From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Mundt <lethal@linux-sh.org>
Subject: Re: Microblaze noMMU/MMU merge
Date: Tue, 21 Apr 2009 16:57:39 +0900
Message-ID: <20090421075738.GC15167@linux-sh.org>
References: <49ED79AB.10004@petalogix.com>
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To: Michal Simek <michal.simek@petalogix.com>
Cc: Ingo Molnar <mingo@elte.hu>, lkml <linux-arch@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>, Linux Kernel list <linux-kernel@vger.kernel.org>

On Tue, Apr 21, 2009 at 09:45:47AM +0200, Michal Simek wrote:
> I would like to say your opinion about putting together Microblaze MMU
> arch to noMMU version.
> 
> In C code will be #ifdef CONFIG_MMU ... #endif  or #ifndef.
> 
> Here is proposal for headers. The similar style is used in m68k but I
> would like to have the same code
> for both archs in main file.
> 
> #ifndef _ASM_MICROBLAZE_PAGE_H
> #define _ASM_MICROBLAZE_PAGE_H
> 
> code for noMMU and MMU which is the same for both.
> 
> #ifdef __uClinux__
> #include "page_no.h" -> noMMU specific
> #else
> #include "page_mm.h"-> MMU specific
> #endif
> #endif /* _ASM_MICROBLAZE_PAGE_H */
> 
There's really not that much code that you need to change in order to
support nommu, as long as you designed your architecture port to be
fairly compartmentalized. Take a look at some of the other architectures
in-tree that support both in the same architecture backend. sh was the
first to support a configurable CONFIG_MMU during the 2.5 days, but there
are others now as well (though I don't know how actively the others are
maintained -- nommu people tend to be even worse (!) than general
embedded people at hanging around).

In addition to sh, at least frv, m32r, and arm support a configurable
CONFIG_MMU these days. xtensa seems to have just recently joined the
club, too.