On Thu, Oct 15, 2009 at 06:25:14PM -0700, Dan Williams wrote:

[ added Leo and Timur to the Cc ]

On Wed, Oct 14, 2009 at 11:41 PM, Vishnu Suresh [off-list ref] wrote:

quoted

This patch disables the use of DMA_INTERRUPT capability with Async_tx

The fsldma produces a null transfer with DMA_INTERRUPT
capability when used with Async_tx. When RAID devices queue
a transaction via Async_tx, this  results in a hang.

Signed-off-by: Vishnu Suresh <redacted>
---
 drivers/dma/fsldma.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
index 296f9e7..66d9b39 100644
--- a/drivers/dma/fsldma.c
+++ b/drivers/dma/fsldma.c

@@ -1200,7 +1200,13 @@ static int __devinit of_fsl_dma_probe(struct of_device *dev,

                                               - fdev->reg.start + 1);

       dma_cap_set(DMA_MEMCPY, fdev->common.cap_mask);
+#ifndef CONFIG_ASYNC_CORE
+       /*
+        * The DMA_INTERRUPT async_tx is a NULL transfer, which will
+        * triger a PE interrupt.
+        */
       dma_cap_set(DMA_INTERRUPT, fdev->common.cap_mask);
+#endif
       dma_cap_set(DMA_SLAVE, fdev->common.cap_mask);
       fdev->common.device_alloc_chan_resources = fsl_dma_alloc_chan_resources;
       fdev->common.device_free_chan_resources = fsl_dma_free_chan_resources;

You are basically saying that fsl_dma_prep_interrupt() is buggy.  Can
that routine be fixed rather than this piecemeal solution?  If it
cannot be fixed (i.e. hardware issue) then fsl_dma_prep_interrupt()
should just be disabled/deleted altogether.

For what it's worth, I've used the following code in the recent past,
without any issues. This was on an 83xx, within the last few kernel
releases. I haven't tried it on the latest -rc.

Using device_prep_dma_memcpy() can trigger a callback as well, so the
interrupt feature isn't strictly needed. Just attach the callback to the
last memcpy operation.

static dma_cookie_t dma_async_interrupt(struct dma_chan *chan,
                                        dma_async_tx_callback callback,
                                        void *data)
{
        struct dma_device *dev = chan->device;
        struct dma_async_tx_descriptor *tx; 

        /* Set up the DMA */
        tx = dev->device_prep_dma_interrupt(chan, DMA_PREP_INTERRUPT);
        if (!tx)
                return -ENOMEM;

        tx->callback = callback;
        tx->callback_param = data;

        return tx->tx_submit(tx);
}

Ira