From 5f88d9706fa48084eaab2dbbec27779809c5106b Mon Sep 17 00:00:00 2001 From: Robert Jarzmik Date: Tue, 26 May 2015 23:06:34 +0200 Subject: [PATCH] Documentation: dmaengine: document DMA_CTRL_ACK Add documentation about acking the transfers, and their reusability. Signed-off-by: Robert Jarzmik Acked-by: Maxime Ripard Signed-off-by: Vinod Koul --- Documentation/dmaengine/provider.txt | 11 ++++++----- 1 file 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 --------------------