For V4L2 drivers:
-.. code-block:: none
+.. code-block:: c
struct foo_dev {
...
For sub-device drivers:
-.. code-block:: none
+.. code-block:: c
struct foo_dev {
...
1.2) Initialize the handler:
-.. code-block:: none
+.. code-block:: c
v4l2_ctrl_handler_init(&foo->ctrl_handler, nr_of_controls);
For V4L2 drivers:
-.. code-block:: none
+.. code-block:: c
foo->v4l2_dev.ctrl_handler = &foo->ctrl_handler;
For sub-device drivers:
-.. code-block:: none
+.. code-block:: c
foo->sd.ctrl_handler = &foo->ctrl_handler;
1.4) Clean up the handler at the end:
-.. code-block:: none
+.. code-block:: c
v4l2_ctrl_handler_free(&foo->ctrl_handler);
You add non-menu controls by calling :c:func:`v4l2_ctrl_new_std`:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl *v4l2_ctrl_new_std(struct v4l2_ctrl_handler *hdl,
const struct v4l2_ctrl_ops *ops,
Menu and integer menu controls are added by calling
:c:func:`v4l2_ctrl_new_std_menu`:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl *v4l2_ctrl_new_std_menu(struct v4l2_ctrl_handler *hdl,
const struct v4l2_ctrl_ops *ops,
Menu controls with a driver specific menu are added by calling
:c:func:`v4l2_ctrl_new_std_menu_items`:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl *v4l2_ctrl_new_std_menu_items(
struct v4l2_ctrl_handler *hdl,
Integer menu controls with a driver specific menu can be added by calling
:c:func:`v4l2_ctrl_new_int_menu`:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl *v4l2_ctrl_new_int_menu(struct v4l2_ctrl_handler *hdl,
const struct v4l2_ctrl_ops *ops,
These functions are typically called right after the
:c:func:`v4l2_ctrl_handler_init`:
-.. code-block:: none
+.. code-block:: c
static const s64 exp_bias_qmenu[] = {
-2, -1, 0, 1, 2
3) Optionally force initial control setup:
-.. code-block:: none
+.. code-block:: c
v4l2_ctrl_handler_setup(&foo->ctrl_handler);
4) Finally: implement the :c:type:`v4l2_ctrl_ops`
-.. code-block:: none
+.. code-block:: c
static const struct v4l2_ctrl_ops foo_ctrl_ops = {
.s_ctrl = foo_s_ctrl,
Usually all you need is s_ctrl:
-.. code-block:: none
+.. code-block:: c
static int foo_s_ctrl(struct v4l2_ctrl *ctrl)
{
The following union is used inside the control framework to access control
values:
-.. code-block:: none
+.. code-block:: c
union v4l2_ctrl_ptr {
s32 *p_s32;
The v4l2_ctrl struct contains these fields that can be used to access both
current and new values:
-.. code-block:: none
+.. code-block:: c
s32 val;
struct {
If the control has a simple s32 type type, then:
-.. code-block:: none
+.. code-block:: c
&ctrl->val == ctrl->p_new.p_s32
&ctrl->cur.val == ctrl->p_cur.p_s32
strength read-out that changes continuously. In that case you will need to
implement g_volatile_ctrl like this:
-.. code-block:: none
+.. code-block:: c
static int foo_g_volatile_ctrl(struct v4l2_ctrl *ctrl)
{
To mark a control as volatile you have to set V4L2_CTRL_FLAG_VOLATILE:
-.. code-block:: none
+.. code-block:: c
ctrl = v4l2_ctrl_new_std(&sd->ctrl_handler, ...);
if (ctrl)
Outside of the control ops you have to go through to helper functions to get
or set a single control value safely in your driver:
-.. code-block:: none
+.. code-block:: c
s32 v4l2_ctrl_g_ctrl(struct v4l2_ctrl *ctrl);
int v4l2_ctrl_s_ctrl(struct v4l2_ctrl *ctrl, s32 val);
You can also take the handler lock yourself:
-.. code-block:: none
+.. code-block:: c
mutex_lock(&state->ctrl_handler.lock);
pr_info("String value is '%s'\n", ctrl1->p_cur.p_char);
The v4l2_ctrl struct contains this union:
-.. code-block:: none
+.. code-block:: c
union {
u32 step;
Driver specific controls can be created using v4l2_ctrl_new_custom():
-.. code-block:: none
+.. code-block:: c
static const struct v4l2_ctrl_config ctrl_filter = {
.ops = &ctrl_custom_ops,
complex scenarios you can get dependencies from one control to another.
