Re: [PATCH v14 06/11] v4l2-ctrls: add support for V4L2_CTRL_WHICH_MIN/MAX_VAL

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Yunke and Hans,

Thank you for the patch.

On Fri, Dec 01, 2023 at 04:18:57PM +0900, Yunke Cao wrote:
> From: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> 
> Add the capability of retrieving the min and max values of a
> compound control.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Signed-off-by: Yunke Cao <yunkec@google.com>
> ---
> Changelog since v13:
> - Updated comments of v4l2_ctrl_new_std_compound()
> Changelog since v12:
> - Addressed comments from Hans.
> Changelog since v11:
> - Added a flag V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX.
> - Modified std_min/max_compound() to be void function. Moved the check of
>   whether WHICH_MIN/MAX_VAL into prepare_ext_ctrls(), and return EINVAL.
> - Modified documentations to reflect this change.
> Changelog since v10:
> - No change.
> Changelog since v9:
> - No change.
> Changelog since v8:
> - Return ENODATA when min/max is not implemented. Document this behavior.
> - Created a shared helper function __v4l2_ctrl_type_op_init that takes "which"
>   as a parameter. Call it in def, min and max operations.
> Changelog since v7:
> - Document that the definition of the min/max are provided by compound controls
>   are defined in control documentation.
> - Return error, instead of zeroed memory for v4l2_ctrl_ptr_create(NULL).
> 
>  .../media/v4l/vidioc-g-ext-ctrls.rst          |  22 ++-
>  .../media/v4l/vidioc-queryctrl.rst            |   9 +-
>  .../media/videodev2.h.rst.exceptions          |   3 +
>  drivers/media/i2c/imx214.c                    |   5 +-
>  .../media/platform/qcom/venus/venc_ctrls.c    |   9 +-
>  drivers/media/v4l2-core/v4l2-ctrls-api.c      |  54 +++++--
>  drivers/media/v4l2-core/v4l2-ctrls-core.c     | 151 +++++++++++++++---
>  drivers/media/v4l2-core/v4l2-ioctl.c          |   4 +-
>  include/media/v4l2-ctrls.h                    |  36 ++++-
>  include/uapi/linux/videodev2.h                |   3 +
>  10 files changed, 248 insertions(+), 48 deletions(-)

I'm wondering, would it make sense to include in this series, before
this patch, the following (or a similar) change ?

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index f4988f03640a..52208f2d71f3 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -1094,7 +1094,8 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 	if (ret < 0)
 		return ret;

-	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL) {
+	switch (ctrls->which) {
+	case V4L2_CTRL_WHICH_DEF_VAL:
 		for (i = 0; i < ctrls->count; ++ctrl, ++i) {
 			struct v4l2_queryctrl qc = { .id = ctrl->id };

@@ -1108,24 +1109,28 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 		}

 		return 0;
-	}

-	ret = uvc_ctrl_begin(chain);
-	if (ret < 0)
-		return ret;
-
-	for (i = 0; i < ctrls->count; ++ctrl, ++i) {
-		ret = uvc_ctrl_get(chain, ctrl);
-		if (ret < 0) {
-			uvc_ctrl_rollback(handle);
-			ctrls->error_idx = i;
+	case V4L2_CTRL_WHICH_CUR_VAL:
+		ret = uvc_ctrl_begin(chain);
+		if (ret < 0)
 			return ret;
+
+		for (i = 0; i < ctrls->count; ++ctrl, ++i) {
+			ret = uvc_ctrl_get(chain, ctrl);
+			if (ret < 0) {
+				uvc_ctrl_rollback(handle);
+				ctrls->error_idx = i;
+				return ret;
+			}
 		}
+
+		ctrls->error_idx = 0;
+
+		return uvc_ctrl_rollback(handle);
+
+	default:
+		return -EINVAL;
 	}
-
-	ctrls->error_idx = 0;
-
-	return uvc_ctrl_rollback(handle);
 }

 static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh *handle,

> diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> index 7b1001d11f9c..0b87c23e66ff 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> @@ -330,14 +330,26 @@ still cause this situation.
>        - Which value of the control to get/set/try.
>      * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
>  	the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
> -	value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
> -	these controls have to be retrieved from a request or tried/set for
> -	a request. In the latter case the ``request_fd`` field contains the
> +	value of the control, ``V4L2_CTRL_WHICH_MIN_VAL`` will return the minimum
> +	value of the control, and ``V4L2_CTRL_WHICH_MAX_VAL`` will return the maximum
> +	value of the control. ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
> +	the control value has to be retrieved from a request or tried/set for
> +	a request. In that case the ``request_fd`` field contains the
>  	file descriptor of the request that should be used. If the device
>  	does not support requests, then ``EACCES`` will be returned.
