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Re: 64 bit kernel for BCM1250

To: Michael Belamina <belamina1@yahoo.com>
Subject: Re: 64 bit kernel for BCM1250
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Tue, 31 May 2005 15:57:13 +0100 (BST)
Cc: linux-mips@linux-mips.org
In-reply-to: <20050526185931.58037.qmail@web32510.mail.mud.yahoo.com>
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References: <20050526185931.58037.qmail@web32510.mail.mud.yahoo.com>
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On Thu, 26 May 2005, Michael Belamina wrote:

> I have tried the patch on kernel version 2.4.28 and it
> seems that the fix is not working for this kernel
> version. I used gcc version 2.95.4 and it is working. 

 Hmm, you may need additional fixes...  How about just switching to 2.6?  
Currently 2.4 is over 4 years old and it shouldn't be used for new 
development.

> 1. What is the best way to translate 32 bit ioctl
> codes to 64 bit?

 Use arch/mips64/kernel/ioctl32.c, but in 2.6 there may be a generic 
solution available.

> 2. How 64 bit kernel space buffers will  be used by a
> 32 bit application (using mmap)? 

 As usual.  Except you can't get more than 2GB of them.

> 3.What is the maximum usable ram out of 2GB I will
> have if I am using a 32 bit application and 64 bit
> kernel and the kernel is allocating the buffers using
> __get_free_pages (I need the buffers for DMA - and I
> need them to be physically continuous)?

 2GB minus what's used by Linux for other purposes.  Physically 
contiguous?  That sounds like a problem (and broken hardware)...

  Maciej

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