staging: comedi: das16: factor out chanlist checking from (*do_cmdtest)

Step 5 of the (*do_cmdtest) validates that the cmd->chanlist is compatible
with the hardware.

For aesthetics, factor out the step 5 code for the analog input async command
support. Tidy up the factored out code.

To minimize the noise, change the dev_err() to dev_dbg().
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/das16.c

@@ -600,13 +600,40 @@ static void das16_timer_interrupt(unsigned long arg)
 		mod_timer(&devpriv->timer, jiffies + timer_period());
 }
 
+static int das16_ai_check_chanlist(struct comedi_device *dev,
+				   struct comedi_subdevice *s,
+				   struct comedi_cmd *cmd)
+{
+	unsigned int chan0 = CR_CHAN(cmd->chanlist[0]);
+	unsigned int range0 = CR_RANGE(cmd->chanlist[0]);
+	int i;
+
+	for (i = 1; i < cmd->chanlist_len; i++) {
+		unsigned int chan = CR_CHAN(cmd->chanlist[i]);
+		unsigned int range = CR_RANGE(cmd->chanlist[i]);
+
+		if (chan != ((chan0 + i) % s->n_chan)) {
+			dev_dbg(dev->class_dev,
+				"entries in chanlist must be consecutive channels, counting upwards\n");
+			return -EINVAL;
+		}
+
+		if (range != range0) {
+			dev_dbg(dev->class_dev,
+				"entries in chanlist must all have the same gain\n");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int das16_cmd_test(struct comedi_device *dev, struct comedi_subdevice *s,
 			  struct comedi_cmd *cmd)
 {
 	const struct das16_board *board = comedi_board(dev);
 	struct das16_private_struct *devpriv = dev->private;
 	int err = 0, tmp;
-	int gain, start_chan, i;
 	int mask;
 
 	/* Step 1 : check if triggers are trivially valid */
@@ -693,24 +720,10 @@ static int das16_cmd_test(struct comedi_device *dev, struct comedi_subdevice *s,
 	if (err)
 		return 4;
 
-	/*  check channel/gain list against card's limitations */
-	if (cmd->chanlist) {
-		gain = CR_RANGE(cmd->chanlist[0]);
-		start_chan = CR_CHAN(cmd->chanlist[0]);
-		for (i = 1; i < cmd->chanlist_len; i++) {
-			if (CR_CHAN(cmd->chanlist[i]) !=
-			    (start_chan + i) % s->n_chan) {
-				dev_err(dev->class_dev,
-					"entries in chanlist must be consecutive channels, counting upwards\n");
-				err++;
-			}
-			if (CR_RANGE(cmd->chanlist[i]) != gain) {
-				dev_err(dev->class_dev,
-					"entries in chanlist must all have the same gain\n");
-				err++;
-			}
-		}
-	}
+	/* Step 5: check channel list if it exists */
+	if (cmd->chanlist && cmd->chanlist_len > 0)
+		err |= das16_ai_check_chanlist(dev, s, cmd);
+
 	if (err)
 		return 5;