staging: comedi: dt282x: introduce dt282x_ao_setup_dma()

Introduce a helper function to read the analog output samples from the
async buffer and prep the DMA.

Use comedi_buf_read_samples() to read the analog output samples from
the async buffer.
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>

drivers/staging/comedi/drivers/dt282x.c

@@ -449,13 +449,29 @@ static void dt282x_munge(struct comedi_device *dev,
 	}
 }
 
+static unsigned int dt282x_ao_setup_dma(struct comedi_device *dev,
+					struct comedi_subdevice *s,
+					int cur_dma)
+{
+	struct dt282x_private *devpriv = dev->private;
+	void *ptr = devpriv->dma[cur_dma].buf;
+	unsigned int nsamples = devpriv->dma_maxsize / bytes_per_sample(s);
+	unsigned int nbytes;
+
+	nbytes = comedi_buf_read_samples(s, ptr, nsamples);
+	if (nbytes)
+		dt282x_prep_ao_dma(dev, cur_dma, nbytes);
+	else
+		dev_err(dev->class_dev, "AO underrun\n");
+
+	return nbytes;
+}
+
 static void dt282x_ao_dma_interrupt(struct comedi_device *dev,
 				    struct comedi_subdevice *s)
 {
 	struct dt282x_private *devpriv = dev->private;
 	int cur_dma = devpriv->current_dma_index;
-	void *ptr = devpriv->dma[cur_dma].buf;
-	int size;
 
 	outw(devpriv->supcsr | DT2821_SUPCSR_CLRDMADNE,
 	     dev->iobase + DT2821_SUPCSR_REG);
@@ -464,13 +480,8 @@ static void dt282x_ao_dma_interrupt(struct comedi_device *dev,
 
 	devpriv->current_dma_index = 1 - cur_dma;
 
-	size = cfc_read_array_from_buffer(s, ptr, devpriv->dma_maxsize);
-	if (size == 0) {
-		dev_err(dev->class_dev, "AO underrun\n");
+	if (!dt282x_ao_setup_dma(dev, s, cur_dma))
 		s->async->events |= COMEDI_CB_OVERFLOW;
-	} else {
-		dt282x_prep_ao_dma(dev, cur_dma, size);
-	}
 }
 
 static void dt282x_ai_dma_interrupt(struct comedi_device *dev,
@@ -916,26 +927,15 @@ static int dt282x_ao_inttrig(struct comedi_device *dev,
 {
 	struct dt282x_private *devpriv = dev->private;
 	struct comedi_cmd *cmd = &s->async->cmd;
-	int size;
 
 	if (trig_num != cmd->start_src)
 		return -EINVAL;
 
-	size = cfc_read_array_from_buffer(s, devpriv->dma[0].buf,
-					  devpriv->dma_maxsize);
-	if (size == 0) {
-		dev_err(dev->class_dev, "AO underrun\n");
+	if (!dt282x_ao_setup_dma(dev, s, 0))
 		return -EPIPE;
-	}
-	dt282x_prep_ao_dma(dev, 0, size);
 
-	size = cfc_read_array_from_buffer(s, devpriv->dma[1].buf,
-					  devpriv->dma_maxsize);
-	if (size == 0) {
-		dev_err(dev->class_dev, "AO underrun\n");
+	if (!dt282x_ao_setup_dma(dev, s, 1))
 		return -EPIPE;
-	}
-	dt282x_prep_ao_dma(dev, 1, size);
 
 	outw(devpriv->supcsr | DT2821_SUPCSR_STRIG,
 	     dev->iobase + DT2821_SUPCSR_REG);