linux-kernel - Re: [PATCH 0/4] allow drivers to flush in-flight DMA

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Message-ID: <adabqbpted3.fsf@cisco.com>
Date:	Wed, 26 Sep 2007 12:29:12 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Grant Grundler <grundler@...isc-linux.org>
Cc:	akepner@....com, Jesse Barnes <jbarnes@...tuousgeek.org>,
	Jes Sorensen <jes@....com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org,
	James Bottomley <James.Bottomley@...eleye.com>
Subject: Re: [PATCH 0/4] allow drivers to flush in-flight DMA

 > Can we define this API to provide the same semantics as the memory
 > that dma_alloc_coherent() returns?

No, definitely not.  The property of the mapping here is all about
ordering with respect to other DMAs (from the same device) and nothing
to do with coherency between the CPU's and device's view of the memory.

 > Sorry - this feels like a "color of the shed" argument, but isn't
 > this about DMA ordering attribute?
 > "dmaflush" is an action and not an attribute to me.

I guess I don't love the "dmaflush" name, but the property of these
mappings is exactly that DMA into one of these mappings also performs
the action of flushing other in-flight DMAs.  However I guess your
point is a good one: the effect really desired is that DMAs to these
mappings become visible strictly after earlier DMAs, and we don't care
exactly how the effect is obtained.

No good idea of a better name though.

 - R.
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