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dmaengine: virt-dma: don't always free descriptor upon completion

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This patch attempts to enhance the case of a transfer submitted multiple
times, and where the cost of creating the descriptors chain is not
negligible.

This happens with big video buffers (several megabytes, ie. several
thousands of linked descriptors in one scatter-gather list). In these
cases, a video driver would want to do :
 - tx = dmaengine_prep_slave_sg()
 - dma_engine_submit(tx);
 - dma_async_issue_pending()
 - wait for video completion
 - read video data (or not, skipping a frame is also possible)
 - dma_engine_submit(tx)
   => here, the descriptors chain recalculation will take time
   => the dma coherent allocation over and over might create holes in
      the dma pool, which is counter-productive.
 - dma_async_issue_pending()
 - etc ...

In order to cope with this case, virt-dma is modified to prevent freeing
the descriptors upon completion if DMA_CTRL_ACK flag is set in the
transfer.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
This commit is contained in:
Robert Jarzmik
2015-05-26 23:06:33 +02:00
committed by Vinod Koul
parent e1031dc1f7
commit b9855f03d5
2 changed files with 25 additions and 7 deletions
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19
drivers/dma/virt-dma.c
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@@ -29,7 +29,7 @@ dma_cookie_t vchan_tx_submit(struct dma_async_tx_descriptor *tx)
spin_lock_irqsave(&vc->lock, flags);
cookie = dma_cookie_assign(tx);
list_add_tail(&vd->node, &vc->desc_submitted);
list_move_tail(&vd->node, &vc->desc_submitted);
spin_unlock_irqrestore(&vc->lock, flags);
dev_dbg(vc->chan.device->dev, "vchan %p: txd %p[%x]: submitted\n",
@@ -83,8 +83,10 @@ static void vchan_complete(unsigned long arg)
cb_data = vd->tx.callback_param;
list_del(&vd->node);
vc->desc_free(vd);
if (async_tx_test_ack(&vd->tx))
list_add(&vd->node, &vc->desc_allocated);
else
vc->desc_free(vd);
if (cb)
cb(cb_data);
@@ -96,9 +98,13 @@ void vchan_dma_desc_free_list(struct virt_dma_chan *vc, struct list_head *head)
while (!list_empty(head)) {
struct virt_dma_desc *vd = list_first_entry(head,
struct virt_dma_desc, node);
list_del(&vd->node);
dev_dbg(vc->chan.device->dev, "txd %p: freeing\n", vd);
vc->desc_free(vd);
if (async_tx_test_ack(&vd->tx)) {
list_move_tail(&vd->node, &vc->desc_allocated);
} else {
dev_dbg(vc->chan.device->dev, "txd %p: freeing\n", vd);
list_del(&vd->node);
vc->desc_free(vd);
}
}
}
EXPORT_SYMBOL_GPL(vchan_dma_desc_free_list);
@@ -108,6 +114,7 @@ void vchan_init(struct virt_dma_chan *vc, struct dma_device *dmadev)
dma_cookie_init(&vc->chan);
spin_lock_init(&vc->lock);
INIT_LIST_HEAD(&vc->desc_allocated);
INIT_LIST_HEAD(&vc->desc_submitted);
INIT_LIST_HEAD(&vc->desc_issued);
INIT_LIST_HEAD(&vc->desc_completed);