Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild

[mirror_ubuntu-bionic-kernel.git] / Documentation / video4linux / v4l2-controls.txt

diff --git a/Documentation/video4linux/v4l2-controls.txt b/Documentation/video4linux/v4l2-controls.txt
index cfe52c798d743b0979a31c414948a5c72c491e46..676f87366025a57a7158b2e04de9605883a5a124 100644 (file)
--- a/Documentation/video4linux/v4l2-controls.txt
+++ b/Documentation/video4linux/v4l2-controls.txt
@@ -715,14 +715,20 @@ a control of this type whenever the first control belonging to a new control
 class is added.
 
 
-Proposals for Extensions
-========================
+Adding Notify Callbacks
+=======================
+
+Sometimes the platform or bridge driver needs to be notified when a control
+from a sub-device driver changes. You can set a notify callback by calling
+this function:
 
-Some ideas for future extensions to the spec:
+void v4l2_ctrl_notify(struct v4l2_ctrl *ctrl,
+       void (*notify)(struct v4l2_ctrl *ctrl, void *priv), void *priv);
 
-1) Add a V4L2_CTRL_FLAG_HEX to have values shown as hexadecimal instead of
-decimal. Useful for e.g. video_mute_yuv.
+Whenever the give control changes value the notify callback will be called
+with a pointer to the control and the priv pointer that was passed with
+v4l2_ctrl_notify. Note that the control's handler lock is held when the
+notify function is called.
 
-2) It is possible to mark in the controls array which controls have been
-successfully written and which failed by for example adding a bit to the
-control ID. Not sure if it is worth the effort, though.
+There can be only one notify function per control handler. Any attempt
+to set another notify function will cause a WARN_ON.