>  
> -	When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
> -	get the default value of the control, you cannot set or try it.
> +	When using ``V4L2_CTRL_WHICH_DEF_VAL``, ``V4L2_CTRL_WHICH_MIN_VAL``
> +	or ``V4L2_CTRL_WHICH_MAX_VAL`` be aware that you can only get the
> +	default/minimum/maximum value of the control, you cannot set or try it.
> +
> +	Whether a control supports querying the minimum and maximum values using
> +	``V4L2_CTRL_WHICH_MIN_VAL`` and ``V4L2_CTRL_WHICH_MAX_VAL`` is indicated
> +	by the ``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX`` flag. Most non-compound
> +	control types support this. For controls with compound types, the
> +	definition of minimum/maximum values are provided by
> +	the control documentation. If a compound control does not document the
> +	meaning of minimum/maximum value, then querying the minimum or maximum
> +	value will result in the error code -EINVAL.
>  
>  	For backwards compatibility you can also use a control class here
>  	(see :ref:`ctrl-class`). In that case all controls have to
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> index 56d5c8b0b88b..b39f7e27bbbe 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
> @@ -447,7 +447,10 @@ See also the examples in :ref:`control`.
>        - n/a
>        - A struct :c:type:`v4l2_rect`, containing a rectangle described by
>  	the position of its top-left corner, the width and the height. Units
> -	depend on the use case.
> +	depend on the use case. Support for ``V4L2_CTRL_WHICH_MIN_VAL`` and
> +	``V4L2_CTRL_WHICH_MAX_VAL`` is optional and depends on the
> +	``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX`` flag. See the documentation of
> +	the specific control on how to interpret the minimum and maximum values.
>      * - ``V4L2_CTRL_TYPE_H264_SPS``
>        - n/a
>        - n/a
> @@ -664,6 +667,10 @@ See also the examples in :ref:`control`.
>  	``dims[0]``. So setting the control with a differently sized
>  	array will change the ``elems`` field when the control is
>  	queried afterwards.
> +    * - ``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX``
> +      - 0x1000
> +      - This control supports getting minimum and maximum values using
> +      vidioc_g_ext_ctrls with V4L2_CTRL_WHICH_MIN/MAX_VAL.
>  
>  Return Value
>  ============
> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> index c46082ef0e4d..a417af25e9a4 100644
> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> @@ -393,6 +393,7 @@ replace define V4L2_CTRL_FLAG_HAS_PAYLOAD control-flags
>  replace define V4L2_CTRL_FLAG_EXECUTE_ON_WRITE control-flags
>  replace define V4L2_CTRL_FLAG_MODIFY_LAYOUT control-flags
>  replace define V4L2_CTRL_FLAG_DYNAMIC_ARRAY control-flags
> +replace define V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX control-flags
>  
>  replace define V4L2_CTRL_FLAG_NEXT_CTRL control
>  replace define V4L2_CTRL_FLAG_NEXT_COMPOUND control
> @@ -567,6 +568,8 @@ ignore define V4L2_CTRL_DRIVER_PRIV
>  ignore define V4L2_CTRL_MAX_DIMS
>  ignore define V4L2_CTRL_WHICH_CUR_VAL
>  ignore define V4L2_CTRL_WHICH_DEF_VAL
> +ignore define V4L2_CTRL_WHICH_MIN_VAL
> +ignore define V4L2_CTRL_WHICH_MAX_VAL
>  ignore define V4L2_CTRL_WHICH_REQUEST_VAL
>  ignore define V4L2_OUT_CAP_CUSTOM_TIMINGS
>  ignore define V4L2_CID_MAX_CTRLS
> diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
> index 4f77ea02cc27..926b5cae12d8 100644
> --- a/drivers/media/i2c/imx214.c
> +++ b/drivers/media/i2c/imx214.c
> @@ -998,7 +998,10 @@ static int imx214_probe(struct i2c_client *client)
>  	imx214->unit_size = v4l2_ctrl_new_std_compound(&imx214->ctrls,
>  				NULL,
>  				V4L2_CID_UNIT_CELL_SIZE,
> -				v4l2_ctrl_ptr_create((void *)&unit_size));
> +				v4l2_ctrl_ptr_create((void *)&unit_size),
> +				v4l2_ctrl_ptr_create(NULL),
> +				v4l2_ctrl_ptr_create(NULL));
> +
>  	ret = imx214->ctrls.error;
>  	if (ret) {
>  		dev_err(&client->dev, "%s control init failed (%d)\n",
> diff --git a/drivers/media/platform/qcom/venus/venc_ctrls.c b/drivers/media/platform/qcom/venus/venc_ctrls.c
> index d9d2a293f3ef..7f370438d655 100644
