linux-kernel - Re: [PATCH] [POWERPC] Improve (in|out)

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Date:	Tue, 20 May 2008 17:16:59 -0400
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Trent Piepho <tpiepho@...escale.com>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	Scott Wood <scottwood@...escale.com>
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code


On Tue, 2008-05-20 at 13:40 -0700, Trent Piepho wrote:
> There was some discussion on a Freescale list if the powerpc I/O accessors
> should be strictly ordered w.r.t.  normal memory.  Currently they are not.  It
> does not appear as if any other architecture's I/O accessors are strictly
> ordered in this manner.  memory-barriers.txt explicitly states that the I/O
> space (inb, outw, etc.) are NOT strictly ordered w.r.t. normal memory
> accesses and it's implied the other I/O accessors (e.g., writel) are the same.
> 
> However, it is somewhat harder to program for this model, and there are almost
> certainly a number of drivers using coherent DMA which have subtle bugs because
> the do not include the necessary barriers.
> 
> But clearly and change to this would be a subject for a different patch.

The current accessors should provide all the necessary ordering
guarantees...

Ben.


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