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

[Leon Woestenberg]

Hello Andreas, all,

On Mon, Mar 22, 2010 at 9:16 PM, Andreas Bombe <aeb@xxxxxxxxxx> 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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