[media] V4L: improve the BKL replacement heuristic

The BKL replacement mutex had some serious performance side-effects on
V4L drivers. It is replaced by a better heuristic that works around the
worst of the side-effects.

Read the v4l2-dev.c comments for the whole sorry story. This is a
temporary measure only until we can convert all v4l drivers to use
unlocked_ioctl.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/media/video/v4l2-device.c b/drivers/media/video/v4l2-device.c
index 0b08f96b74a5..7fe6f92af480 100644
--- a/drivers/media/video/v4l2-device.c
+++ b/drivers/media/video/v4l2-device.c
@@ -35,6 +35,7 @@ int v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev)
 
         INIT_LIST_HEAD(&v4l2_dev->subdevs);
         spin_lock_init(&v4l2_dev->lock);
+        mutex_init(&v4l2_dev->ioctl_lock);
         v4l2_dev->dev = dev;
         if (dev == NULL) {
                 /* If dev == NULL, then name must be filled in by the caller */