> --- a/drivers/media/platform/qcom/venus/venc_ctrls.c
> +++ b/drivers/media/platform/qcom/venus/venc_ctrls.c
> @@ -607,11 +607,16 @@ int venc_ctrl_init(struct venus_inst *inst)
>  
>  	v4l2_ctrl_new_std_compound(&inst->ctrl_handler, &venc_ctrl_ops,
>  				   V4L2_CID_COLORIMETRY_HDR10_CLL_INFO,
> -				   v4l2_ctrl_ptr_create(&p_hdr10_cll));
> +				   v4l2_ctrl_ptr_create(&p_hdr10_cll),
> +				   v4l2_ctrl_ptr_create(NULL),
> +				   v4l2_ctrl_ptr_create(NULL));
>  
>  	v4l2_ctrl_new_std_compound(&inst->ctrl_handler, &venc_ctrl_ops,
>  				   V4L2_CID_COLORIMETRY_HDR10_MASTERING_DISPLAY,
> -				   v4l2_ctrl_ptr_create((void *)&p_hdr10_mastering));
> +				   v4l2_ctrl_ptr_create((void *)&p_hdr10_mastering),
> +				   v4l2_ctrl_ptr_create(NULL),
> +				   v4l2_ctrl_ptr_create(NULL));
> +
>  
>  	v4l2_ctrl_new_std_menu(&inst->ctrl_handler, &venc_ctrl_ops,
>  			       V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD_TYPE,
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> index 002ea6588edf..d022e1ed4835 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> @@ -94,6 +94,22 @@ static int def_to_user(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
>  	return ptr_to_user(c, ctrl, ctrl->p_new);
>  }
>  
> +/* Helper function: copy the minimum control value back to the caller */
> +static int min_to_user(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
> +{
> +	ctrl->type_ops->minimum(ctrl, 0, ctrl->p_new);
> +
> +	return ptr_to_user(c, ctrl, ctrl->p_new);
> +}
> +
> +/* Helper function: copy the maximum control value back to the caller */
> +static int max_to_user(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
> +{
> +	ctrl->type_ops->maximum(ctrl, 0, ctrl->p_new);
> +
> +	return ptr_to_user(c, ctrl, ctrl->p_new);
> +}
> +
>  /* Helper function: copy the caller-provider value as the new control value */
>  static int user_to_new(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
>  {
> @@ -229,8 +245,8 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
>  		cs->error_idx = i;
>  
>  		if (cs->which &&
> -		    cs->which != V4L2_CTRL_WHICH_DEF_VAL &&
> -		    cs->which != V4L2_CTRL_WHICH_REQUEST_VAL &&
> +		    (cs->which < V4L2_CTRL_WHICH_DEF_VAL ||
> +		     cs->which > V4L2_CTRL_WHICH_MAX_VAL) &&
>  		    V4L2_CTRL_ID2WHICH(id) != cs->which) {
>  			dprintk(vdev,
>  				"invalid which 0x%x or control id 0x%x\n",
> @@ -259,6 +275,15 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
>  			return -EINVAL;
>  		}
>  
> +		if (!(ctrl->flags & V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX) &&
> +		    (cs->which == V4L2_CTRL_WHICH_MIN_VAL ||
> +		     cs->which == V4L2_CTRL_WHICH_MAX_VAL)) {
> +			dprintk(vdev,
> +				"invalid which 0x%x or control id 0x%x\n",
> +				cs->which, id);
> +			return -EINVAL;
> +		}
> +
>  		if (ctrl->cluster[0]->ncontrols > 1)
>  			have_clusters = true;
>  		if (ctrl->cluster[0] != ctrl)
> @@ -368,8 +393,8 @@ static int prepare_ext_ctrls(struct v4l2_ctrl_handler *hdl,
>   */
>  static int class_check(struct v4l2_ctrl_handler *hdl, u32 which)
>  {
> -	if (which == 0 || which == V4L2_CTRL_WHICH_DEF_VAL ||
> -	    which == V4L2_CTRL_WHICH_REQUEST_VAL)
> +	if (which == 0 || (which >= V4L2_CTRL_WHICH_DEF_VAL &&
> +			   which <= V4L2_CTRL_WHICH_MAX_VAL))
>  		return 0;
>  	return find_ref_lock(hdl, which | 1) ? 0 : -EINVAL;
>  }
> @@ -389,10 +414,12 @@ int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
>  	struct v4l2_ctrl_helper *helpers = helper;
>  	int ret;
>  	int i, j;
> -	bool is_default, is_request;
> +	bool is_default, is_request, is_min, is_max;
>  
>  	is_default = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
>  	is_request = (cs->which == V4L2_CTRL_WHICH_REQUEST_VAL);
> +	is_min = (cs->which == V4L2_CTRL_WHICH_MIN_VAL);
> +	is_max = (cs->which == V4L2_CTRL_WHICH_MAX_VAL);
>  
>  	cs->error_idx = cs->count;
>  	cs->which = V4L2_CTRL_ID2WHICH(cs->which);
> @@ -432,13 +459,14 @@ int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
>  
>  		/*
>  		 * g_volatile_ctrl will update the new control values.
