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staging: comedi: das16: fix DMA size for short transfers 

Currently this driver alwasy programs the DMA transfer to be the allocated
size of the DMA buffer. When the async command 'stop_src' is TRIG_COUNT its
possible (likely) for the last transfer to be less than the buffer size.

Introduce a helper function, das16_ai_setup_dma(), to calculate the actual
size of the DMA transfer based on the number of samples remaining and the
number of unread samples.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
H Hartley Sweeten 2015-01-26 16:17:20 -07:00 committed by Greg Kroah-Hartman
parent 42c44682a5
commit 1dc6e72903
1 changed files with 25 additions and 9 deletions
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34
drivers/staging/comedi/drivers/das16.c
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@ -448,6 +448,28 @@ struct das16_private_struct {
unsigned int timer_running:1;
};
static void das16_ai_setup_dma(struct comedi_device *dev,
struct comedi_subdevice *s,
unsigned int unread_samples)
{
struct das16_private_struct *devpriv = dev->private;
struct comedi_isadma *dma = devpriv->dma;
struct comedi_isadma_desc *desc = &dma->desc[dma->cur_dma];
unsigned int max_samples = comedi_bytes_to_samples(s, desc->maxsize);
unsigned int nsamples;
/*
* Determine dma size based on the buffer size plus the number of
* unread samples and the number of samples remaining in the command.
*/
nsamples = comedi_nsamples_left(s, max_samples + unread_samples);
if (nsamples > unread_samples) {
nsamples -= unread_samples;
desc->size = comedi_samples_to_bytes(s, nsamples);
comedi_isadma_program(desc);
}
}
static void das16_interrupt(struct comedi_device *dev)
{
struct das16_private_struct *devpriv = dev->private;
@ -486,13 +508,9 @@ static void das16_interrupt(struct comedi_device *dev)
nsamples = comedi_bytes_to_samples(s, nbytes);
/* restart DMA if more samples are needed */
if (nsamples && nsamples < comedi_nsamples_left(s, nsamples + 1)) {
struct comedi_isadma_desc *nxt_desc;
if (nsamples) {
dma->cur_dma = 1 - dma->cur_dma;
nxt_desc = &dma->desc[dma->cur_dma];
nxt_desc->size = nxt_desc->maxsize;
comedi_isadma_program(nxt_desc);
das16_ai_setup_dma(dev, s, nsamples);
}
spin_unlock_irqrestore(&dev->spinlock, spin_flags);
@ -672,7 +690,6 @@ static int das16_cmd_exec(struct comedi_device *dev, struct comedi_subdevice *s)
const struct das16_board *board = dev->board_ptr;
struct das16_private_struct *devpriv = dev->private;
struct comedi_isadma *dma = devpriv->dma;
struct comedi_isadma_desc *desc = &dma->desc[0];
struct comedi_async *async = s->async;
struct comedi_cmd *cmd = &async->cmd;
unsigned int byte;
@ -721,8 +738,7 @@ static int das16_cmd_exec(struct comedi_device *dev, struct comedi_subdevice *s)
/* set up dma transfer */
dma->cur_dma = 0;
desc->size = desc->maxsize;
comedi_isadma_program(desc);
das16_ai_setup_dma(dev, s, 0);
/* set up timer */
spin_lock_irqsave(&dev->spinlock, flags);