linux-kernel - RE: [PATCH 01/18] dmaengine: add fence support

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Message-ID: <129600E5E5FB004392DDC3FB599660D7B5548783@irsmsx504.ger.corp.intel.com>
Date:	Tue, 15 Sep 2009 17:04:59 +0100
From:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>
Subject: RE: [PATCH 01/18] dmaengine: add fence support

Williams, Dan J wrote:
> Some engines optimize operation by reading ahead in the descriptor chain
> such that descriptor2 may start execution before descriptor1 completes.
> If descriptor2 depends on the result from descriptor1 then a fence is
> required (on descriptor2) to disable this optimization.  The async_tx
> api could implicitly identify dependencies via the 'depend_tx'
> parameter, but that would constrain cases where the dependency chain
> only specifies a completion order rather than a data dependency.  So,
> provide an ASYNC_TX_FENCE to explicitly identify data dependencies.
> 
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@...el.com>--
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