linux-kernel - Re: Opinion on ordering of writel vs. stores to RAM

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Message-ID: <yq0venufslz.fsf@jaguar.mkp.net>
Date:	11 Sep 2006 09:19:36 -0400
From:	Jes Sorensen <jes@....com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	David Miller <davem@...emloft.net>, jeff@...zik.org,
	paulus@...ba.org, torvalds@...l.org, linux-kernel@...r.kernel.org,
	akpm@...l.org, segher@...nel.crashing.org, jeremy@....com
Subject: Re: Opinion on ordering of writel vs. stores to RAM

>>>>> "Ben" == Benjamin Herrenschmidt <benh@...nel.crashing.org> writes:

Ben> On Sun, 2006-09-10 at 23:23 +0100, Alan Cox wrote:
>> Ar Llu, 2006-09-11 am 07:25 +1000, ysgrifennodd Benjamin
>> Herrenschmidt: > I'm copying that from a private discussion I
>> had. Please let me know if > you have comments. This proposal
>> includes some questions too so please > answer :)
>> 
>> Looks sane and Linus seems to like mmiowb. Only other question:
>> what are the guarantees of memcpy_to/fromio. Does it access the
>> memory in ordered fashion or not, does it guarantee only ordering
>> at the end of the copy or during it ?

Ben> Well, Linus is also ok with writel not ordering memory an IO
Ben> accesses :) Though he also mentioned that if we go that route
Ben> (which is what we have now in fact), we take the burden of having
Ben> to test and fix drivers who don't get it...

We have to do this on SN2 anyway, so this way we can benefit from
each other's work :)

Cheers,
Jes
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