staging: comedi: pcl812: simplify the dma->size calculations

The dma->size calculations are overly complicated in this driver and the
'prealloc_bufsz' sanity checks are unnecessary.

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/pcl812.c

@@ -512,8 +512,6 @@ struct pcl812_private {
 	unsigned int last_ai_chanspec;
 	unsigned char mode_reg_int;	/*  there is stored INT number for some card */
 	unsigned int ai_poll_ptr;	/*  how many sampes transfer poll */
-	unsigned int dma_runs_to_end;	/*  how many times we must switch DMA buffers */
-	unsigned int last_dma_run;	/*  how many bytes to transfer on last DMA buffer */
 	unsigned int max_812_ai_mode0_rangewait;	/*  setling time for gain */
 	unsigned int divisor1;
 	unsigned int divisor2;
@@ -544,71 +542,48 @@ static void pcl812_ai_setup_dma(struct comedi_device *dev,
 {
 	struct pcl812_private *devpriv = dev->private;
 	struct comedi_isadma *dma = devpriv->dma;
-	struct comedi_isadma_desc *desc0 = &dma->desc[0];
-	struct comedi_isadma_desc *desc1 = &dma->desc[1];
-	struct comedi_cmd *cmd = &s->async->cmd;
+	struct comedi_isadma_desc *desc = &dma->desc[0];
 	unsigned int bytes;
+	unsigned int nsamples;
 
-	/*  we use EOS, so adapt DMA buffer to one scan */
-	if (devpriv->ai_eos) {
-		desc0->size = comedi_bytes_per_scan(s);
-		desc1->size = comedi_bytes_per_scan(s);
-		devpriv->dma_runs_to_end = 1;
-	} else {
-		desc0->size = desc0->maxsize;
-		desc1->size = desc1->maxsize;
-		if (s->async->prealloc_bufsz < desc0->maxsize)
-			desc0->size = s->async->prealloc_bufsz;
-		if (s->async->prealloc_bufsz < desc1->maxsize)
-			desc1->size = s->async->prealloc_bufsz;
-		if (cmd->stop_src == TRIG_NONE) {
-			devpriv->dma_runs_to_end = 1;
-		} else {
-			/*  how many samples we must transfer? */
-			bytes = cmd->stop_arg * comedi_bytes_per_scan(s);
-
-			/*  how many DMA pages we must fill */
-			devpriv->dma_runs_to_end = bytes / desc0->size;
-
-			/* on last dma transfer must be moved */
-			devpriv->last_dma_run = bytes % desc0->size;
-			if (devpriv->dma_runs_to_end == 0)
-				desc0->size = devpriv->last_dma_run;
-			devpriv->dma_runs_to_end--;
-		}
-	}
-	if (desc0->size > desc0->maxsize) {
-		desc0->size = desc0->maxsize;
-		devpriv->ai_eos = 0;
-	}
-	if (desc1->size > desc1->maxsize) {
-		desc1->size = desc1->maxsize;
-		devpriv->ai_eos = 0;
-	}
 	dma->cur_dma = 0;
 
-	comedi_isadma_program(desc0);
+	/* if using EOS, adapt DMA buffer to one scan */
+	bytes = devpriv->ai_eos ? comedi_bytes_per_scan(s) : desc->maxsize;
+
+	nsamples = comedi_bytes_to_samples(s, bytes);
+	nsamples = comedi_nsamples_left(s, nsamples);
+	desc->size = comedi_samples_to_bytes(s, nsamples);
+	comedi_isadma_program(desc);
 }
 
 static void pcl812_ai_setup_next_dma(struct comedi_device *dev,
-				     struct comedi_subdevice *s)
+				     struct comedi_subdevice *s,
+				     unsigned int unread_samples)
 {
 	struct pcl812_private *devpriv = dev->private;
 	struct comedi_isadma *dma = devpriv->dma;
 	struct comedi_isadma_desc *desc;
+	unsigned int bytes;
+	unsigned int max_samples;
+	unsigned int nsamples;
 
 	comedi_isadma_disable(dma->chan);
-	dma->cur_dma = 1 - dma->cur_dma;
 
+	dma->cur_dma = 1 - dma->cur_dma;
 	desc = &dma->desc[dma->cur_dma];
-	if (!devpriv->ai_eos) {
-		if (devpriv->dma_runs_to_end)
-			devpriv->dma_runs_to_end--;
-		else
-			desc->size = devpriv->last_dma_run;
-	}
 
-	comedi_isadma_program(desc);
+	/* if using EOS, adapt DMA buffer to one scan */
+	bytes = devpriv->ai_eos ? comedi_bytes_per_scan(s) : desc->maxsize;
+
+	max_samples = comedi_bytes_to_samples(s, bytes);
+	nsamples = max_samples + unread_samples;
+	nsamples = comedi_nsamples_left(s, nsamples);
+	if (nsamples > max_samples) {
+		nsamples -= max_samples;
+		desc->size = comedi_samples_to_bytes(s, nsamples);
+		comedi_isadma_program(desc);
+	}
 }
 
 static void pcl812_ai_set_chan_range(struct comedi_device *dev,
@@ -879,13 +854,13 @@ static void pcl812_handle_dma(struct comedi_device *dev,
 	unsigned int nsamples;
 	int bufptr;
 
-	pcl812_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;
 
+	pcl812_ai_setup_next_dma(dev, s, nsamples);
+
 	transfer_from_dma_buf(dev, s, desc->virt_addr, bufptr, nsamples);
 }