[PATCH] mxs/dma: Enlarge the CCW descriptor area to 4 pages

Russell King - ARM Linux linux at arm.linux.org.uk
Fri Sep 14 04:30:50 EDT 2012

On Fri, Sep 14, 2012 at 08:36:15AM +0530, Vinod Koul wrote:
> On Wed, 2012-09-05 at 03:46 +0200, Marek Vasut wrote:
> > One way to fix this is to recycle descriptors that were already used during the 
> > transfer, but can we really do it fast enough, so the DMA would do it's job at 
> > one end of the descriptor chain and we'd be building the other?
> See the comment in dma_ctrl_flags:
> * @DMA_CTRL_ACK - if clear, the descriptor cannot be reused until the client
> *  acknowledges receipt, i.e. has has a chance to establish any dependency
> *  chains
> Setting this would mean that driver can reuse the descriptor once the
> transaction has completed.

Actually, that has little meaning for slave DMA descriptors (other than
it should already be set for consistency with the async_tx stuff, which
has the above mentioned depenedency chains.)

Once completed, descriptors can be reused irrespective of the above flag.

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