staging: comedi: pcl816: simplify the dma->size calculations

Currently this driver determines the number of DMA "runs" needed and the size
of the "last" DMA transfer in order to perform a command. As long as there are
more "runs" required, the dma->size is set to the buffer maxsize. On the last
"run" the buffer is set to the "last" size.

Refactor the driver to use the comedi core helpers to determine the DMA size
based on the buffer maxsize and the number of samples remaining in the command.

This allows removing the 'dma_runs_to_end' and 'last_dma_run' mamebers from
the private data.
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/pcl816.c

@@ -115,8 +115,6 @@ static const struct pcl816_board boardtypes[] = {
 
 struct pcl816_private {
 	struct comedi_isadma *dma;
-	long dma_runs_to_end;	/*  how many we must permorm DMA transfer to end of record */
-	unsigned long last_dma_run;	/*  how many bytes we must transfer on last DMA page */
 	unsigned int ai_poll_ptr;	/*  how many sampes transfer poll */
 	unsigned int divisor1;
 	unsigned int divisor2;
@@ -149,53 +147,47 @@ static void pcl816_ai_setup_dma(struct comedi_device *dev,
 	struct pcl816_private *devpriv = dev->private;
 	struct comedi_isadma *dma = devpriv->dma;
 	struct comedi_isadma_desc *desc = &dma->desc[0];
-	struct comedi_cmd *cmd = &s->async->cmd;
-
-	if (cmd->stop_src == TRIG_COUNT) {
-		/*  how many */
-		desc->size = cmd->stop_arg * comedi_bytes_per_scan(s);
-
-		/*  how many DMA pages we must fill */
-		devpriv->dma_runs_to_end = desc->size / desc->maxsize;
-
-		/* on last dma transfer must be moved */
-		devpriv->last_dma_run = desc->size % desc->maxsize;
-		devpriv->dma_runs_to_end--;
-		if (devpriv->dma_runs_to_end >= 0)
-			desc->size = desc->maxsize;
-	} else {
-		desc->size = desc->maxsize;
-		devpriv->dma_runs_to_end = -1;
-	}
+	unsigned int nsamples;
 
 	dma->cur_dma = 0;
 
+	/*
+	 * Determine dma size based on the buffer maxsize and the number of
+	 * samples remaining in the command.
+	 */
+	nsamples = comedi_bytes_to_samples(s, desc->maxsize);
+	nsamples = comedi_nsamples_left(s, nsamples);
+	desc->size = comedi_samples_to_bytes(s, nsamples);
 	comedi_isadma_program(desc);
 }
 
 static void pcl816_ai_setup_next_dma(struct comedi_device *dev,
-				     struct comedi_subdevice *s)
+				     struct comedi_subdevice *s,
+				     unsigned int unread_samples)
 {
 	struct pcl816_private *devpriv = dev->private;
-	struct comedi_cmd *cmd = &s->async->cmd;
 	struct comedi_isadma *dma = devpriv->dma;
+	struct comedi_isadma_desc *desc;
+	unsigned int max_samples;
+	unsigned int nsamples;
 
 	comedi_isadma_disable(dma->chan);
-	dma->cur_dma = 1 - dma->cur_dma;
-
-	/* switch dma bufs if still running */
-	if (devpriv->dma_runs_to_end > -1 || cmd->stop_src == TRIG_NONE) {
-		struct comedi_isadma_desc *desc = &dma->desc[dma->cur_dma];
 
-		if (devpriv->dma_runs_to_end)
-			desc->size = desc->maxsize;
-		else
-			desc->size = devpriv->last_dma_run;
+	dma->cur_dma = 1 - dma->cur_dma;
+	desc = &dma->desc[dma->cur_dma];
 
+	/*
+	 * Determine dma size based on the buffer maxsize plus the number of
+	 * unread samples and the number of samples remaining in the command.
+	 */
+	max_samples = comedi_bytes_to_samples(s, desc->maxsize);
+	nsamples = max_samples + unread_samples;
+	nsamples = comedi_nsamples_left(s, nsamples);
+	if (nsamples > unread_samples) {
+		nsamples -= unread_samples;
+		desc->size = comedi_samples_to_bytes(s, nsamples);
 		comedi_isadma_program(desc);
 	}
-
-	devpriv->dma_runs_to_end--;
 }
 
 static void pcl816_ai_set_chan_range(struct comedi_device *dev,
@@ -324,13 +316,13 @@ static irqreturn_t pcl816_interrupt(int irq, void *d)
 		return IRQ_HANDLED;
 	}
 
-	pcl816_ai_setup_next_dma(dev, s);
-
 	nsamples = comedi_bytes_to_samples(s, desc->size) -
 		   devpriv->ai_poll_ptr;
 	bufptr = devpriv->ai_poll_ptr;
 	devpriv->ai_poll_ptr = 0;
 
+	pcl816_ai_setup_next_dma(dev, s, nsamples);
+
 	transfer_from_dma_buf(dev, s, desc->virt_addr, bufptr, nsamples);
 
 	pcl816_ai_clear_eoc(dev);