Message-ID: <0ae6d9e1-bdd9-45ab-9749-8b0cb5c624ff@xs4all.nl>
Date:   Tue, 17 Oct 2023 15:37:13 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>, sakari.ailus@....fi,
        tfiga@...omium.org, m.szyprowski@...sung.com, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiubo.Lee@...il.com, festevam@...il.com, nicoleotsuka@...il.com,
        lgirdwood@...il.com, broonie@...nel.org, perex@...ex.cz,
        tiwai@...e.com, alsa-devel@...a-project.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v6 09/11] media: uapi: Add audio rate controls support

On 17/10/2023 15:11, Shengjiu Wang wrote:
> On Mon, Oct 16, 2023 at 9:16 PM Hans Verkuil <hverkuil@...all.nl> wrote:
>>
>> Hi Shengjiu,
>>
>> On 13/10/2023 10:31, Shengjiu Wang wrote:
>>> Fixed point controls are used by the user to configure
>>> the audio sample rate to driver.
>>>
>>> Add V4L2_CID_ASRC_SOURCE_RATE and V4L2_CID_ASRC_DEST_RATE
>>> new IDs for ASRC rate control.
>>>
>>> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
>>> ---
>>>  .../userspace-api/media/v4l/common.rst        |  1 +
>>>  .../media/v4l/ext-ctrls-fixed-point.rst       | 36 +++++++++++++++++++
>>>  .../media/v4l/vidioc-g-ext-ctrls.rst          |  4 +++
>>>  .../media/v4l/vidioc-queryctrl.rst            |  7 ++++
>>>  .../media/videodev2.h.rst.exceptions          |  1 +
>>>  drivers/media/v4l2-core/v4l2-ctrls-core.c     |  5 +++
>>>  drivers/media/v4l2-core/v4l2-ctrls-defs.c     |  4 +++
>>>  include/media/v4l2-ctrls.h                    |  2 ++
>>>  include/uapi/linux/v4l2-controls.h            | 13 +++++++
>>>  include/uapi/linux/videodev2.h                |  3 ++
>>>  10 files changed, 76 insertions(+)
>>>  create mode 100644 Documentation/userspace-api/media/v4l/ext-ctrls-fixed-point.rst
>>>
>>> diff --git a/Documentation/userspace-api/media/v4l/common.rst b/Documentation/userspace-api/media/v4l/common.rst
>>> index ea0435182e44..35707edffb13 100644
>>> --- a/Documentation/userspace-api/media/v4l/common.rst
>>> +++ b/Documentation/userspace-api/media/v4l/common.rst
>>> @@ -52,6 +52,7 @@ applicable to all devices.
>>>      ext-ctrls-fm-rx
>>>      ext-ctrls-detect
>>>      ext-ctrls-colorimetry
>>> +    ext-ctrls-fixed-point
>>
>> Rename this to ext-ctrls-audio-m2m.
>>
>>>      fourcc
>>>      format
>>>      planar-apis
>>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-fixed-point.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-fixed-point.rst
>>> new file mode 100644
>>> index 000000000000..2ef6e250580c
>>> --- /dev/null
>>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-fixed-point.rst
>>> @@ -0,0 +1,36 @@
>>> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
>>> +
>>> +.. _fixed-point-controls:
>>> +
>>> +***************************
>>> +Fixed Point Control Reference
>>
>> This is for audio controls. "Fixed Point" is just the type, and it doesn't make
>> sense to group fixed point controls. But it does make sense to group the audio
>> controls.
>>
>> V4L2 controls can be grouped into classes. Basically it is a way to put controls
>> into categories, and for each category there is also a control that gives a
>> description of the class (see 2.15.15 in
>> https://linuxtv.org/downloads/v4l-dvb-apis-new/driver-api/v4l2-controls.html#introduction)
>>
>> If you use e.g. 'v4l2-ctl -l' to list all the controls, then you will see that
>> they are grouped based on what class of control they are.
>>
>> So I think it would be a good idea to create a new control class for M2M audio controls,
>> instead of just adding them to the catch-all 'User Controls' class.
>>
>> Search e.g. for V4L2_CTRL_CLASS_COLORIMETRY and V4L2_CID_COLORIMETRY_CLASS to see how
>> it is done.
>>
>> M2M_AUDIO would probably be a good name for the class.
>>
>>> +***************************
>>> +
>>> +These controls are intended to support an asynchronous sample
>>> +rate converter.
>>
>> Add ' (ASRC).' at the end to indicate the common abbreviation for
