Re: [PATCH v0 1/2] DMA: fsldma: Disable DMA_INTERRUPT when Async_tx enabled

["Ira W. Snyder" <iws@ovro.caltech.edu>]

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 <Vishnu@freescale.com> wrote:
> > 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 <Vishnu@freescale.com>
> > ---
> >  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