> -		 * This makes no sense for V4L2_CTRL_WHICH_DEF_VAL and
> +		 * This makes no sense for V4L2_CTRL_WHICH_DEF_VAL,
> +		 * V4L2_CTRL_WHICH_MIN_VAL, V4L2_CTRL_WHICH_MAX_VAL and
>  		 * V4L2_CTRL_WHICH_REQUEST_VAL. In the case of requests
>  		 * it is v4l2_ctrl_request_complete() that copies the
>  		 * volatile controls at the time of request completion
>  		 * to the request, so you don't want to do that again.
>  		 */
> -		if (!is_default && !is_request &&
> +		if (!is_default && !is_request && !is_min && !is_max &&
>  		    ((master->flags & V4L2_CTRL_FLAG_VOLATILE) ||
>  		    (master->has_volatiles && !is_cur_manual(master)))) {
>  			for (j = 0; j < master->ncontrols; j++)
> @@ -467,6 +495,10 @@ int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
>  				ret = -ENOMEM;
>  			else if (is_request && ref->p_req_valid)
>  				ret = req_to_user(cs->controls + idx, ref);
> +			else if (is_min)
> +				ret = min_to_user(cs->controls + idx, ref->ctrl);
> +			else if (is_max)
> +				ret = max_to_user(cs->controls + idx, ref->ctrl);
>  			else if (is_volatile)
>  				ret = new_to_user(cs->controls + idx, ref->ctrl);
>  			else
> @@ -564,9 +596,11 @@ int try_set_ext_ctrls_common(struct v4l2_fh *fh,
>  
>  	cs->error_idx = cs->count;
>  
> -	/* Default value cannot be changed */
> -	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL) {
> -		dprintk(vdev, "%s: cannot change default value\n",
> +	/* Default/minimum/maximum values cannot be changed */
> +	if (cs->which == V4L2_CTRL_WHICH_DEF_VAL ||
> +	    cs->which == V4L2_CTRL_WHICH_MIN_VAL ||
> +	    cs->which == V4L2_CTRL_WHICH_MAX_VAL) {
> +		dprintk(vdev, "%s: cannot change default/min/max value\n",
>  			video_device_node_name(vdev));
>  		return -EINVAL;
>  	}
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> index f1486ab032cf..ef418165e88d 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
> @@ -182,29 +182,66 @@ static void std_init_compound(const struct v4l2_ctrl *ctrl, u32 idx,
>  	}
>  }
>  
> -void v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
> +static void std_min_compound(const struct v4l2_ctrl *ctrl, u32 idx,
> +			    union v4l2_ctrl_ptr ptr)
> +{
> +	void *p = ptr.p + idx * ctrl->elem_size;
> +
> +	if (ctrl->p_min.p_const)
> +		memcpy(p, ctrl->p_min.p_const, ctrl->elem_size);
> +	else
> +		memset(p, 0, ctrl->elem_size);
> +}
> +
> +static void std_max_compound(const struct v4l2_ctrl *ctrl, u32 idx,
>  			    union v4l2_ctrl_ptr ptr)
> +{
> +	void *p = ptr.p + idx * ctrl->elem_size;
> +
> +	if (ctrl->p_max.p_const)
> +		memcpy(p, ctrl->p_max.p_const, ctrl->elem_size);
> +	else
> +		memset(p, 0, ctrl->elem_size);
> +}
> +
> +static void __v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
> +				     u32 which, union v4l2_ctrl_ptr ptr)
>  {
>  	unsigned int i;
>  	u32 tot_elems = ctrl->elems;
>  	u32 elems = tot_elems - from_idx;
> +	s64 value;
>  
> -	if (from_idx >= tot_elems)
> +	switch (which) {
> +	case V4L2_CTRL_WHICH_DEF_VAL:
> +		value = ctrl->default_value;
> +		break;
> +	case V4L2_CTRL_WHICH_MAX_VAL:
> +		value = ctrl->maximum;
> +		break;
> +	case V4L2_CTRL_WHICH_MIN_VAL:
> +		value = ctrl->minimum;
> +		break;
> +	default:
>  		return;
> +	}
>  
>  	switch (ctrl->type) {
>  	case V4L2_CTRL_TYPE_STRING:
> +		if (which == V4L2_CTRL_WHICH_DEF_VAL)
> +			value = ctrl->minimum;
> +
>  		for (i = from_idx; i < tot_elems; i++) {
>  			unsigned int offset = i * ctrl->elem_size;
>  
> -			memset(ptr.p_char + offset, ' ', ctrl->minimum);
