Message-ID: <46690A39.3010402@de.ibm.com>
Date: Fri, 08 Jun 2007 09:50:17 +0200
From: Carsten Otte <cotte@de.ibm.com>
Reply-To: carsteno@de.ibm.com
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To: Christoph Hellwig <hch@infradead.org>, carsteno@de.ibm.com,
       Jared Hulbert <jaredeh@gmail.com>,
       Nick Piggin <nickpiggin@yahoo.com.au>,
       Andrew Morton <akpm@linux-foundation.org>,
       richard.griffiths@windriver.com,
       Richard Griffiths <res07ml0@verizon.net>, Linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP
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Christoph Hellwig wrote:
> We can have a simpler variant as a start if we really want.  But we
> need to pass it through the mtd layer.  There is a reason we have this
> thing called devices drivers, and we don't want to add knowledge of
> ioremap to the filesystems and have users find out physical addresses
> of their flash to pass it as mount option.
I see your poing with regard to layering, and I agree to it.
In order to do ioremap/iounmap at least we need a counterpart 
put_xip_page thing to do iounmap in that path. Our dcss segments on 
390 did not raise that requirement: they had a permanent kernel mapping.
The quiz question to me is: why don't we establish a permanenet 
mapping of the entire thing from mount() to unmount(). That eliminates 
the need to do iomap/iounmap, eliminates the need to have 
put_xip_page, and eliminates to care about what layer would do this. 
Would work for cramfs, won't work for read+write flash filesystems.
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