From: ebiederm@xmission.com (Eric W. Biederman)
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Linux Kernel list <linux-kernel@vger.kernel.org>,
Jesse Barnes <jbarnes@virtuousgeek.org>,
"David S. Miller" <davem@davemloft.net>,
Jeff Garzik <jgarzik@pobox.com>,
Paul Mackerras <paulus@samba.org>,
Linus Torvalds <torvalds@osdl.org>, Andrew Morton <akpm@osdl.org>,
Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [RFC] MMIO accessors & barriers documentation
Date: Mon, 11 Sep 2006 23:48:33 -0600 [thread overview]
Message-ID: <m1pse17hzi.fsf@ebiederm.dsl.xmission.com> (raw)
In-Reply-To: <1157969261.23085.108.camel@localhost.localdomain> (Alan Cox's message of "Mon, 11 Sep 2006 11:07:41 +0100")
Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
>> > "Except where the underlying device is marked as cachable or
>> > prefetchable"
>>
>> You aren't supposed to use MMIO accessors on cacheable memory, are you ?
>
> Why not. Providing it is in MMIO space, consider ROMs for example or
> write path consider frame buffers.
Frame buffers are rarely cachable as such, on x86 they are usually
write-combining. Which means that the writes can be merged and
possibly reordered while they are being written but they can't be
cached. Most arches I believe have something that roughly corresponds
to write combining.
Ensuring we can still use this optimization to mmio space is
moderately important.
Eric
next prev parent reply other threads:[~2006-09-12 5:50 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-11 4:03 [RFC] MMIO accessors & barriers documentation Benjamin Herrenschmidt
2006-09-11 8:57 ` Alan Cox
2006-09-11 9:17 ` Benjamin Herrenschmidt
2006-09-11 10:07 ` Alan Cox
2006-09-11 9:59 ` Benjamin Herrenschmidt
2006-09-11 17:26 ` Alan Cox
2006-09-11 21:29 ` Benjamin Herrenschmidt
2006-09-12 5:48 ` Eric W. Biederman [this message]
2006-09-12 5:56 ` Benjamin Herrenschmidt
2006-09-12 6:27 ` Eric W. Biederman
2006-09-12 7:13 ` Benjamin Herrenschmidt
2006-09-12 15:19 ` Segher Boessenkool
2006-09-12 21:22 ` Benjamin Herrenschmidt
2006-09-13 0:12 ` Segher Boessenkool
2006-09-13 1:34 ` Benjamin Herrenschmidt
2006-09-11 18:39 ` Jesse Barnes
2006-09-11 21:45 ` Benjamin Herrenschmidt
2006-09-11 21:54 ` Jeff Garzik
2006-09-11 22:56 ` Benjamin Herrenschmidt
2006-09-11 23:08 ` Roland Dreier
2006-09-11 23:18 ` Benjamin Herrenschmidt
2006-09-11 23:24 ` Jeff Garzik
2006-09-12 0:46 ` Benjamin Herrenschmidt
2006-09-12 15:32 ` Segher Boessenkool
2006-09-11 22:05 ` Jesse Barnes
2006-09-11 23:01 ` Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2006-09-12 5:33 Albert Cahalan
2006-09-12 5:48 ` Benjamin Herrenschmidt
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