> -			ptr.p_char[offset + ctrl->minimum] = '\0';
> +			memset(ptr.p_char + offset, ' ', value);
> +			ptr.p_char[offset + value] = '\0';
>  		}
>  		break;
>  	case V4L2_CTRL_TYPE_INTEGER64:
> -		if (ctrl->default_value) {
> +		if (value) {
>  			for (i = from_idx; i < tot_elems; i++)
> -				ptr.p_s64[i] = ctrl->default_value;
> +				ptr.p_s64[i] = value;
>  		} else {
>  			memset(ptr.p_s64 + from_idx, 0, elems * sizeof(s64));
>  		}
> @@ -214,9 +251,9 @@ void v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
>  	case V4L2_CTRL_TYPE_MENU:
>  	case V4L2_CTRL_TYPE_BITMASK:
>  	case V4L2_CTRL_TYPE_BOOLEAN:
> -		if (ctrl->default_value) {
> +		if (value) {
>  			for (i = from_idx; i < tot_elems; i++)
> -				ptr.p_s32[i] = ctrl->default_value;
> +				ptr.p_s32[i] = value;
>  		} else {
>  			memset(ptr.p_s32 + from_idx, 0, elems * sizeof(s32));
>  		}
> @@ -226,32 +263,61 @@ void v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
>  		memset(ptr.p_s32 + from_idx, 0, elems * sizeof(s32));
>  		break;
>  	case V4L2_CTRL_TYPE_U8:
> -		memset(ptr.p_u8 + from_idx, ctrl->default_value, elems);
> +		memset(ptr.p_u8 + from_idx, value, elems);
>  		break;
>  	case V4L2_CTRL_TYPE_U16:
> -		if (ctrl->default_value) {
> +		if (value) {
>  			for (i = from_idx; i < tot_elems; i++)
> -				ptr.p_u16[i] = ctrl->default_value;
> +				ptr.p_u16[i] = value;
>  		} else {
>  			memset(ptr.p_u16 + from_idx, 0, elems * sizeof(u16));
>  		}
>  		break;
>  	case V4L2_CTRL_TYPE_U32:
> -		if (ctrl->default_value) {
> +		if (value) {
>  			for (i = from_idx; i < tot_elems; i++)
> -				ptr.p_u32[i] = ctrl->default_value;
> +				ptr.p_u32[i] = value;
>  		} else {
>  			memset(ptr.p_u32 + from_idx, 0, elems * sizeof(u32));
>  		}
>  		break;
>  	default:
> -		for (i = from_idx; i < tot_elems; i++)
> -			std_init_compound(ctrl, i, ptr);
> +		for (i = from_idx; i < tot_elems; i++) {
> +			switch (which) {
> +			case V4L2_CTRL_WHICH_DEF_VAL:
> +				std_init_compound(ctrl, i, ptr);
> +				break;
> +			case V4L2_CTRL_WHICH_MAX_VAL:
> +				std_max_compound(ctrl, i, ptr);
> +				break;
> +			case V4L2_CTRL_WHICH_MIN_VAL:
> +				std_min_compound(ctrl, i, ptr);
> +				break;
> +			}
> +		}
>  		break;
>  	}
>  }
> +
> +void v4l2_ctrl_type_op_init(const struct v4l2_ctrl *ctrl, u32 from_idx,
> +			    union v4l2_ctrl_ptr ptr)
> +{
> +	__v4l2_ctrl_type_op_init(ctrl, from_idx, V4L2_CTRL_WHICH_DEF_VAL, ptr);
> +}
>  EXPORT_SYMBOL(v4l2_ctrl_type_op_init);
>  
> +void v4l2_ctrl_type_op_minimum(const struct v4l2_ctrl *ctrl, u32 from_idx,
> +			       union v4l2_ctrl_ptr ptr)
> +{
> +	__v4l2_ctrl_type_op_init(ctrl, from_idx, V4L2_CTRL_WHICH_MIN_VAL, ptr);
> +}
> +
> +void v4l2_ctrl_type_op_maximum(const struct v4l2_ctrl *ctrl, u32 from_idx,
> +			       union v4l2_ctrl_ptr ptr)
> +{
> +	__v4l2_ctrl_type_op_init(ctrl, from_idx, V4L2_CTRL_WHICH_MAX_VAL, ptr);
> +}
> +
>  void v4l2_ctrl_type_op_log(const struct v4l2_ctrl *ctrl)
>  {
>  	union v4l2_ctrl_ptr ptr = ctrl->p_cur;
> @@ -1293,6 +1359,8 @@ EXPORT_SYMBOL(v4l2_ctrl_type_op_validate);
>  static const struct v4l2_ctrl_type_ops std_type_ops = {
>  	.equal = v4l2_ctrl_type_op_equal,
>  	.init = v4l2_ctrl_type_op_init,
> +	.minimum = v4l2_ctrl_type_op_minimum,
> +	.maximum = v4l2_ctrl_type_op_maximum,
>  	.log = v4l2_ctrl_type_op_log,
>  	.validate = v4l2_ctrl_type_op_validate,
>  };
> @@ -1764,7 +1832,10 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  			s64 min, s64 max, u64 step, s64 def,
>  			const u32 dims[V4L2_CTRL_MAX_DIMS], u32 elem_size,
