staging: comedi: pcl711: remove "empty acquisition" async command

This driver currently allows a cmd->stop_src == TRIG_COUNT with a cmd->stop_arg
of 0. This causes the (*do_cmd) to immediately generate a COMEDI_CB_EOA event
without acquiring any data.

This "empty acquisition" async command is not really useful. Validate that the
cmd->stop_arg is >= 1 in the (*do_cmdtest) and remove the "empty acquisition"
code.
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/pcl711.c

@@ -334,7 +334,9 @@ static int pcl711_ai_cmdtest(struct comedi_device *dev,
 	err |= cfc_check_trigger_arg_is(&cmd->convert_arg, 0);
 	err |= cfc_check_trigger_arg_is(&cmd->scan_end_arg, cmd->chanlist_len);
 
-	if (cmd->stop_src == TRIG_NONE)
+	if (cmd->stop_src == TRIG_COUNT)
+		err |= cfc_check_trigger_arg_min(&cmd->stop_arg, 1);
+	else	/* TRIG_NONE */
 		err |= cfc_check_trigger_arg_is(&cmd->stop_arg, 0);
 
 	if (err)
@@ -376,15 +378,8 @@ static int pcl711_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 
 	pcl711_set_changain(dev, s, cmd->chanlist[0]);
 
-	if (cmd->stop_src == TRIG_COUNT) {
-		if (cmd->stop_arg == 0) {
-			/* an empty acquisition */
-			s->async->events |= COMEDI_CB_EOA;
-			comedi_event(dev, s);
-			return 0;
-		}
+	if (cmd->stop_src == TRIG_COUNT)
 		devpriv->ntrig = cmd->stop_arg;
-	}
 
 	if (cmd->scan_begin_src == TRIG_TIMER) {
 		pcl711_ai_load_counters(dev);