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[RESEND,2/2] Documentation: dmaengine: document DMA_CTRL_ACK

Message ID 1432674394-32007-3-git-send-email-robert.jarzmik@free.fr (mailing list archive)
State Accepted
Headers show

Commit Message

Robert Jarzmik May 26, 2015, 9:06 p.m. UTC 
Add documentation about acking the transfers, and their
reusability.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 Documentation/dmaengine/provider.txt | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Comments

Maxime Ripard June 8, 2015, 7:13 a.m. UTC | #1 
On Tue, May 26, 2015 at 11:06:34PM +0200, Robert Jarzmik wrote:
> Add documentation about acking the transfers, and their
> reusability.
> 
> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
> Cc: Maxime Ripard <maxime.ripard@free-electrons.com>

Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Thanks!
Maxime
diff mbox

Patch

diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt
index 05d2280..ca67b0f 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
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