[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, 2 insertions, 0 deletions

diff --git a/include/media/v4l2-device.h b/include/media/v4l2-device.h
index 6648036b728d..b16f307d471a 100644
--- a/include/media/v4l2-device.h
+++ b/include/media/v4l2-device.h
@@ -51,6 +51,8 @@ struct v4l2_device {
                         unsigned int notification, void *arg);
         /* The control handler. May be NULL. */
         struct v4l2_ctrl_handler *ctrl_handler;
+        /* BKL replacement mutex. Temporary solution only. */
+        struct mutex ioctl_lock;
 };
 
 /* Initialize v4l2_dev and make dev->driver_data point to v4l2_dev.