[media] pwc: Allow dqbuf / read to complete while waiting for controls

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/pwc/pwc-if.c

@@ -1160,6 +1160,7 @@ static int usb_pwc_probe(struct usb_interface *intf, const struct usb_device_id
 	pwc_construct(pdev); /* set min/max sizes correct */
 
 	mutex_init(&pdev->modlock);
+	mutex_init(&pdev->udevlock);
 	spin_lock_init(&pdev->queued_bufs_lock);
 	INIT_LIST_HEAD(&pdev->queued_bufs);
 
@@ -1297,6 +1298,7 @@ static void usb_pwc_disconnect(struct usb_interface *intf)
 {
 	struct pwc_device *pdev  = usb_get_intfdata(intf);
 
+	mutex_lock(&pdev->udevlock);
 	mutex_lock(&pdev->modlock);
 
 	usb_set_intfdata(intf, NULL);
@@ -1306,6 +1308,7 @@ static void usb_pwc_disconnect(struct usb_interface *intf)
 	pdev->udev = NULL;
 
 	mutex_unlock(&pdev->modlock);
+	mutex_unlock(&pdev->udevlock);
 
 	pwc_remove_sysfs_files(pdev);
 	video_unregister_device(&pdev->vdev);

drivers/media/video/pwc/pwc-v4l.c

@@ -526,8 +526,24 @@ static int pwc_g_volatile_ctrl(struct v4l2_ctrl *ctrl)
 		container_of(ctrl->handler, struct pwc_device, ctrl_handler);
 	int ret = 0;
 
-	if (!pdev->udev)
-		return -ENODEV;
+	/*
+	 * Sometimes it can take quite long for the pwc to complete usb control
+	 * transfers, so release the modlock to give streaming by another
+	 * process / thread the chance to continue with a dqbuf.
+	 */
+	mutex_unlock(&pdev->modlock);
+
+	/*
+	 * Take the udev-lock to protect against the disconnect handler
+	 * completing and setting dev->udev to NULL underneath us. Other code
+	 * does not need to do this since it is protected by the modlock.
+	 */
+	mutex_lock(&pdev->udevlock);
+
+	if (!pdev->udev) {
+		ret = -ENODEV;
+		goto leave;
+	}
 
 	switch (ctrl->id) {
 	case V4L2_CID_AUTO_WHITE_BALANCE:
@@ -590,6 +606,9 @@ static int pwc_g_volatile_ctrl(struct v4l2_ctrl *ctrl)
 	if (ret)
 		PWC_ERROR("g_ctrl %s error %d\n", ctrl->name, ret);
 
+leave:
+	mutex_unlock(&pdev->udevlock);
+	mutex_lock(&pdev->modlock);
 	return ret;
 }
 
@@ -751,8 +770,14 @@ static int pwc_s_ctrl(struct v4l2_ctrl *ctrl)
 		container_of(ctrl->handler, struct pwc_device, ctrl_handler);
 	int ret = 0;
 
-	if (!pdev->udev)
-		return -ENODEV;
+	/* See the comments on locking in pwc_g_volatile_ctrl */
+	mutex_unlock(&pdev->modlock);
+	mutex_lock(&pdev->udevlock);
+
+	if (!pdev->udev) {
+		ret = -ENODEV;
+		goto leave;
+	}
 
 	switch (ctrl->id) {
 	case V4L2_CID_BRIGHTNESS:
@@ -841,6 +866,9 @@ static int pwc_s_ctrl(struct v4l2_ctrl *ctrl)
 	if (ret)
 		PWC_ERROR("s_ctrl %s error %d\n", ctrl->name, ret);
 
+leave:
+	mutex_unlock(&pdev->udevlock);
+	mutex_lock(&pdev->modlock);
 	return ret;
 }
 

drivers/media/video/pwc/pwc.h

@@ -200,6 +200,9 @@ struct pwc_device
 
 	/* Pointer to our usb_device, may be NULL after unplug */
 	struct usb_device *udev;
+	/* Protects the setting of udev to NULL by our disconnect handler */
+	struct mutex udevlock;
+
 	/* type of cam (645, 646, 675, 680, 690, 720, 730, 740, 750) */
 	int type;
 	int release;		/* release number */