staging: comedi: das1800: tidy up das1800_ai_transfer_size()

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>

diff --git a/drivers/staging/comedi/drivers/das1800.c b/drivers/staging/comedi/drivers/das1800.c
index c36ce0c73c683944d5086ce7f18bbcd459dc488c..5be5162dfe69c8303149d7dfdff959aaaefcc2cd 100644 (file)
--- a/drivers/staging/comedi/drivers/das1800.c
+++ b/drivers/staging/comedi/drivers/das1800.c
@@ -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);