staging: comedi: usbduxsigma: remove unused "convert" timing for AO

The `cmdtest` and `cmd` handlers for the AO subdevice
(`usbduxsigma_ao_cmdtest()` and `usbduxsigma_ao_cmd()`) support "scan"
timing of commands with all channels updated every "scan" period.  There
is some disabled code to use "convert" timing in high speed mode.  That
would allow channels to be updated sequentially every "convert" period.
Since that code is incomplete and currently disabled, remove it to
simplify the existing code.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: Bernd Porr <mail@berndporr.me.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxsigma.c

@@ -840,28 +840,20 @@ static int usbduxsigma_ao_cmdtest(struct comedi_device *dev,
 {
 	struct usbduxsigma_private *devpriv = dev->private;
 	int err = 0;
-	int high_speed;
-	unsigned int flags;
-
-	/* high speed conversions are not used yet */
-	high_speed = 0;		/* (devpriv->high_speed) */
 
 	/* Step 1 : check if triggers are trivially valid */
 
 	err |= comedi_check_trigger_src(&cmd->start_src, TRIG_NOW | TRIG_INT);
 
-	if (high_speed) {
-		/*
-		 * start immediately a new scan
-		 * the sampling rate is set by the coversion rate
-		 */
-		flags = TRIG_FOLLOW;
-	} else {
-		/* start a new scan (output at once) with a timer */
-		flags = TRIG_TIMER;
-	}
-	err |= comedi_check_trigger_src(&cmd->scan_begin_src, flags);
-
+	/*
+	 * For now, always use "scan" timing with all channels updated at once
+	 * (cmd->scan_begin_src == TRIG_TIMER, cmd->convert_src == TRIG_NOW).
+	 *
+	 * In a future version, "convert" timing with channels updated
+	 * indivually may be supported in high speed mode
+	 * (cmd->scan_begin_src == TRIG_FOLLOW, cmd->convert_src == TRIG_TIMER).
+	 */
+	err |= comedi_check_trigger_src(&cmd->scan_begin_src, TRIG_TIMER);
 	err |= comedi_check_trigger_src(&cmd->convert_src, TRIG_NOW);
 	err |= comedi_check_trigger_src(&cmd->scan_end_src, TRIG_COUNT);
 	err |= comedi_check_trigger_src(&cmd->stop_src, TRIG_COUNT | TRIG_NONE);
@@ -885,17 +877,7 @@ static int usbduxsigma_ao_cmdtest(struct comedi_device *dev,
 
 	err |= comedi_check_trigger_arg_is(&cmd->start_arg, 0);
 
-	if (cmd->scan_begin_src == TRIG_FOLLOW)	/* internal trigger */
-		err |= comedi_check_trigger_arg_is(&cmd->scan_begin_arg, 0);
-
-	if (cmd->scan_begin_src == TRIG_TIMER) {
-		err |= comedi_check_trigger_arg_min(&cmd->scan_begin_arg,
-						    1000000);
-	}
-
-	/* not used now, is for later use */
-	if (cmd->convert_src == TRIG_TIMER)
-		err |= comedi_check_trigger_arg_min(&cmd->convert_arg, 125000);
+	err |= comedi_check_trigger_arg_min(&cmd->scan_begin_arg, 1000000);
 
 	err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg,
 					   cmd->chanlist_len);
@@ -920,19 +902,13 @@ static int usbduxsigma_ao_cmd(struct comedi_device *dev,
 
 	down(&devpriv->sem);
 
-	if (cmd->convert_src == TRIG_TIMER) {
-		/*
-		 * timing of the conversion itself: every 125 us
-		 * at high speed (not used yet)
-		 */
-		devpriv->ao_timer = cmd->convert_arg / 125000;
-	} else {
-		/*
-		 * timing of the scan: every 1ms
-		 * we get all channels at once
-		 */
-		devpriv->ao_timer = cmd->scan_begin_arg / 1000000;
-	}
+	/*
+	 * For now, only "scan" timing is supported.  A future version may
+	 * support "convert" timing in high speed mode.
+	 *
+	 * Timing of the scan: every 1ms all channels updated at once.
+	 */
+	devpriv->ao_timer = cmd->scan_begin_arg / 1000000;
 
 	devpriv->ao_counter = devpriv->ao_timer;