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Re: [PATCH v2 22/22] bitops: remove minix bitops from asm/bitops.h

To: monstr@monstr.eu
Subject: Re: [PATCH v2 22/22] bitops: remove minix bitops from asm/bitops.h
From: Akinobu Mita <akinobu.mita@gmail.com>
Date: Fri, 22 Oct 2010 16:55:10 +0900
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>, Christoph Hellwig <hch@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Greg Ungerer <gerg@uclinux.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Roman Zippel <zippel@linux-m68k.org>, Andreas Schwab <schwab@linux-m68k.org>, linux-m68k@lists.linux-m68k.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com, linux-s390@vger.kernel.org, Yoshinori Sato <ysato@users.sourceforge.jp>, microblaze-uclinux@itee.uq.edu.au, "David S. Miller" <davem@davemloft.net>, sparclinux@vger.kernel.org, Hirokazu Takata <takata@linux-m32r.org>, linux-m32r@ml.linux-m32r.org, Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, Paul Mundt <lethal@linux-sh.org>, linux-sh@vger.kernel.org, Chris Zankel <chris@zankel.net>
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2010/10/22 Michal Simek <monstr@monstr.eu>:
> Akinobu Mita wrote:
>> minix bit operations are only used by minix filesystem and useless
>> by other modules. Because byte order of inode and block bitmaps is
>> defferent on each architecture like below:
>>
>> m68k:
>>       big-endian 16bit indexed bitmaps
>>
>> h8300, microblaze, s390, sparc, m68knommu:
>>       big-endian 32 or 64bit indexed bitmaps
>
> Just one small fix microblaze little endian support is ready for merging
> to mainline which means that microblaze is
> big-endian 32bit  and  little-endian 32bit
>
>>
>> m32r, mips, sh, xtensa:
>>       big-endian 32 or 64bit indexed bitmaps for big-endian mode
>>       little-endian bitmaps for little-endian mode
>>
>> Others:
>>       little-endian bitmaps
>>
>> In order to move minix bit operations from asm/bitops.h to
>> architecture independent code in minix file system, this provides two
>> config options.
>>
>> CONFIG_MINIX_FS_BIG_ENDIAN_16BIT_INDEXED is only selected by m68k.
>> CONFIG_MINIX_FS_NATIVE_ENDIAN is selected by the architectures which
>> use native byte order bitmaps (h8300, microblaze, s390, sparc,
>> m68knommu, m32r, mips, sh, xtensa).
>> The architectures which always use little-endian bitmaps do not select
>> these options.
>
> I haven't created any Kconfig option for little/big endian microblaze
> but there should be a little bit different handling for MINIX_FS_NATIVE_ENDIAN
> as you are describing above.
> Anyway I think you don't need to reflect this in your patch because
> we are not using that filesystem and I will write it to my to-do list and
> will fix it later.

If upcomming microblade little-endian mode will use little-endian
bitmaps for minixfs, microblade can continue to select
CONFIG_MINIX_FS_NATIVE_ENDIAN and you don't need to change it.

But if it will use big-endian bitmaps, it may need some extra work
to support it. Becuase there is no little-endian architecture
which uses bit-endian bitmaps for minixfs.

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