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Re: [PATCH 26/30] loongson: flush irq write operation

To: yanh <yanh@lemote.com>
Subject: Re: [PATCH 26/30] loongson: flush irq write operation
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 20 May 2009 08:07:19 +0100
Cc: Wu Zhangjin <wuzhangjin@gmail.com>, linux-mips@linux-mips.org, Arnaud Patard <apatard@mandriva.com>, loongson-dev@googlegroups.com, zhangfx@lemote.com, Philippe Vachon <philippe@cowpig.ca>, Zhang Le <r0bertz@gentoo.org>, Erwan Lerale <erwan@thiscow.com>
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On Wed, May 20, 2009 at 10:28:14AM +0800, yanh wrote:

> I have test this patch just now. It works well on yeeloong. 

Thanks for testing.

> I have one question what's the difference between the two patch? 

Uncached writes can't be re-ordered.  By adding a read after the last
write my patch forces not only completion of the preceding write but due
to this ordering constraint also completion of all preceding writes is
enforced.

I/O space writes are slow.  I mean slower than slugs in space.  So my
patch is an optimization but that was not the point; I really only meant
to verify that we understood what's going on and we seem to.  Now let's
fix the real issue and make outX() non-posted.

  Ralf

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