>> that.
>>
>>> +
>>> +.. _v4l2-audio-asrc:
>>> +
>>> +``V4L2_CID_ASRC_SOURCE_RATE``
>>> +    sets the resampler source rate.
>>> +
>>> +``V4L2_CID_ASRC_DEST_RATE``
>>> +    sets the resampler destination rate.
>>
>> Document the unit (Hz) for these two controls.
>>
>>> +
>>> +.. c:type:: v4l2_ctrl_fixed_point
>>> +
>>> +.. cssclass:: longtable
>>> +
>>> +.. tabularcolumns:: |p{1.5cm}|p{5.8cm}|p{10.0cm}|
>>> +
>>> +.. flat-table:: struct v4l2_ctrl_fixed_point
>>> +    :header-rows:  0
>>> +    :stub-columns: 0
>>> +    :widths:       1 1 2
>>> +
>>> +    * - __u32
>>
>> Hmm, shouldn't this be __s32?
>>
>>> +      - ``integer``
>>> +      - integer part of fixed point value.
>>> +    * - __s32
>>
>> and this __u32?
>>
>> You want to be able to use this generic type as a signed value.
>>
>>> +      - ``fractional``
>>> +      - fractional part of fixed point value, which is Q31.
>>> 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 f9f73530a6be..1811dabf5c74 100644
>>> --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
>>> @@ -295,6 +295,10 @@ still cause this situation.
>>>        - ``p_av1_film_grain``
>>>        - A pointer to a struct :c:type:`v4l2_ctrl_av1_film_grain`. Valid if this control is
>>>          of type ``V4L2_CTRL_TYPE_AV1_FILM_GRAIN``.
>>> +    * - struct :c:type:`v4l2_ctrl_fixed_point` *
>>> +      - ``p_fixed_point``
>>> +      - A pointer to a struct :c:type:`v4l2_ctrl_fixed_point`. Valid if this control is
>>> +        of type ``V4L2_CTRL_TYPE_FIXED_POINT``.
>>>      * - void *
>>>        - ``ptr``
>>>        - A pointer to a compound type which can be an N-dimensional array
>>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> index 4d38acafe8e1..9285f4f39eed 100644
>>> --- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
>>> @@ -549,6 +549,13 @@ 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``
>>> +      - n/a
>>> +      - n/a
>>> +      - n/a
>>> +      - A struct :c:type:`v4l2_ctrl_fixed_point`, containing parameter which has
>>> +        integer part and fractional part, i.e. audio sample rate.
>>> +
>>>
>>>  .. 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-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> index a662fb60f73f..7a616ac91059 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
>>> @@ -1168,6 +1168,8 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
>>>               if (!area->width || !area->height)
>>>                       return -EINVAL;
>>>               break;
>>> +     case V4L2_CTRL_TYPE_FIXED_POINT:
>>> +             break;
>>
>> Hmm, this would need this patch 'v4l2-ctrls: add support for V4L2_CTRL_WHICH_MIN/MAX_VAL':
>>
>> https://patchwork.linuxtv.org/project/linux-media/patch/20231010022136.1504015-7-yunkec@google.com/
>>
>> since min and max values are perfectly fine for a fixed point value.
>>
>> Even a step value (currently not supported in that patch) would make sense.
>>
>> But I wonder if we couldn't simplify this: instead of creating a v4l2_ctrl_fixed_point,
>> why not represent the fixed point value as a Q31.32. Then the standard
>> minimum/maximum/step values can be used, and it acts like a regular V4L2_TYPE_INTEGER64.
>>
>> Except that both userspace and drivers need to multiply it with 2^-32 to get the actual
>> value.
>>
>> So in enum v4l2_ctrl_type add:
>>
>>         V4L2_CTRL_TYPE_FIXED_POINT = 10,
>>
>> (10, because it is no longer a compound type).
> 
> Seems we don't need V4L2_CTRL_TYPE_FIXED_POINT, just use V4L2_TYPE_INTEGER64?
> 
> The reason I use the 'integer' and 'fractional' is that I want
> 'integer' to be the normal sample
> rate, for example 48kHz.  The 'fractional' is the difference with
> normal sample rate.
> 
> For example, the rate = 47998.12345.  so integer = 48000,  fractional= -1.87655.
> 
> So if we use s64 for rate, then in driver need to convert the rate to
> the closed normal
> sample rate + fractional.

