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Date: Tue, 27 May 2008 09:28:30 -0600
From: Jonathan Corbet <corbet@lwn.net>
To: benh@kernel.crashing.org
Cc: Linux Arch list <linux-arch@vger.kernel.org>,
       David Miller <davem@davemloft.net>, scottwood@freescale.com,
       linuxppc-dev@ozlabs.org, alan@lxorguk.ukuu.org.uk,
       linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Trent Piepho <tpiepho@freescale.com>
Subject: Re: MMIO and gcc re-ordering issue
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On Tue, 27 May 2008 11:33:46 +1000
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> However, I'm using that as an excuse to bring back my pet subject,
> which is basically, should we instead just finally mandate the use of
> explicit rmb/wmb/mb's (which boils down to barrier() on x86) to
> drivers who want to order memory consistent accesses vs. MMIO ?

To me this seems like asking for a long series of weird bugs in
drivers.  Is the cost of a barrier in an MMIO operation so high that we
can't afford to just put them in?  Alan's suggestion of no-barrier
versions for people who know what they're doing (and who think there's a
reason to care) seems like a better way to go to me.

jon