staging: comedi: usbduxsigma: 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: NH Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxsigma.c

@@ -164,8 +164,6 @@ struct usbduxsigma_private {
 	unsigned ao_cmd_running:1;
 	unsigned 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;
@@ -226,14 +224,6 @@ static void usbduxsigma_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 state of the dio pins to allow external trigger */
 		dio_state = be32_to_cpu(devpriv->in_buf[0]);
 
@@ -247,6 +237,10 @@ static void usbduxsigma_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 */
@@ -578,14 +572,6 @@ static int usbduxsigma_ai_cmdtest(struct comedi_device *dev,
 	if (devpriv->ai_timer < 1)
 		err |= -EINVAL;
 
-	if (cmd->stop_src == TRIG_COUNT) {
-		/* data arrives as one packet */
-		devpriv->ai_sample_count = cmd->stop_arg;
-	} else {
-		/* continuous acquisition */
-		devpriv->ai_sample_count = 0;
-	}
-
 	if (err)
 		return 4;