Commit bcfb7465 authored May 15, 2009 by Ira Snyder Committed by Li Yang May 22, 2009

fsldma: fix infinite loop on multi-descriptor DMA chain completion

When creating a DMA transaction with multiple descriptors, the async_tx
cookie is set to 0 for each descriptor in the chain, excluding the last
descriptor, whose cookie is set to -EBUSY.

When fsl_dma_tx_submit() is run, it only assigns a cookie to the first
descriptor. All of the remaining descriptors keep their original value,
including the last descriptor, which is set to -EBUSY.

After the DMA completes, the driver will update the last completed cookie
to be -EBUSY, which is an error code instead of a valid cookie. This causes
dma_async_is_complete() to always return DMA_IN_PROGRESS.

This causes the fsldma driver to never cleanup the queue of link
descriptors, and the driver will re-run the DMA transaction on the hardware
each time it receives the End-of-Chain interrupt. This causes an infinite
loop.

With this patch, fsl_dma_tx_submit() is changed to assign a cookie to every
descriptor in the chain. The rest of the code then works without problems.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Li Yang <leoli@freescale.com>

parent 138ef018

drivers/dma/fsldma.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -313,8 +313,8 @@ static void fsl_chan_toggle_ext_start(struct fsl_dma_chan *fsl_chan, int enable)

		static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx)
		{
		struct fsl_desc_sw *desc = tx_to_fsl_desc(tx);
		struct fsl_dma_chan *fsl_chan = to_fsl_chan(tx->chan);
		struct fsl_desc_sw *desc;
		unsigned long flags;
		dma_cookie_t cookie;

		@@ -322,14 +322,17 @@ static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx)
		spin_lock_irqsave(&fsl_chan->desc_lock, flags);

		cookie = fsl_chan->common.cookie;
		list_for_each_entry(desc, &tx->tx_list, node) {
		cookie++;
		if (cookie < 0)
		cookie = 1;

		desc->async_tx.cookie = cookie;
		fsl_chan->common.cookie = desc->async_tx.cookie;
		}

		append_ld_queue(fsl_chan, desc);
		list_splice_init(&desc->async_tx.tx_list, fsl_chan->ld_queue.prev);
		fsl_chan->common.cookie = cookie;
		append_ld_queue(fsl_chan, tx_to_fsl_desc(tx));
		list_splice_init(&tx->tx_list, fsl_chan->ld_queue.prev);

		spin_unlock_irqrestore(&fsl_chan->desc_lock, flags);

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