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

From: Hans Verkuil
Date: Mon Nov 13 2023 - 05:57:00 EST

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,
>