Re: [RFC PATCH v6 09/11] media: uapi: Add audio rate controls support

From: Hans Verkuil
Date: Wed Oct 18 2023 - 10:31:36 EST

On 18/10/2023 15:50, Shengjiu Wang wrote:
> On Wed, Oct 18, 2023 at 9:09 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>
>> On 18/10/2023 14:52, Shengjiu Wang wrote:
>>> On Wed, Oct 18, 2023 at 3:58 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>>>
>>>> On 18/10/2023 09:40, Shengjiu Wang wrote:
>>>>> On Wed, Oct 18, 2023 at 3:31 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>>>>>
>>>>>> On 18/10/2023 09:23, Shengjiu Wang wrote:
>>>>>>> On Wed, Oct 18, 2023 at 10:27 AM Shengjiu Wang <shengjiu.wang@xxxxxxxxx> wrote:
>>>>>>>>
>>>>>>>> On Tue, Oct 17, 2023 at 9:37 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>>>>>>>>
>>>>>>>>> On 17/10/2023 15:11, Shengjiu Wang wrote:
>>>>>>>>>> On Mon, Oct 16, 2023 at 9:16 PM Hans Verkuil <hverkuil@xxxxxxxxx> 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@xxxxxxx>
>>>>>>>>>>>> ---
>>>>>>>>>>>> .../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@xxxxxxxxxx/
>>>>>>>>>>>
>>>>>>>>>>> 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?
>>>>>>>>>
>>>>>>>>
>>>>>>>> 'Normal' rate is used to select the prefilter table.
>>>>>>>>
>>>>>>>
>>>>>>> Currently I think we may define
>>>>>>> V4L2_CID_M2M_AUDIO_SOURCE_RATE
>>>>>>> V4L2_CID_M2M_AUDIO_DEST_RATE
>>>>>>
>>>>>> That makes sense.
>>>>>>
>>>>>>> V4L2_CID_M2M_AUDIO_ASRC_RATIO_MOD
>>>>>>
>>>>>> OK, can you document this control? Just write it down in the reply, I just want
>>>>>> to understand how the integer value you set here is used.
>>>>>>
>>>>>
>>>>> It is Q31 value. It is equal to:
>>>>> in_rate_new / out_rate_new - in_rate_old / out_rate_old
>>>>
>>>> So that's not an integer. Also, Q31 is limited to -1...1, and I think
>>>> that's too limiting.
>>>>
>>>> For this having a Q31.32 fixed point type still makes a lot of sense.
>>>>
>>>> I still feel this is a overly complicated API.
>>>>
>>>> See more below...
>>>>
>>>>>
>>>>> Best regards
>>>>> Wang shengjiu
>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Hans
>>>>>>
>>>>>>>
>>>>>>> All of them can be V4L2_CTRL_TYPE_INTEGER.
>>>>>>>
>>>>>>> RATIO_MOD was defined in the very beginning version.
>>>>>>> I think it is better to let users calculate this value.
>>>>>>>
>>>>>>> The reason is:
>>>>>>> if we define the offset for source rate and dest rate in
>>>>>>> driver separately, when offset of source rate is set,
>>>>>>> driver don't know if it needs to wait or not the dest rate
>>>>>>> offset, then go to calculate the ratio_mod.
>>>>
>>>> Ah, in order to update the ratio mod userspace needs to set both source and
>>>> dest rate at the same time to avoid race conditions.
>>>>
>>>> That is perfectly possible in the V4L2 control framework. See:
>>>>
>>>> https://linuxtv.org/downloads/v4l-dvb-apis-new/driver-api/v4l2-controls.html#control-clusters
>>>>
>>>> In practice, isn't it likely that you would fix either the source or
>>>> destination rate, and let the other rate fluctuate? It kind of feels weird
>>>> to me that both source AND destination rates can fluctuate over time.
>>>>
>>> Right, the source and dest rates needn't change in same time.
>>>
>>>> In any case, with a control cluster it doesn't really matter, you can set
>>>> one rate or both rates, and it will be handled atomically.
>>>>
>>>> I feel that the RATIO_MOD control is too hardware specific. This is something
>>>> that should be hidden in the driver.
>>>>
>>>
>>> I will use:
>>>
>>> V4L2_CID_M2M_AUDIO_SOURCE_RATE
>>> V4L2_CID_M2M_AUDIO_DEST_RATE
>>> V4L2_CID_M2M_AUDIO_SOURCE_RATE_OFFSET
>>> V4L2_CID_M2M_AUDIO_DEST_RATE_OFFSET
>>>
>>> 'OFFSET' is V4L2_CTRL_TYPE_FIXED_POINT, which is Q31.32.
>>
>> So now I come back to my original question: why do you need both
>> the rate and the offset? Isn't it enough to set just the rates,
>> as long as that is in fixed point format?
>>
>> Why does the driver need both the 'ideal' rate + the offset?
>>
>> I'm not opposed to this, I'm just trying to understand whether this
>> makes sense.
>>
>> Can't you take e.g. the source and dest rate as starting points
>> when you start streaming? And every time userspace updates one or both
>> of these rates you calculate the ratio_mod compared to the previous rates?
>>
>> Or is there a reason why you need the ideal rates as well? E.g. 48000 or
>> 44100, etc.
>>
>
> ideal rates is used to select prefilter table. the prefilter table is indexed by
> ideal rates.
>
> The asrc has two part: prefilter and resampler filter. The convert ratio is
> applied to rasampler filter part.

Ah! But doesn't this also imply that there are only a limited number of supported
ideal rates? I see the supported_asrc_rate array in sound/soc/fsl/fsl_asrc.c, which
I suspect is in fact that list?

That means that the SOURCE/DEST_RATE controls aren't integers, but instead should
be of type V4L2_CTRL_TYPE_INTEGER_MENU.

How flexible is the resampler? E.g. I see that 12 and 16 kHz are supported, so can I
select 12 kHz as the ideal rate, and an offset of 2000 Hz to convert from 14 kHz to
something else? Or is it much more limited?

I ask, because if it is really flexible, then it is easy to just select 14 kHz and let
the driver find the closest ideal rate.

If, however, it only can support a small range around each ideal rate (e.g. 11900-12100
Hz around the 12000 Hz ideal rate), then userspace needs to know those ideal rates,
and that needs to be exposed through an INTEGER_MENU control.

Regards,

Hans