM0.
> 
> The problem is the following:
> 
> 1) The middleware requires more memory in kernel space to allocalte big
> graphical surfaces.
> 2) Whatever runs before the kernel is also from a 3rd party and we don't
> have access to it.
> 3) We can't change anything on the box hardware.
> 
> This means, we would only be able to patch starting from the Linux kernel.
> 
> Do you see any way to swap what the kernel sees to be 128MB instead of 64MB
> and the user space 64MB minus whatever is allocated for the initial RAM
> disc?
> The 64MB for user space are sufficient, we just need more then 64 MB on
> kernel space.
> 

It depends if the 128MB is on DRAM0 or DRAM1.  Typically DRAM1 is not
usable by the kernel, although others have tried to access it as high-mem.

If DRAM0 is 128MB, *and* you have access to the kernel command line, you
 might try to append something like 'mem=96M'.  You may need to leave
some space in DRAM0 for the media components.  If not try jacking it up
to mem=128M.  Said media components do need memory too, so it may not be
possible to get more for the kernel and have it all work together.

David Daney

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