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

[Suresh Vishnu-B05022]

> -----Original Message-----
> From: Ira W. Snyder [mailto:iws@xxxxxxxxxxxxxxxx] 
> Sent: Friday, October 16, 2009 9:04 PM
> To: Dan Williams
> Cc: Suresh Vishnu-B05022; herbert@xxxxxxxxxxxxxxxxxxx; 
> linux-kernel@xxxxxxxxxxxxxxx; linux-raid@xxxxxxxxxxxxxxx; 
> linuxppc-dev@xxxxxxxxxx; linux-crypto@xxxxxxxxxxxxxxx; Tabi 
> Timur-B04825
> Subject: Re: [PATCH v0 1/2] DMA: fsldma: Disable 
> DMA_INTERRUPT when Async_tx enabled
> 
> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > ---
> > >  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.
We are working to fix this issue.
> > 
> 
> 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.
This works fine as long as only DMA_MEMCPY is being used.
The async_tx_channel_switch does not occur and the 
device_prep_dma_interrupt is not called. 
However, when a DMA_XOR capable device is exposed, 
which is differnet from the DMA_MEMCPY/INTERRUPT device, this path is hit.

Is it proper to schedule a dma_interrupt from the channel switch call, 
even when the depend_tx and tx channels correspond to different devices?

> 
> 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
> 
> 
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