[media] v4l2-ctrl: Add helper function for the controls range update

This patch adds a helper function that allows to modify range,
i.e. minimum, maximum, step and default value of a v4l2 control,
after the control has been created and initialized. This is helpful
in situations when range of a control depends on user configurable
parameters, e.g. camera sensor absolute exposure time depending on
an output image resolution and frame rate.
v4l2_ctrl_modify_range() function allows to modify range of an
INTEGER, BOOL, MENU, INTEGER_MENU and BITMASK type controls.
Based on a patch from Hans Verkuil http://patchwork.linuxtv.org/patch/8654.

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
index c4cc04136074..91125b6f05a5 100644
--- a/include/media/v4l2-ctrls.h
+++ b/include/media/v4l2-ctrls.h
@@ -518,6 +518,26 @@ void v4l2_ctrl_activate(struct v4l2_ctrl *ctrl, bool active);
   */
 void v4l2_ctrl_grab(struct v4l2_ctrl *ctrl, bool grabbed);
 
+/** v4l2_ctrl_modify_range() - Update the range of a control.
+  * @ctrl:      The control to update.
+  * @min:       The control's minimum value.
+  * @max:       The control's maximum value.
+  * @step:      The control's step value
+  * @def:       The control's default value.
+  *
+  * Update the range of a control on the fly. This works for control types
+  * INTEGER, BOOLEAN, MENU, INTEGER MENU and BITMASK. For menu controls the
+  * @step value is interpreted as a menu_skip_mask.
+  *
+  * An error is returned if one of the range arguments is invalid for this
+  * control type.
+  *
+  * This function assumes that the control handler is not locked and will
+  * take the lock itself.
+  */
+int v4l2_ctrl_modify_range(struct v4l2_ctrl *ctrl,
+                        s32 min, s32 max, u32 step, s32 def);
+
 /** v4l2_ctrl_lock() - Helper function to lock the handler
   * associated with the control.
   * @ctrl:      The control to lock.
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 94cbe26e9f00..928799c2e2d9 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -1822,6 +1822,7 @@ struct v4l2_event_vsync {
 /* Payload for V4L2_EVENT_CTRL */
 #define V4L2_EVENT_CTRL_CH_VALUE                (1 << 0)
 #define V4L2_EVENT_CTRL_CH_FLAGS                (1 << 1)
+#define V4L2_EVENT_CTRL_CH_RANGE                (1 << 2)
 
 struct v4l2_event_ctrl {
         __u32 changes;