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| author | Robert Jarzmik <robert.jarzmik@free.fr> | 2015-05-26 23:06:34 +0200 |
|---|---|---|
| committer | Vinod Koul <vinod.koul@intel.com> | 2015-06-17 18:46:15 +0200 |
| commit | 5f88d9706fa48084eaab2dbbec27779809c5106b (patch) | |
| tree | 2706a940b88555c4c3124c1a2551d1b125c0a97c /Documentation/dmaengine | |
| parent | dmaengine: virt-dma: don't always free descriptor upon completion (diff) | |
| download | linux-5f88d9706fa48084eaab2dbbec27779809c5106b.tar.xz linux-5f88d9706fa48084eaab2dbbec27779809c5106b.zip | |
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')
| -rw-r--r-- | Documentation/dmaengine/provider.txt | 11 |
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. * DMA_CTRL_ACK - - 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 -------------------- |