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dmaengine: add fence support

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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@intel.com>
This commit is contained in:
Dan Williams 2009-09-08 17:42:50 -07:00
parent f9dd213437
commit 0403e38277
8 changed files with 79 additions and 41 deletions
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3
include/linux/async_tx.h
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@ -58,11 +58,14 @@ struct dma_chan_ref {
* array.
* @ASYNC_TX_ACK: immediately ack the descriptor, precludes setting up a
* dependency chain
* @ASYNC_TX_FENCE: specify that the next operation in the dependency
* chain uses this operation's result as an input
*/
enum async_tx_flags {
ASYNC_TX_XOR_ZERO_DST = (1 << 0),
ASYNC_TX_XOR_DROP_DST = (1 << 1),
ASYNC_TX_ACK = (1 << 2),
ASYNC_TX_FENCE = (1 << 3),
};
/**