media: s2255: Use refcount_t instead of atomic_t for num_channels

Use an API that resembles more the actual use of num_channels.

Found by cocci:
drivers/media/usb/s2255/s2255drv.c:2362:5-24: WARNING: atomic_dec_and_test variation before object free at line 2363.
drivers/media/usb/s2255/s2255drv.c:1557:5-24: WARNING: atomic_dec_and_test variation before object free at line 1558.

Link: https://lore.kernel.org/linux-media/20240429-fix-cocci-v3-11-3c4865f5a4b0@chromium.org
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Author: ribalda

drivers/media/usb/s2255/s2255drv.c

@@ -247,7 +247,7 @@ struct s2255_vc {
 struct s2255_dev {
 	struct s2255_vc         vc[MAX_CHANNELS];
 	struct v4l2_device      v4l2_dev;
-	atomic_t                num_channels;
+	refcount_t		num_channels;
 	int			frames;
 	struct mutex		lock;	/* channels[].vdev.lock */
 	struct mutex		cmdlock; /* protects cmdbuf */
@@ -1550,11 +1550,11 @@ static void s2255_video_device_release(struct video_device *vdev)
 		container_of(vdev, struct s2255_vc, vdev);
 
 	dprintk(dev, 4, "%s, chnls: %d\n", __func__,
-		atomic_read(&dev->num_channels));
+		refcount_read(&dev->num_channels));
 
 	v4l2_ctrl_handler_free(&vc->hdl);
 
-	if (atomic_dec_and_test(&dev->num_channels))
+	if (refcount_dec_and_test(&dev->num_channels))
 		s2255_destroy(dev);
 	return;
 }
@@ -1659,19 +1659,19 @@ static int s2255_probe_v4l(struct s2255_dev *dev)
 				"failed to register video device!\n");
 			break;
 		}
-		atomic_inc(&dev->num_channels);
+		refcount_inc(&dev->num_channels);
 		v4l2_info(&dev->v4l2_dev, "V4L2 device registered as %s\n",
 			  video_device_node_name(&vc->vdev));
 
 	}
 	pr_info("Sensoray 2255 V4L driver Revision: %s\n",
 		S2255_VERSION);
 	/* if no channels registered, return error and probe will fail*/
-	if (atomic_read(&dev->num_channels) == 0) {
+	if (refcount_read(&dev->num_channels) == 0) {
 		v4l2_device_unregister(&dev->v4l2_dev);
 		return ret;
 	}
-	if (atomic_read(&dev->num_channels) != MAX_CHANNELS)
+	if (refcount_read(&dev->num_channels) != MAX_CHANNELS)
 		pr_warn("s2255: Not all channels available.\n");
 	return 0;
 }
@@ -2221,7 +2221,7 @@ static int s2255_probe(struct usb_interface *interface,
 		goto errorFWDATA1;
 	}
 
-	atomic_set(&dev->num_channels, 0);
+	refcount_set(&dev->num_channels, 0);
 	dev->pid = id->idProduct;
 	dev->fw_data = kzalloc(sizeof(struct s2255_fw), GFP_KERNEL);
 	if (!dev->fw_data)
@@ -2341,12 +2341,12 @@ static void s2255_disconnect(struct usb_interface *interface)
 {
 	struct s2255_dev *dev = to_s2255_dev(usb_get_intfdata(interface));
 	int i;
-	int channels = atomic_read(&dev->num_channels);
+	int channels = refcount_read(&dev->num_channels);
 	mutex_lock(&dev->lock);
 	v4l2_device_disconnect(&dev->v4l2_dev);
 	mutex_unlock(&dev->lock);
 	/*see comments in the uvc_driver.c usb disconnect function */
-	atomic_inc(&dev->num_channels);
+	refcount_inc(&dev->num_channels);
 	/* unregister each video device. */
 	for (i = 0; i < channels; i++)
 		video_unregister_device(&dev->vc[i].vdev);
@@ -2359,7 +2359,7 @@ static void s2255_disconnect(struct usb_interface *interface)
 		dev->vc[i].vidstatus_ready = 1;
 		wake_up(&dev->vc[i].wait_vidstatus);
 	}
-	if (atomic_dec_and_test(&dev->num_channels))
+	if (refcount_dec_and_test(&dev->num_channels))
 		s2255_destroy(dev);
 	dev_info(&interface->dev, "%s\n", __func__);
 }