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From: Kumar Gala <galak@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
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Subject: Re: [RFC][PATCH] initial port of fixmap over from x86 for ppc32
Date: Mon, 7 Apr 2008 16:36:05 -0500
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Cc: linuxppc-dev@ozlabs.org, Paul Mackerras <paulus@samba.org>,
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On Apr 7, 2008, at 11:20 AM, Scott Wood wrote:
> On Mon, Apr 07, 2008 at 08:09:57AM -0500, Kumar Gala wrote:
>> On Apr 6, 2008, at 6:48 PM, Paul Mackerras wrote:
>>> More generally, I think we need to take an overall look at what  
>>> things
>>> we are using fixed virtual addresses for, and why they need to be
>>> fixed.  If there are indeed several such things then we can  
>>> introduce
>>> the fixmap stuff.
>>
>> The list as I see it:
>> * kmap
>> * pci-e config for 4xx/83xx
>> * kexec/kdump (ben commented on this when Dale posted his patches for
>> ppc32 support)
>>
>> future:
>> * possible usage by HV
>>
>> since we already have three users and a possible fourth it seems  
>> like a
>> useful change.
>
> Another possible use is a BAT/TLB1 mapping for SoC registers (or  
> anything
> else on the board which is frequently accessed), which can be reused  
> by
> ioremap() to avoid wasting normal TLB entries, and to facilitate early
> debugging.

x86 has an early ioremap() that is implemented on top of their fixmap  
usage that we could also steal if desired :)

- k