Re: [PATCH v9 10/15] media: uapi: Add V4L2_CTRL_TYPE_FIXED_POINT

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On 13/11/2023 11:42, Laurent Pinchart wrote:
> On Mon, Nov 13, 2023 at 11:29:09AM +0100, Hans Verkuil wrote:
>> Hi Shengjiu,
>>
>> On 10/11/2023 06:48, Shengjiu Wang wrote:
>>> Fixed point controls are used by the user to configure
>>> a fixed point value in 64bits, which Q31.32 format.
>>>
>>> Signed-off-by: Shengjiu Wang <shengjiu.wang@xxxxxxx>
>>
>> This patch adds a new control type. This is something that also needs to be
>> tested by v4l2-compliance, and for that we need to add support for this to
>> one of the media test-drivers. The best place for that is the vivid driver,
>> since that has already a bunch of test controls for other control types.
>>
>> See e.g. VIVID_CID_INTEGER64 in vivid-ctrls.c.
>>
>> Can you add a patch adding a fixed point test control to vivid?
> 
> I don't think V4L2_CTRL_TYPE_FIXED_POINT is a good idea. This seems to
> relate more to units than control types. We have lots of fixed-point
> values in controls already, using the 32-bit and 64-bit integer control
> types. They use various locations for the decimal point, depending on
> the control. If we want to make this more explicit to users, we should
> work on adding unit support to the V4L2 controls.

"Fixed Point" is not a unit, it's a type. 'Db', 'Hz' etc. are units.

A quick "git grep -i "fixed point" Documentation/userspace-api/media/'
only shows a single driver specific control (dw100.rst).

I'm not aware of other controls in mainline that use fixed point.

Note that V4L2_CTRL_TYPE_FIXED_POINT is a Q31.32 format. By setting
min/max/step you can easily map that to just about any QN.M format where
N <= 31 and M <= 32.

In the case of dw100 it is a bit different in that it is quite specialized
and it had to fit in 16 bits.