That wasn't what the documentation said :-)

So this is really two controls: one for the 'normal sample rate' (whatever 'normal'
means in this context) and the offset to the actual sample rate.

Presumably the 'normal' sample rate is set once, while the offset changes
regularly.

But why do you need the 'normal' sample rate? With audio resampling I assume
you resample from one rate to another, so why do you need a third 'normal'
rate?

Regards,

	Hans

> 
> best regards
> wang shengjiu
> 
>>
>>>
>>>       default:
>>>               return -EINVAL;
>>> @@ -1868,6 +1870,9 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
>>>       case V4L2_CTRL_TYPE_AREA:
>>>               elem_size = sizeof(struct v4l2_area);
>>>               break;
>>> +     case V4L2_CTRL_TYPE_FIXED_POINT:
>>> +             elem_size = sizeof(struct v4l2_ctrl_fixed_point);
>>> +             break;
>>>       default:
>>>               if (type < V4L2_CTRL_COMPOUND_TYPES)
>>>                       elem_size = sizeof(s32);
>>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>> index 8696eb1cdd61..d8f232df6b6a 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>> @@ -1602,6 +1602,10 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>>>       case V4L2_CID_COLORIMETRY_HDR10_MASTERING_DISPLAY:
>>>               *type = V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY;
>>>               break;
>>> +     case V4L2_CID_ASRC_SOURCE_RATE:
>>> +     case V4L2_CID_ASRC_DEST_RATE:
>>> +             *type = V4L2_CTRL_TYPE_FIXED_POINT;
>>> +             break;
>>>       default:
>>>               *type = V4L2_CTRL_TYPE_INTEGER;
>>>               break;
>>> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
>>> index 59679a42b3e7..645e4cccafc7 100644
>>> --- a/include/media/v4l2-ctrls.h
>>> +++ b/include/media/v4l2-ctrls.h
>>> @@ -56,6 +56,7 @@ struct video_device;
>>>   * @p_av1_tile_group_entry:  Pointer to an AV1 tile group entry structure.
>>>   * @p_av1_frame:             Pointer to an AV1 frame structure.
>>>   * @p_av1_film_grain:                Pointer to an AV1 film grain structure.
>>> + * @p_fixed_point:           Pointer to a struct v4l2_ctrl_fixed_point.
>>>   * @p:                               Pointer to a compound value.
>>>   * @p_const:                 Pointer to a constant compound value.
>>>   */
>>> @@ -89,6 +90,7 @@ union v4l2_ctrl_ptr {
>>>       struct v4l2_ctrl_av1_tile_group_entry *p_av1_tile_group_entry;
>>>       struct v4l2_ctrl_av1_frame *p_av1_frame;
>>>       struct v4l2_ctrl_av1_film_grain *p_av1_film_grain;
>>> +     struct v4l2_ctrl_fixed_point *p_fixed_point;
>>>       void *p;
>>>       const void *p_const;
>>>  };
>>> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
>>> index c3604a0a3e30..91096259e3ea 100644
>>> --- a/include/uapi/linux/v4l2-controls.h
>>> +++ b/include/uapi/linux/v4l2-controls.h
>>> @@ -112,6 +112,8 @@ enum v4l2_colorfx {
>>>
>>>  /* last CID + 1 */
>>>  #define V4L2_CID_LASTP1                         (V4L2_CID_BASE+44)
>>> +#define V4L2_CID_ASRC_SOURCE_RATE            (V4L2_CID_BASE + 45)
>>> +#define V4L2_CID_ASRC_DEST_RATE                      (V4L2_CID_BASE + 46)
>>
>> This patch needs to be split in three parts:
>>
>> 1) Add the new M2M_AUDIO control class,
>> 2) Add the new V4L2_CTRL_TYPE_FIXED_POINT type,
>> 3) Add the new controls.
>>
>> These are all independent changes, so separating them makes it easier to
>> review.
>>
>>>
>>>  /* USER-class private control IDs */
>>>
>>> @@ -3488,4 +3490,15 @@ struct v4l2_ctrl_av1_film_grain {
>>>  #define V4L2_CID_MPEG_MFC51_BASE        V4L2_CID_CODEC_MFC51_BASE
>>>  #endif
>>>
>>> +/**
>>> + * struct v4l2_ctrl_fixed_point - fixed point parameter.
>>> + *
>>> + * @rate_integer: integer part of fixed point value.
>>> + * @rate_fractional: fractional part of fixed point value
>>> + */
>>> +struct v4l2_ctrl_fixed_point {
>>> +     __u32 integer;
>>
>> __s32?
>>
>>> +     __u32 fractional;
>>> +};
>>> +
>>>  #endif
>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>> index 2ac7b989394c..3ef32c09c2fa 100644
>>> --- a/include/uapi/linux/videodev2.h
>>> +++ b/include/uapi/linux/videodev2.h
>>> @@ -1888,6 +1888,7 @@ struct v4l2_ext_control {
>>>               struct v4l2_ctrl_av1_tile_group_entry __user *p_av1_tile_group_entry;
>>>               struct v4l2_ctrl_av1_frame __user *p_av1_frame;
>>>               struct v4l2_ctrl_av1_film_grain __user *p_av1_film_grain;
>>> +             struct v4l2_ctrl_fixed_point __user *p_fixed_point;
>>>               void __user *ptr;
>>>       };
>>>  } __attribute__ ((packed));
>>> @@ -1966,6 +1967,8 @@ enum v4l2_ctrl_type {
>>>       V4L2_CTRL_TYPE_AV1_TILE_GROUP_ENTRY = 0x281,
>>>       V4L2_CTRL_TYPE_AV1_FRAME            = 0x282,
>>>       V4L2_CTRL_TYPE_AV1_FILM_GRAIN       = 0x283,
>>> +
>>> +     V4L2_CTRL_TYPE_FIXED_POINT          = 0x290,
>>>  };
>>>
>>>  /*  Used in the VIDIOC_QUERYCTRL ioctl for querying controls */
>>
>> Regards,
>>
>>         Hans

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