linux-kernel - Re: [PATCH v6 1/3] media: videodev2: Add flag to unconditionally enumerate pixel formats

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Message-ID: <9281e270-01a9-434d-b19a-92978cdbdcc5@xs4all.nl>
Date: Wed, 7 Aug 2024 10:46:21 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>, mchehab@...nel.org,
 ezequiel@...guardiasur.com.ar
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v6 1/3] media: videodev2: Add flag to unconditionally
 enumerate pixel formats

On 07/08/2024 10:39, Hans Verkuil wrote:
> On 31/07/2024 11:34, Benjamin Gaignard wrote:
>> When the index is ORed with V4L2_FMTDESC_FLAG_ENUM_ALL the
>> driver clears the flag and enumerate all the possible formats,
>> ignoring any limitations from the current configuration.
>> Drivers which do not support this flag yet always return an EINVAL.
>>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>> ---
>> change in version 6:
>> - Change flag name.
>> - Improve documentation.
>>
>>  .../userspace-api/media/v4l/vidioc-enum-fmt.rst  | 16 +++++++++++++++-
>>  .../media/videodev2.h.rst.exceptions             |  1 +
>>  include/uapi/linux/videodev2.h                   |  3 +++
>>  3 files changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>> index 3adb3d205531..1112dc9044b2 100644
>> --- a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>> +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>> @@ -85,7 +85,15 @@ the ``mbus_code`` field is handled differently:
>>      * - __u32
>>        - ``index``
>>        - Number of the format in the enumeration, set by the application.
>> -	This is in no way related to the ``pixelformat`` field.
>> +        This is in no way related to the ``pixelformat`` field.
>> +        When the index is ORed with ``V4L2_FMTDESC_FLAG_ENUM_ALL`` the
>> +        driver clears the flag and enumerate all the possible formats,
> 
> enumerate -> enumerates
> 
>> +        ignoring any limitations from the current configuration. Drivers
>> +        which do not support this flag yet always return an ``EINVAL``
> 
> Drop the 'yet'.
> 
> But this raises a question: should this flag only be supported by drivers
> that can actually return different format lists depending on this flag?
> 
> Or can it be supported as well by a driver where this makes no difference?
> 
> I'm inclined to limit it to drivers that actually can return different
> results. If nothing else, that will indicate to the application that this
> is actually possible.
> 
> If we agree on that, then that should be documented as well.

I also think that this flag makes no sense for drivers that have
V4L2_CAP_IO_MC set, since in that case the list of returned formats shall
not depend on the active configuration (see
https://hverkuil.home.xs4all.nl/spec/userspace-api/v4l/vidioc-enum-fmt.html ).

I think this should be mentioned in the documentation and tested for in the
compliance test.

Regards,

	Hans

> 
>> +        error code.
>> +        Formats enumerated when using ``V4L2_FMTDESC_FLAG_ENUM_ALL`` flag
>> +        shouldn't be used when calling :c:func:`VIDIOC_ENUM_FRAMESIZES`
>> +        or :c:func:`VIDIOC_ENUM_FRAMEINTERVALS`.
>>      * - __u32
>>        - ``type``
>>        - Type of the data stream, set by the application. Only these types
>> @@ -234,6 +242,12 @@ the ``mbus_code`` field is handled differently:
>>  	valid. The buffer consists of ``height`` lines, each having ``width``
>>  	Data Units of data and the offset (in bytes) between the beginning of
>>  	each two consecutive lines is ``bytesperline``.
>> +    * - ``V4L2_FMTDESC_FLAG_ENUM_ALL``
>> +      - 0x80000000
>> +      - When the applications ORs ``index`` with ``V4L2_FMTDESC_FLAG_ENUM_ALL`` flag
>> +        the driver enumerates all the possible pixel formats without taking care
>> +        of any already set configuration. Drivers which do not support this flag
>> +        yet, always return ``EINVAL``.
> 
> Drop 'yet'
> 
>>  
>>  Return Value
>>  ============
>> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>> index bdc628e8c1d6..0a9ea9686c24 100644
>> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>> @@ -216,6 +216,7 @@ replace define V4L2_FMT_FLAG_CSC_YCBCR_ENC fmtdesc-flags
>>  replace define V4L2_FMT_FLAG_CSC_HSV_ENC fmtdesc-flags
>>  replace define V4L2_FMT_FLAG_CSC_QUANTIZATION fmtdesc-flags
>>  replace define V4L2_FMT_FLAG_META_LINE_BASED fmtdesc-flags
>> +replace define V4L2_FMTDESC_FLAG_ENUM_ALL fmtdesc-flags
>>  
>>  # V4L2 timecode types
>>  replace define V4L2_TC_TYPE_24FPS timecode-type
>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>> index 4e91362da6da..421a30cb0c51 100644
>> --- a/include/uapi/linux/videodev2.h
>> +++ b/include/uapi/linux/videodev2.h
>> @@ -904,6 +904,9 @@ struct v4l2_fmtdesc {
>>  #define V4L2_FMT_FLAG_CSC_QUANTIZATION		0x0100
>>  #define V4L2_FMT_FLAG_META_LINE_BASED		0x0200
>>  
>> +/*  Format description flag, to be ORed with the index */
>> +#define V4L2_FMTDESC_FLAG_ENUM_ALL		0x80000000
>> +
>>  	/* Frame Size and frame rate enumeration */
>>  /*
>>   *	F R A M E   S I Z E   E N U M E R A T I O N
> 
> Regards,
> 
> 	Hans
>