linux-kernel - Re: Memory-mapped I/O barriers, state of affairs?

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Message-ID: <c384c5ea1003221512s229d1d94ta7690d109b75843a@mail.gmail.com>
Date:	Mon, 22 Mar 2010 23:12:40 +0100
From:	Leon Woestenberg <leon.woestenberg@...il.com>
To:	Leon Woestenberg <leon.woestenberg@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Memory-mapped I/O barriers, state of affairs?

Hello Andreas, all,

On Mon, Mar 22, 2010 at 9:16 PM, Andreas Bombe <aeb@...ian.org> wrote:
> On Mon, Mar 22, 2010 at 08:18:49PM +0100, Leon Woestenberg wrote:
>> What is the current solution for that particular problem, i.e. how
>> should I make sure host memory writes are committed before I have an
>> external DMA device act on it?
>
> The dma_sync_* functions, if you reuse DMA buffers without unmapping,
> take care of that.  Otherwise the process of mapping them handles it.
>
The mapping makes the memory cache-coherent. I already use that.

But does that mean that this coherency is guaranteed to occur before I
start MMIO access to a device, i.e. is there a guaranteed ordering
between the writes?

Regards,
-- 
Leon
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