In that case you need to 'cluster' them:
-.. code-block:: none
+.. code-block:: c
struct foo {
struct v4l2_ctrl_handler ctrl_handler;
So when s_ctrl is called with V4L2_CID_AUDIO_VOLUME as argument, you should set
all two controls belonging to the audio_cluster:
-.. code-block:: none
+.. code-block:: c
static int foo_s_ctrl(struct v4l2_ctrl *ctrl)
{
In the example above the following are equivalent for the VOLUME case:
-.. code-block:: none
+.. code-block:: c
ctrl == ctrl->cluster[AUDIO_CL_VOLUME] == state->audio_cluster[AUDIO_CL_VOLUME]
ctrl->cluster[AUDIO_CL_MUTE] == state->audio_cluster[AUDIO_CL_MUTE]
In practice using cluster arrays like this becomes very tiresome. So instead
the following equivalent method is used:
-.. code-block:: none
+.. code-block:: c
struct {
/* audio cluster */
but it serves no other purpose. The effect is the same as creating an
array with two control pointers. So you can just do:
-.. code-block:: none
+.. code-block:: c
state->volume = v4l2_ctrl_new_std(&state->ctrl_handler, ...);
state->mute = v4l2_ctrl_new_std(&state->ctrl_handler, ...);
In order to simplify this a special variation of v4l2_ctrl_cluster was
introduced:
-.. code-block:: none
+.. code-block:: c
void v4l2_ctrl_auto_cluster(unsigned ncontrols, struct v4l2_ctrl **controls,
u8 manual_val, bool set_volatile);
the controls to the first handler, add the other controls to the second
handler and finally add the first handler to the second. For example:
-.. code-block:: none
+.. code-block:: c
v4l2_ctrl_new_std(&radio_ctrl_handler, &radio_ops, V4L2_CID_AUDIO_VOLUME, ...);
v4l2_ctrl_new_std(&radio_ctrl_handler, &radio_ops, V4L2_CID_AUDIO_MUTE, ...);
Or you can add specific controls to a handler:
-.. code-block:: none
+.. code-block:: c
volume = v4l2_ctrl_new_std(&video_ctrl_handler, &ops, V4L2_CID_AUDIO_VOLUME, ...);
v4l2_ctrl_new_std(&video_ctrl_handler, &ops, V4L2_CID_BRIGHTNESS, ...);
What you should not do is make two identical controls for two handlers.
For example:
-.. code-block:: none
+.. code-block:: c
v4l2_ctrl_new_std(&radio_ctrl_handler, &radio_ops, V4L2_CID_AUDIO_MUTE, ...);
v4l2_ctrl_new_std(&video_ctrl_handler, &video_ops, V4L2_CID_AUDIO_MUTE, ...);
You can do that by calling v4l2_ctrl_find:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl *volume;
Since v4l2_ctrl_find will lock the handler you have to be careful where you
use it. For example, this is not a good idea:
-.. code-block:: none
+.. code-block:: c
struct v4l2_ctrl_handler ctrl_handler;
...and in video_ops.s_ctrl:
-.. code-block:: none
+.. code-block:: c
case V4L2_CID_BRIGHTNESS:
contrast = v4l2_find_ctrl(&ctrl_handler, V4L2_CID_CONTRAST);
those low-level controls local to the subdev. You can do this by simply
setting the 'is_private' flag of the control to 1:
-.. code-block:: none
+.. code-block:: c
static const struct v4l2_ctrl_config ctrl_private = {
.ops = &ctrl_custom_ops,
from a sub-device driver changes. You can set a notify callback by calling
this function:
-.. code-block:: none
+.. code-block:: c
void v4l2_ctrl_notify(struct v4l2_ctrl *ctrl,
void (*notify)(struct v4l2_ctrl *ctrl, void *priv), void *priv);
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