>  			u32 flags, const char * const *qmenu,
> -			const s64 *qmenu_int, const union v4l2_ctrl_ptr p_def,
> +			const s64 *qmenu_int,
> +			const union v4l2_ctrl_ptr p_def,
> +			const union v4l2_ctrl_ptr p_min,
> +			const union v4l2_ctrl_ptr p_max,
>  			void *priv)
>  {
>  	struct v4l2_ctrl *ctrl;
> @@ -1888,6 +1959,12 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  		break;
>  	}
>  
> +	if (type < V4L2_CTRL_COMPOUND_TYPES &&
> +	    type != V4L2_CTRL_TYPE_BUTTON &&
> +	    type != V4L2_CTRL_TYPE_CTRL_CLASS &&
> +	    type != V4L2_CTRL_TYPE_STRING)
> +		flags |= V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX;
> +
>  	/* Sanity checks */
>  	if (id == 0 || name == NULL || !elem_size ||
>  	    id >= V4L2_CID_PRIVATE_BASE ||
> @@ -1896,6 +1973,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  		handler_set_err(hdl, -ERANGE);
>  		return NULL;
>  	}
> +
>  	err = check_range(type, min, max, step, def);
>  	if (err) {
>  		handler_set_err(hdl, err);
> @@ -1937,6 +2015,10 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  
>  	if (type >= V4L2_CTRL_COMPOUND_TYPES && p_def.p_const)
>  		sz_extra += elem_size;
> +	if (type >= V4L2_CTRL_COMPOUND_TYPES && p_min.p_const)
> +		sz_extra += elem_size;
> +	if (type >= V4L2_CTRL_COMPOUND_TYPES && p_max.p_const)
> +		sz_extra += elem_size;
>  
>  	ctrl = kvzalloc(sizeof(*ctrl) + sz_extra, GFP_KERNEL);
>  	if (ctrl == NULL) {
> @@ -2002,6 +2084,22 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>  		memcpy(ctrl->p_def.p, p_def.p_const, elem_size);
>  	}
>  
> +	if (flags & V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX) {
> +		void *ptr = ctrl->p_def.p;
> +
> +		if (p_min.p_const) {
> +			ptr += elem_size;
> +			ctrl->p_min.p = ptr;
> +			memcpy(ctrl->p_min.p, p_min.p_const, elem_size);
> +		}
> +
> +		if (p_max.p_const) {
> +			ptr += elem_size;
> +			ctrl->p_max.p = ptr;
> +			memcpy(ctrl->p_max.p, p_max.p_const, elem_size);
> +		}
> +	}
> +
>  	ctrl->type_ops->init(ctrl, 0, ctrl->p_cur);
>  	cur_to_new(ctrl);
>  
> @@ -2052,7 +2150,8 @@ struct v4l2_ctrl *v4l2_ctrl_new_custom(struct v4l2_ctrl_handler *hdl,
>  			type, min, max,
>  			is_menu ? cfg->menu_skip_mask : step, def,
>  			cfg->dims, cfg->elem_size,
> -			flags, qmenu, qmenu_int, cfg->p_def, priv);
> +			flags, qmenu, qmenu_int, cfg->p_def, cfg->p_min,
> +			cfg->p_max, priv);
>  	if (ctrl)
>  		ctrl->is_private = cfg->is_private;
>  	return ctrl;
> @@ -2077,7 +2176,8 @@ struct v4l2_ctrl *v4l2_ctrl_new_std(struct v4l2_ctrl_handler *hdl,
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
>  			     min, max, step, def, NULL, 0,
> -			     flags, NULL, NULL, ptr_null, NULL);
> +			     flags, NULL, NULL, ptr_null, ptr_null,
> +			     ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std);
>  
> @@ -2110,7 +2210,8 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_menu(struct v4l2_ctrl_handler *hdl,
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
>  			     0, max, mask, def, NULL, 0,
> -			     flags, qmenu, qmenu_int, ptr_null, NULL);
> +			     flags, qmenu, qmenu_int, ptr_null, ptr_null,
> +			     ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std_menu);
>  
> @@ -2142,7 +2243,8 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_menu_items(struct v4l2_ctrl_handler *hdl,
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
>  			     0, max, mask, def, NULL, 0,
> -			     flags, qmenu, NULL, ptr_null, NULL);
> +			     flags, qmenu, NULL, ptr_null, ptr_null,
> +			     ptr_null, NULL);
>  
