staging: comedi: usbdux: use comedi_async 'scans_done' to detect AI EOA

Remove the private data member 'ai_sample_count' and use the comedi_async
'scans_done' member to detect the analog input end-of-acquisition.

Move the EOA check so it happens after adding the samples from the current
urb to the async buffer. This prevents the unnecessary resubmit of the urb
when the EOA occurs.
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

@@ -202,8 +202,6 @@ struct usbdux_private {
 	unsigned int ao_cmd_running:1;
 	unsigned int pwm_cmd_running:1;
 
-	/* number of samples to acquire */
-	int ai_sample_count;
 	/* time between samples in units of the timer */
 	unsigned int ai_timer;
 	unsigned int ao_timer;
@@ -263,14 +261,6 @@ static void usbduxsub_ai_handle_urb(struct comedi_device *dev,
 	if (devpriv->ai_counter == 0) {
 		devpriv->ai_counter = devpriv->ai_timer;
 
-		if (cmd->stop_src == TRIG_COUNT) {
-			devpriv->ai_sample_count--;
-			if (devpriv->ai_sample_count < 0) {
-				async->events |= COMEDI_CB_EOA;
-				return;
-			}
-		}
-
 		/* get the data from the USB bus and hand it over to comedi */
 		for (i = 0; i < cmd->chanlist_len; i++) {
 			unsigned int range = CR_RANGE(cmd->chanlist[i]);
@@ -284,6 +274,10 @@ static void usbduxsub_ai_handle_urb(struct comedi_device *dev,
 			if (!comedi_buf_write_samples(s, &val, 1))
 				return;
 		}
+
+		if (cmd->stop_src == TRIG_COUNT &&
+		    async->scans_done >= cmd->stop_arg)
+			async->events |= COMEDI_CB_EOA;
 	}
 
 	/* if command is still running, resubmit urb */
@@ -732,14 +726,6 @@ static int usbdux_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 
 	devpriv->ai_counter = devpriv->ai_timer;
 
-	if (cmd->stop_src == TRIG_COUNT) {
-		/* data arrives as one packet */
-		devpriv->ai_sample_count = cmd->stop_arg;
-	} else {
-		/* continous acquisition */
-		devpriv->ai_sample_count = 0;
-	}
-
 	if (cmd->start_src == TRIG_NOW) {
 		/* enable this acquisition operation */
 		devpriv->ai_cmd_running = 1;