staging: comedi: introduce comedi_buf_n_bytes_ready()

Introduce an inline helper to return the number of bytes that are
ready to read from the comedi_async buffer. Use the helper in the
comedi drivers that currently do the calculation as part of the
(*poll) operation.

Also, use the helper in comedi_fops where the calculation is used as
part of the subdevice going nonbusy.

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/comedi_fops.c

@@ -997,7 +997,7 @@ static int do_bufinfo_ioctl(struct comedi_device *dev,
 		comedi_buf_read_free(s, bi.bytes_read);
 
 		if (comedi_is_subdevice_idle(s) &&
-		    async->buf_write_count == async->buf_read_count) {
+		    comedi_buf_n_bytes_ready(s) == 0) {
 			do_become_nonbusy(dev, s);
 		}
 	}
@@ -2303,8 +2303,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 		new_s = comedi_read_subdevice(dev, minor);
 		if (dev->attached && old_detach_count == dev->detach_count &&
 		    s == new_s && new_s->async == async) {
-			if (become_nonbusy ||
-			    async->buf_read_count - async->buf_write_count == 0)
+			if (become_nonbusy || comedi_buf_n_bytes_ready(s) == 0)
 				do_become_nonbusy(dev, s);
 		}
 		mutex_unlock(&dev->mutex);

drivers/staging/comedi/comedidev.h

@@ -400,6 +400,11 @@ static inline unsigned int bytes_per_sample(const struct comedi_subdevice *subd)
  */
 int comedi_set_hw_dev(struct comedi_device *dev, struct device *hw_dev);
 
+static inline unsigned int comedi_buf_n_bytes_ready(struct comedi_subdevice *s)
+{
+	return s->async->buf_write_count - s->async->buf_read_count;
+}
+
 unsigned int comedi_buf_write_alloc(struct comedi_subdevice *s, unsigned int n);
 unsigned int comedi_buf_write_free(struct comedi_subdevice *s, unsigned int n);
 

drivers/staging/comedi/drivers/das16m1.c

@@ -477,7 +477,7 @@ static int das16m1_poll(struct comedi_device *dev, struct comedi_subdevice *s)
 	das16m1_handler(dev, status);
 	spin_unlock_irqrestore(&dev->spinlock, flags);
 
-	return s->async->buf_write_count - s->async->buf_read_count;
+	return comedi_buf_n_bytes_ready(s);
 }
 
 static irqreturn_t das16m1_interrupt(int irq, void *d)

drivers/staging/comedi/drivers/das1800.c

@@ -696,7 +696,7 @@ static int das1800_ai_poll(struct comedi_device *dev,
 	das1800_ai_handler(dev);
 	spin_unlock_irqrestore(&dev->spinlock, flags);
 
-	return s->async->buf_write_count - s->async->buf_read_count;
+	return comedi_buf_n_bytes_ready(s);
 }
 
 static irqreturn_t das1800_interrupt(int irq, void *d)

drivers/staging/comedi/drivers/ni_mio_common.c

@@ -1878,7 +1878,7 @@ static int ni_ai_poll(struct comedi_device *dev, struct comedi_subdevice *s)
 #else
 	ni_sync_ai_dma(dev);
 #endif
-	count = s->async->buf_write_count - s->async->buf_read_count;
+	count = comedi_buf_n_bytes_ready(s);
 	spin_unlock_irqrestore(&dev->spinlock, flags);
 
 	return count;

drivers/staging/comedi/drivers/ni_pcidio.c

@@ -361,7 +361,7 @@ static int ni_pcidio_poll(struct comedi_device *dev, struct comedi_subdevice *s)
 	if (devpriv->di_mite_chan)
 		mite_sync_input_dma(devpriv->di_mite_chan, s);
 	spin_unlock(&devpriv->mite_channel_lock);
-	count = s->async->buf_write_count - s->async->buf_read_count;
+	count = comedi_buf_n_bytes_ready(s);
 	spin_unlock_irqrestore(&dev->spinlock, irq_flags);
 	return count;
 }

drivers/staging/comedi/drivers/pcl812.c

@@ -985,7 +985,7 @@ static int pcl812_ai_poll(struct comedi_device *dev, struct comedi_subdevice *s)
 
 	spin_unlock_irqrestore(&dev->spinlock, flags);
 
-	return s->async->buf_write_count - s->async->buf_read_count;
+	return comedi_buf_n_bytes_ready(s);
 }
 
 static int pcl812_ai_cancel(struct comedi_device *dev,

drivers/staging/comedi/drivers/pcl816.c

@@ -516,7 +516,7 @@ static int pcl816_ai_poll(struct comedi_device *dev, struct comedi_subdevice *s)
 
 	cfc_handle_events(dev, s);
 
-	return s->async->buf_write_count - s->async->buf_read_count;
+	return comedi_buf_n_bytes_ready(s);
 }
 
 static int pcl816_ai_cancel(struct comedi_device *dev,