linux-kernel - Re: Microblaze noMMU/MMU merge

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Message-ID: <20090421082523.GA19864@uranus.ravnborg.org>
Date:	Tue, 21 Apr 2009 10:25:23 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Michal Simek <michal.simek@...alogix.com>
Cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-arch@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: Microblaze noMMU/MMU merge

On Tue, Apr 21, 2009 at 09:45:47AM +0200, Michal Simek wrote:
> Hi All,
> 
> 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 */

Use dedicated header files for nommu / mmu only when it is really necessary.

In headers that are _NOT_ exported you can use CONFIG_MMU to test
if you are building for MMU or not - which is more readable.
 
The reason why you cannot use CONFIG_MMU in exported headers
are that CONFIG_MMU is not valid in the userspace headers (not set/unset).

In the optimal case you have no conditionals in the exported haders
and then just use CONFIG_MMU all over.

	Sam

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