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std_menu_items);
> @@ -2150,7 +2252,9 @@ EXPORT_SYMBOL(v4l2_ctrl_new_std_menu_items);
>  /* Helper function for standard compound controls */
>  struct v4l2_ctrl *v4l2_ctrl_new_std_compound(struct v4l2_ctrl_handler *hdl,
>  				const struct v4l2_ctrl_ops *ops, u32 id,
> -				const union v4l2_ctrl_ptr p_def)
> +				const union v4l2_ctrl_ptr p_def,
> +				const union v4l2_ctrl_ptr p_min,
> +				const union v4l2_ctrl_ptr p_max)
>  {
>  	const char *name;
>  	enum v4l2_ctrl_type type;
> @@ -2164,7 +2268,7 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_compound(struct v4l2_ctrl_handler *hdl,
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
>  			     min, max, step, def, NULL, 0,
> -			     flags, NULL, NULL, p_def, NULL);
> +			     flags, NULL, NULL, p_def, p_min, p_max, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_std_compound);
>  
> @@ -2188,7 +2292,8 @@ struct v4l2_ctrl *v4l2_ctrl_new_int_menu(struct v4l2_ctrl_handler *hdl,
>  	}
>  	return v4l2_ctrl_new(hdl, ops, NULL, id, name, type,
>  			     0, max, 0, def, NULL, 0,
> -			     flags, NULL, qmenu_int, ptr_null, NULL);
> +			     flags, NULL, qmenu_int, ptr_null, ptr_null,
> +			     ptr_null, NULL);
>  }
>  EXPORT_SYMBOL(v4l2_ctrl_new_int_menu);
>  
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 9b1de54ce379..db5bd765db3c 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -884,7 +884,9 @@ static bool check_ext_ctrls(struct v4l2_ext_controls *c, unsigned long ioctl)
>  			return false;
>  		break;
>  	case V4L2_CTRL_WHICH_DEF_VAL:
> -		/* Default value cannot be changed */
> +	case V4L2_CTRL_WHICH_MIN_VAL:
> +	case V4L2_CTRL_WHICH_MAX_VAL:
> +		/* Default, minimum or maximum value cannot be changed */
>  		if (ioctl == VIDIOC_S_EXT_CTRLS ||
>  		    ioctl == VIDIOC_TRY_EXT_CTRLS) {
>  			c->error_idx = c->count;
> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> index b0db167a3ac4..9ed7be1e696f 100644
> --- a/include/media/v4l2-ctrls.h
> +++ b/include/media/v4l2-ctrls.h
> @@ -133,6 +133,8 @@ struct v4l2_ctrl_ops {
>   *
>   * @equal: return true if all ctrl->elems array elements are equal.
>   * @init: initialize the value for array elements from from_idx to ctrl->elems.
> + * @minimum: set the value to the minimum value of the control.
> + * @maximum: set the value to the maximum value of the control.
>   * @log: log the value.
>   * @validate: validate the value for ctrl->new_elems array elements.
>   *	Return 0 on success and a negative value otherwise.
> @@ -142,6 +144,10 @@ struct v4l2_ctrl_type_ops {
>  		      union v4l2_ctrl_ptr ptr1, union v4l2_ctrl_ptr ptr2);
>  	void (*init)(const struct v4l2_ctrl *ctrl, u32 from_idx,
>  		     union v4l2_ctrl_ptr ptr);
> +	void (*minimum)(const struct v4l2_ctrl *ctrl, u32 idx,
> +			union v4l2_ctrl_ptr ptr);
> +	void (*maximum)(const struct v4l2_ctrl *ctrl, u32 idx,
> +			union v4l2_ctrl_ptr ptr);
>  	void (*log)(const struct v4l2_ctrl *ctrl);
>  	int (*validate)(const struct v4l2_ctrl *ctrl, union v4l2_ctrl_ptr ptr);
>  };
> @@ -247,6 +253,12 @@ typedef void (*v4l2_ctrl_notify_fnc)(struct v4l2_ctrl *ctrl, void *priv);
>   * @p_def:	The control's default value represented via a union which
>   *		provides a standard way of accessing control types
>   *		through a pointer (for compound controls only).
> + * @p_min:	The control's minimum value represented via a union which
> + *		provides a standard way of accessing control types
> + *		through a pointer (for compound controls only).
