staging: comedi: usbdux: tidy up usbdux_ao_cmd()

Rename the local variable used for the private data pointer to the
comedi "norm".

Remove the unnecessary sanity check of the private data pointer. This
function can only be called is the private data was allocated during
the attach.

Make sure an ao command is not already running and return -EBUSY.

Tidy up the exit path using goto to ensure that the semaphore is
released.

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/usbdux.c

@@ -1188,72 +1188,74 @@ static int usbdux_ao_cmdtest(struct comedi_device *dev,
 
 static int usbdux_ao_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 {
+	struct usbdux_private *devpriv = dev->private;
 	struct comedi_cmd *cmd = &s->async->cmd;
-	unsigned int chan, gain;
-	int i, ret;
-	struct usbdux_private *this_usbduxsub = dev->private;
+	int ret = -EBUSY;
+	int i;
 
-	if (!this_usbduxsub)
-		return -EFAULT;
+	down(&devpriv->sem);
 
-	down(&this_usbduxsub->sem);
+	if (devpriv->ao_cmd_running)
+		goto ao_cmd_exit;
 
 	/* set current channel of the running acquisition to zero */
 	s->async->cur_chan = 0;
+
 	for (i = 0; i < cmd->chanlist_len; ++i) {
-		chan = CR_CHAN(cmd->chanlist[i]);
-		gain = CR_RANGE(cmd->chanlist[i]);
+		unsigned int chan = CR_CHAN(cmd->chanlist[i]);
+
 		if (i >= NUMOUTCHANNELS)
 			break;
-		this_usbduxsub->dac_commands[i] = (chan << 6);
+
+		devpriv->dac_commands[i] = chan << 6;
 	}
 
 	/* we count in steps of 1ms (125us) */
 	/* 125us mode not used yet */
-	if (0) {		/* (this_usbduxsub->high_speed) */
+	if (0) {		/* (devpriv->high_speed) */
 		/* 125us */
 		/* timing of the conversion itself: every 125 us */
-		this_usbduxsub->ao_timer = cmd->convert_arg / 125000;
+		devpriv->ao_timer = cmd->convert_arg / 125000;
 	} else {
 		/* 1ms */
 		/* timing of the scan: we get all channels at once */
-		this_usbduxsub->ao_timer = cmd->scan_begin_arg / 1000000;
-		if (this_usbduxsub->ao_timer < 1) {
-			up(&this_usbduxsub->sem);
-			return -EINVAL;
+		devpriv->ao_timer = cmd->scan_begin_arg / 1000000;
+		if (devpriv->ao_timer < 1) {
+			ret = -EINVAL;
+			goto ao_cmd_exit;
 		}
 	}
-	this_usbduxsub->ao_counter = this_usbduxsub->ao_timer;
+
+	devpriv->ao_counter = devpriv->ao_timer;
 
 	if (cmd->stop_src == TRIG_COUNT) {
 		/* not continuous */
 		/* counter */
 		/* high speed also scans everything at once */
-		if (0) {	/* (this_usbduxsub->high_speed) */
-			this_usbduxsub->ao_sample_count =
-			    (cmd->stop_arg) * (cmd->scan_end_arg);
+		if (0) {	/* (devpriv->high_speed) */
+			devpriv->ao_sample_count = cmd->stop_arg *
+						   cmd->scan_end_arg;
 		} else {
 			/* there's no scan as the scan has been */
 			/* perf inside the FX2 */
 			/* data arrives as one packet */
-			this_usbduxsub->ao_sample_count = cmd->stop_arg;
+			devpriv->ao_sample_count = cmd->stop_arg;
 		}
-		this_usbduxsub->ao_continous = 0;
+		devpriv->ao_continous = 0;
 	} else {
 		/* continous acquisition */
-		this_usbduxsub->ao_continous = 1;
-		this_usbduxsub->ao_sample_count = 0;
+		devpriv->ao_continous = 1;
+		devpriv->ao_sample_count = 0;
 	}
 
 	if (cmd->start_src == TRIG_NOW) {
 		/* enable this acquisition operation */
-		this_usbduxsub->ao_cmd_running = 1;
+		devpriv->ao_cmd_running = 1;
 		ret = usbduxsub_submit_outurbs(dev);
 		if (ret < 0) {
-			this_usbduxsub->ao_cmd_running = 0;
+			devpriv->ao_cmd_running = 0;
 			/* fixme: unlink here?? */
-			up(&this_usbduxsub->sem);
-			return ret;
+			goto ao_cmd_exit;
 		}
 		s->async->inttrig = NULL;
 	} else {
@@ -1263,8 +1265,10 @@ static int usbdux_ao_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 		s->async->inttrig = usbdux_ao_inttrig;
 	}
 
-	up(&this_usbduxsub->sem);
-	return 0;
+ao_cmd_exit:
+	up(&devpriv->sem);
+
+	return ret;
 }
 
 static int usbdux_dio_insn_config(struct comedi_device *dev,