Regards,

	Hans

> 
>>> ---
>>>  .../userspace-api/media/v4l/vidioc-g-ext-ctrls.rst  | 13 +++++++------
>>>  .../userspace-api/media/v4l/vidioc-queryctrl.rst    |  9 ++++++++-
>>>  .../userspace-api/media/videodev2.h.rst.exceptions  |  1 +
>>>  drivers/media/v4l2-core/v4l2-ctrls-api.c            |  5 ++++-
>>>  drivers/media/v4l2-core/v4l2-ctrls-core.c           |  2 ++
>>>  include/uapi/linux/videodev2.h                      |  1 +
>>>  6 files changed, 23 insertions(+), 8 deletions(-)
>>>
>>> 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 e8475f9fd2cf..e7e5d78dc11e 100644
>>> --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
>>> @@ -162,13 +162,13 @@ still cause this situation.
>>>      * - __s32
>>>        - ``value``
>>>        - New value or current value. Valid if this control is not of type
>>> -	``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
>>> -	not set.
>>> +	``V4L2_CTRL_TYPE_INTEGER64``, ``V4L2_CTRL_TYPE_FIXED_POINT`` and
>>> +	``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is not set.
>>>      * - __s64
>>>        - ``value64``
>>>        - New value or current value. Valid if this control is of type
>>> -	``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
>>> -	not set.
>>> +	``V4L2_CTRL_TYPE_INTEGER64``, ``V4L2_CTRL_TYPE_FIXED_POINT`` and
>>> +	``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is not set.
>>>      * - char *
>>>        - ``string``
>>>        - A pointer to a string. Valid if this control is of type
>>> @@ -193,8 +193,9 @@ still cause this situation.
>>>      * - __s64 *
>>>        - ``p_s64``
>>>        - A pointer to a matrix control of signed 64-bit values. Valid if
>>> -        this control is of type ``V4L2_CTRL_TYPE_INTEGER64`` and
>>> -        ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set.
>>> +        this control is of type ``V4L2_CTRL_TYPE_INTEGER64``,
>>> +        ``V4L2_CTRL_TYPE_FIXED_POINT`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
>>> +        is set.
>>>      * - struct :c:type:`v4l2_area` *
>>>        - ``p_area``
>>>        - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
>>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> index 4d38acafe8e1..f3995ec57044 100644
>>> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> @@ -235,7 +235,8 @@ See also the examples in :ref:`control`.
>>>        - ``default_value``
>>>        - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
>>>  	``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
>>> -	or ``_U16`` control. Not valid for other types of controls.
>>> +	``_FIXED_POINT`` or ``_U16`` control. Not valid for other types of
>>> +	controls.
>>>  
>>>  	.. note::
>>>  
>>> @@ -549,6 +550,12 @@ See also the examples in :ref:`control`.
>>>        - n/a
>>>        - A struct :c:type:`v4l2_ctrl_av1_film_grain`, containing AV1 Film Grain
>>>          parameters for stateless video decoders.
>>> +    * - ``V4L2_CTRL_TYPE_FIXED_POINT``
>>> +      - any
>>> +      - any
>>> +      - any
>>> +      - A 64-bit integer valued control, containing parameter which is
>>> +        Q31.32 format.
>>>  
>>>  .. raw:: latex
>>>  
>>> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>> index e61152bb80d1..2faa5a2015eb 100644
>>> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>> @@ -167,6 +167,7 @@ replace symbol V4L2_CTRL_TYPE_AV1_SEQUENCE :c:type:`v4l2_ctrl_type`
>>>  replace symbol V4L2_CTRL_TYPE_AV1_TILE_GROUP_ENTRY :c:type:`v4l2_ctrl_type`
>>>  replace symbol V4L2_CTRL_TYPE_AV1_FRAME :c:type:`v4l2_ctrl_type`
>>>  replace symbol V4L2_CTRL_TYPE_AV1_FILM_GRAIN :c:type:`v4l2_ctrl_type`
>>> +replace symbol V4L2_CTRL_TYPE_FIXED_POINT :c:type:`v4l2_ctrl_type`
>>>  
>>>  # V4L2 capability defines
>>>  replace define V4L2_CAP_VIDEO_CAPTURE device-capabilities
>>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
>>> index 002ea6588edf..e6a0fb8d6791 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
>>> @@ -57,6 +57,7 @@ static int ptr_to_user(struct v4l2_ext_control *c,
>>>  		return copy_to_user(c->string, ptr.p_char, len + 1) ?
>>>  		       -EFAULT : 0;
>>>  	case V4L2_CTRL_TYPE_INTEGER64:
>>> +	case V4L2_CTRL_TYPE_FIXED_POINT:
>>>  		c->value64 = *ptr.p_s64;
>>>  		break;
>>>  	default:
>>> @@ -132,6 +133,7 @@ static int user_to_new(struct v4l2_ext_control *c, struct v4l2_ctrl *ctrl)
>>>  
>>>  	switch (ctrl->type) {
>>>  	case V4L2_CTRL_TYPE_INTEGER64:
>>> +	case V4L2_CTRL_TYPE_FIXED_POINT:
>>>  		*ctrl->p_new.p_s64 = c->value64;
>>>  		break;
>>>  	case V4L2_CTRL_TYPE_STRING:
>>> @@ -540,7 +542,8 @@ static int validate_ctrls(struct v4l2_ext_controls *cs,
>>>  		 */
>>>  		if (ctrl->is_ptr)
>>>  			continue;
>>> -		if (ctrl->type == V4L2_CTRL_TYPE_INTEGER64)
>>> +		if (ctrl->type == V4L2_CTRL_TYPE_INTEGER64 ||
>>> +		    ctrl->type == V4L2_CTRL_TYPE_FIXED_POINT)
>>>  			p_new.p_s64 = &cs->controls[i].value64;
>>>  		else
>>>  			p_new.p_s32 = &cs->controls[i].value;
>>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> index a662fb60f73f..9d50df0d9874 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> @@ -1187,6 +1187,7 @@ static int std_validate_elem(const struct v4l2_ctrl *ctrl, u32 idx,
>>>  	case V4L2_CTRL_TYPE_INTEGER:
>>>  		return ROUND_TO_RANGE(ptr.p_s32[idx], u32, ctrl);
>>>  	case V4L2_CTRL_TYPE_INTEGER64:
>>> +	case V4L2_CTRL_TYPE_FIXED_POINT:
>>>  		/*
>>>  		 * We can't use the ROUND_TO_RANGE define here due to
>>>  		 * the u64 divide that needs special care.
>>> @@ -1779,6 +1780,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>>>  	/* Prefill elem_size for all types handled by std_type_ops */
>>>  	switch ((u32)type) {
>>>  	case V4L2_CTRL_TYPE_INTEGER64:
>>> +	case V4L2_CTRL_TYPE_FIXED_POINT:
>>>  		elem_size = sizeof(s64);
>>>  		break;
>>>  	case V4L2_CTRL_TYPE_STRING:
>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>> index cf8c44595a1d..9482ac66a675 100644
>>> --- a/include/uapi/linux/videodev2.h
>>> +++ b/include/uapi/linux/videodev2.h
>>> @@ -1903,6 +1903,7 @@ enum v4l2_ctrl_type {
>>>  	V4L2_CTRL_TYPE_STRING        = 7,
>>>  	V4L2_CTRL_TYPE_BITMASK       = 8,
>>>  	V4L2_CTRL_TYPE_INTEGER_MENU  = 9,
>>> +	V4L2_CTRL_TYPE_FIXED_POINT   = 10,
>>>  
>>>  	/* Compound types are >= 0x0100 */
>>>  	V4L2_CTRL_COMPOUND_TYPES     = 0x0100,
> 





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