path: root/Documentation/dmaengine
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authorRobert Jarzmik <robert.jarzmik@free.fr>2015-05-26 23:06:34 +0200
committerVinod Koul <vinod.koul@intel.com>2015-06-17 22:16:15 +0530
commit5f88d9706fa48084eaab2dbbec27779809c5106b (patch)
tree2706a940b88555c4c3124c1a2551d1b125c0a97c /Documentation/dmaengine
parentb9855f03d560d351e95301b9de0bc3cad3b31fe9 (diff)
Documentation: dmaengine: document DMA_CTRL_ACK
Add documentation about acking the transfers, and their reusability. Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com> Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Diffstat (limited to 'Documentation/dmaengine')
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt
index 05d2280190f1..ca67b0f04c6e 100644
--- a/Documentation/dmaengine/provider.txt
+++ b/Documentation/dmaengine/provider.txt
@@ -345,11 +345,12 @@ where to put them)
that abstracts it away.
- - Undocumented feature
- - No one really has an idea of what it's about, besides being
- related to reusing the DMA transaction descriptors or having
- additional transactions added to it in the async-tx API
- - Useless in the case of the slave API
+ - If set, the transfer can be reused after being completed.
+ - There is a guarantee the transfer won't be freed until it is acked
+ by async_tx_ack().
+ - As a consequence, if a device driver wants to skip the dma_map_sg() and
+ dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used,
+ it can resubmit the transfer right after its completion.
General Design Notes