staging: comedi: quatech_daqp_cs: cleanup Step 3 of ai (*do_cmdtest)

Step 3 of the (*do_cmdtest) trivially validates the async command arguments.
The validations also modify the arguments if they are invalid so that the
user gets valid values if the test fails.

Reorder the checks so that if any of the checks fail proper values are
used for subsequent checks.
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/quatech_daqp_cs.c

@@ -141,6 +141,8 @@
 
 #define DAQP_FIFO_SIZE			4096
 
+#define DAQP_MAX_TIMER_SPEED		10000	/* 100 kHz in nanoseconds */
+
 struct daqp_private {
 	int stop;
 };
@@ -399,30 +401,30 @@ static int daqp_ai_cmdtest(struct comedi_device *dev,
 
 	err |= comedi_check_trigger_arg_is(&cmd->start_arg, 0);
 
-#define MAX_SPEED	10000	/* 100 kHz - in nanoseconds */
+	err |= comedi_check_trigger_arg_min(&cmd->chanlist_len, 1);
+	err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg,
+					   cmd->chanlist_len);
 
-	if (cmd->scan_begin_src == TRIG_TIMER) {
+	if (cmd->scan_begin_src == TRIG_TIMER)
 		err |= comedi_check_trigger_arg_min(&cmd->scan_begin_arg,
-						    MAX_SPEED);
-	}
-
-	/* If both scan_begin and convert are both timer values, the only
-	 * way that can make sense is if the scan time is the number of
-	 * conversions times the convert time
-	 */
-
-	if (cmd->scan_begin_src == TRIG_TIMER && cmd->convert_src == TRIG_TIMER
-	    && cmd->scan_begin_arg != cmd->convert_arg * cmd->scan_end_arg) {
-		err |= -EINVAL;
-	}
+						    DAQP_MAX_TIMER_SPEED);
 
 	if (cmd->convert_src == TRIG_TIMER) {
 		err |= comedi_check_trigger_arg_min(&cmd->convert_arg,
-						    MAX_SPEED);
-	}
+						    DAQP_MAX_TIMER_SPEED);
 
-	err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg,
-					   cmd->chanlist_len);
+		if (cmd->scan_begin_src == TRIG_TIMER) {
+			/*
+			 * If both scan_begin and convert are both timer
+			 * values, the only way that can make sense is if
+			 * the scan time is the number of conversions times
+			 * the convert time.
+			 */
+			arg = cmd->convert_arg * cmd->scan_end_arg;
+			err |= comedi_check_trigger_arg_is(&cmd->scan_begin_arg,
+							   arg);
+		}
+	}
 
 	if (cmd->stop_src == TRIG_COUNT)
 		err |= comedi_check_trigger_arg_max(&cmd->stop_arg, 0x00ffffff);