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staging: comedi: das1800: tidy up das1800_ai_transfer_size()

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For aesthetics, pass the fill time 'ns' as a parameter to this function.

Refactor this function to calculate the transfer size in 'samples' instead
of 'bytes'. This removes the need to constantly multiply the values by the
'sample_size'. It also helps avoid any possible integer overflow issues.

Use the comedi_nsamples_left() helper to limit the samples when cmd->stop_src
is TRIG_COUNT.

Use comedi_samples_to_bytes() to return the final DMA size in bytes.

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 2015-01-13 10:16:44 -07:00 committed by Greg Kroah-Hartman
parent 620ec185a2
commit 5e5a21cf8e
1 changed files with 19 additions and 26 deletions
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45
drivers/staging/comedi/drivers/das1800.c
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@ -967,42 +967,35 @@ static void das1800_setup_counters(struct comedi_device *dev,
}
static unsigned int das1800_ai_transfer_size(struct comedi_device *dev,
struct comedi_subdevice *s)
struct comedi_subdevice *s,
unsigned int ns)
{
struct comedi_cmd *cmd = &s->async->cmd;
unsigned int size = DMA_BUF_SIZE;
unsigned int sample_size = comedi_bytes_per_sample(s);
unsigned int fill_time = 300000000; /* target time in nanoseconds for filling dma buffer */
unsigned int max_size; /* maximum size we will allow for a transfer */
unsigned int max_samples = comedi_bytes_to_samples(s, DMA_BUF_SIZE);
unsigned int samples;
/* make dma buffer fill in 0.3 seconds for timed modes */
samples = max_samples;
/* for timed modes, make dma buffer fill in 'ns' time */
switch (cmd->scan_begin_src) {
case TRIG_FOLLOW: /* not in burst mode */
case TRIG_FOLLOW: /* not in burst mode */
if (cmd->convert_src == TRIG_TIMER)
size = (fill_time / cmd->convert_arg) * sample_size;
samples = ns / cmd->convert_arg;
break;
case TRIG_TIMER:
size = (fill_time / (cmd->scan_begin_arg * cmd->chanlist_len)) *
sample_size;
break;
default:
size = DMA_BUF_SIZE;
samples = ns / (cmd->scan_begin_arg * cmd->chanlist_len);
break;
}
/* set a minimum and maximum size allowed */
max_size = DMA_BUF_SIZE;
/* if we are taking limited number of conversions, limit transfer size to that */
if (cmd->stop_src == TRIG_COUNT &&
cmd->stop_arg * cmd->chanlist_len * sample_size < max_size)
max_size = cmd->stop_arg * cmd->chanlist_len * sample_size;
/* limit samples to what is remaining in the command */
samples = comedi_nsamples_left(s, samples);
if (size > max_size)
size = max_size;
if (size < sample_size)
size = sample_size;
if (samples > max_samples)
samples = max_samples;
if (samples < 1)
samples = 1;
return size;
return comedi_samples_to_bytes(s, samples);
}
static void das1800_ai_setup_dma(struct comedi_device *dev,
@ -1017,8 +1010,8 @@ static void das1800_ai_setup_dma(struct comedi_device *dev,
devpriv->cur_dma = 0;
/* determine a reasonable dma transfer size */
bytes = das1800_ai_transfer_size(dev, s);
/* determine a dma transfer size to fill buffer in 0.3 sec */
bytes = das1800_ai_transfer_size(dev, s, 300000000);
dma->size = bytes;
das1800_isadma_program(dma);