staging: comedi: ni_pcidio: Mark buffer for writing when setting up DMA.

When setting up the DMA for 'read' streaming acquisition on the DIO
subdevice, mark the whole buffer as writable before starting the DMA.
This prevents a spurious detection of a DMA overwrite of good data
during the first interrupt.

Problem reported by Nicholas Nell.  Fix suggested by Frank Mori Hess.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/ni_pcidio.c b/drivers/staging/comedi/drivers/ni_pcidio.c
index 045a4c00f3462c5d3266eb88e4fa206bfdb6b72b..c9e5f2b2dfbb445dc52c47efcd680d648195e845 100644 (file)
--- a/drivers/staging/comedi/drivers/ni_pcidio.c
+++ b/drivers/staging/comedi/drivers/ni_pcidio.c
@@ -1012,6 +1012,9 @@ static int setup_mite_dma(struct comedi_device *dev, struct comedi_subdevice *s)
 
        devpriv->di_mite_chan->dir = COMEDI_INPUT;
 
+       /* write alloc the entire buffer */
+       comedi_buf_write_alloc(s->async, s->async->prealloc_bufsz);
+
        mite_prep_dma(devpriv->di_mite_chan, 32, 32);
 
        mite_dma_arm(devpriv->di_mite_chan);