> + * @p_max:	The control's maximum value represented via a union which
> + *		provides a standard way of accessing control types
> + *		through a pointer (for compound controls only).
>   * @p_cur:	The control's current value represented via a union which
>   *		provides a standard way of accessing control types
>   *		through a pointer.
> @@ -306,6 +318,8 @@ struct v4l2_ctrl {
>  	} cur;
>  
>  	union v4l2_ctrl_ptr p_def;
> +	union v4l2_ctrl_ptr p_min;
> +	union v4l2_ctrl_ptr p_max;
>  	union v4l2_ctrl_ptr p_new;
>  	union v4l2_ctrl_ptr p_cur;
>  };
> @@ -425,6 +439,8 @@ struct v4l2_ctrl_handler {
>   * @step:	The control's step value for non-menu controls.
>   * @def:	The control's default value.
>   * @p_def:	The control's default value for compound controls.
> + * @p_min:	The control's minimum value for compound controls.
> + * @p_max:	The control's maximum value for compound controls.
>   * @dims:	The size of each dimension.
>   * @elem_size:	The size in bytes of the control.
>   * @flags:	The control's flags.
> @@ -454,6 +470,8 @@ struct v4l2_ctrl_config {
>  	u64 step;
>  	s64 def;
>  	union v4l2_ctrl_ptr p_def;
> +	union v4l2_ctrl_ptr p_min;
> +	union v4l2_ctrl_ptr p_max;
>  	u32 dims[V4L2_CTRL_MAX_DIMS];
>  	u32 elem_size;
>  	u32 flags;
> @@ -723,17 +741,25 @@ struct v4l2_ctrl *v4l2_ctrl_new_std_menu_items(struct v4l2_ctrl_handler *hdl,
>   * @ops:       The control ops.
>   * @id:        The control ID.
>   * @p_def:     The control's default value.
> + * @p_min:     The control's minimum value.
> + * @p_max:     The control's maximum value.
>   *
> - * Sames as v4l2_ctrl_new_std(), but with support to compound controls, thanks
> - * to the @p_def field. Use v4l2_ctrl_ptr_create() to create @p_def from a
> - * pointer. Use v4l2_ctrl_ptr_create(NULL) if the default value of the
> - * compound control should be all zeroes.
> + * Same as v4l2_ctrl_new_std(), but with support for compound controls.
> + * To fill in the @p_def, @p_min and @p_max fields, use v4l2_ctrl_ptr_create()
> + * to convert a pointer to a const union v4l2_ctrl_ptr.
> + * Use v4l2_ctrl_ptr_create(NULL) if you want the default, minimum or maximum
> + * value of the compound control to be all zeroes.
> + * If the compound control does not set the ``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX``
> + * flag, then it does not has minimum and maximum values. In that case just use
> + * v4l2_ctrl_ptr_create(NULL) for the @p_min and @p_max arguments.
>   *
>   */
>  struct v4l2_ctrl *v4l2_ctrl_new_std_compound(struct v4l2_ctrl_handler *hdl,
>  					     const struct v4l2_ctrl_ops *ops,
>  					     u32 id,
> -					     const union v4l2_ctrl_ptr p_def);
> +					     const union v4l2_ctrl_ptr p_def,
> +					     const union v4l2_ctrl_ptr p_min,
> +					     const union v4l2_ctrl_ptr p_max);
>  
>  /**
>   * v4l2_ctrl_new_int_menu() - Create a new standard V4L2 integer menu control.
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 82d86abcf89c..8fdeb5188af5 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1866,6 +1866,8 @@ struct v4l2_ext_controls {
>  #define V4L2_CTRL_WHICH_CUR_VAL   0
>  #define V4L2_CTRL_WHICH_DEF_VAL   0x0f000000
>  #define V4L2_CTRL_WHICH_REQUEST_VAL 0x0f010000
> +#define V4L2_CTRL_WHICH_MIN_VAL   0x0f020000
> +#define V4L2_CTRL_WHICH_MAX_VAL   0x0f030000
>  
>  enum v4l2_ctrl_type {
>  	V4L2_CTRL_TYPE_INTEGER	     = 1,
> @@ -1973,6 +1975,7 @@ struct v4l2_querymenu {
>  #define V4L2_CTRL_FLAG_EXECUTE_ON_WRITE	0x0200
>  #define V4L2_CTRL_FLAG_MODIFY_LAYOUT	0x0400
>  #define V4L2_CTRL_FLAG_DYNAMIC_ARRAY	0x0800
> +#define V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX 0x1000
>  
>  /*  Query flags, to be ORed with the control ID */
>  #define V4L2_CTRL_FLAG_NEXT_CTRL	0x80000000

-- 
Regards,

Laurent Pinchart