dmaengine: rcar-dmac: use list_add() on rcar_dmac_desc_put()

For each descriptor, in addition to the memory used by the descriptors
structure itself, the driver allocates a list of chunks as well as a
buffer for hardware descriptors. Descriptors themselves are preallocated,
and allocation of the chunks and buffer is performed the first time the
descriptor is used. The memory isn't freed when the transfer is completed,
as the chunks and buffer will be needed again when the descriptor is
reused internally, so the driver keeps the memory around.

If only a few descriptors are used concurrently, the current
list_add_tail() implementation will result in all preallocated descriptors
being used before going back to the first one, and will thus allocate
chunks and a buffer for all preallocated descriptors. Using list_add()
will put the complete descriptor at the head of the list of available
descriptors, so the next transfer will be more likely to reuse a
descriptor that already has associated memory instead of one that has
never been used before.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index dfb17926297bd4f095a77b8105725335fa7c1aff..433e982604148644e27d910dcd70517c7ed8285a 100644 (file)
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -510,7 +510,7 @@ static void rcar_dmac_desc_put(struct rcar_dmac_chan *chan,
 
        spin_lock_irqsave(&chan->lock, flags);
        list_splice_tail_init(&desc->chunks, &chan->desc.chunks_free);
-       list_add_tail(&desc->node, &chan->desc.free);
+       list_add(&desc->node, &chan->desc.free);
        spin_unlock_irqrestore(&chan->lock, flags);
 }