linux-kernel - Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

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Message-ID: <46690A39.3010402@de.ibm.com>
Date:	Fri, 08 Jun 2007 09:50:17 +0200
From:	Carsten Otte <cotte@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>, carsteno@...ibm.com,
	Jared Hulbert <jaredeh@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	richard.griffiths@...driver.com,
	Richard Griffiths <res07ml0@...izon.net>,
	Linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

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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