linux-kernel - Re: [PATCH v5 1/3] media: videodev2: Add flag to unconditionnaly enumerate pixels formats

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Message-ID: <07a6b2a7-9884-40cb-b29a-3b30731d9686@collabora.com>
Date: Wed, 31 Jul 2024 09:00:44 +0200
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
To: Hans Verkuil <hverkuil-cisco@...all.nl>, 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 v5 1/3] media: videodev2: Add flag to unconditionnaly
 enumerate pixels formats


Le 30/07/2024 à 09:19, Hans Verkuil a écrit :
> On 30/07/2024 09:08, Hans Verkuil wrote:
>> On 22/07/2024 17:05, Benjamin Gaignard wrote:
>>> When the index field is ORed with V4L2_FMT_FLAG_ENUM_ALL the driver
>>> will ignore any configuration and enumerate all the possible formats.
>>> Drivers which do not support this flag yet always return an EINVAL
>>> error code.
>>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>> ---
>>> changes in version 5:
>>> - Reset the proposal to follow Hans's advices
>>> - Add new flag to be used with index field.
>>>
>>>   .../userspace-api/media/v4l/vidioc-enum-fmt.rst      | 12 +++++++++++-
>>>   .../userspace-api/media/videodev2.h.rst.exceptions   |  1 +
>>>   include/uapi/linux/videodev2.h                       |  3 +++
>>>   3 files changed, 15 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..12e1e65e6a71 100644
>>> --- a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>>> @@ -85,7 +85,11 @@ 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
>> You need to start a new paragraph before 'When'. Otherwise you might read
>> that the 'When' sentence is somehow related to the previous sentence.
>>
>>> +        index is ORed with V4L2_FMT_FLAG_ENUM_ALL the driver will ignore
>>> +        any configuration and enumerate all the possible formats. Drivers
>> I'd rephrase this a little bit:
>>
>> the driver will enumerate all the possible formats, ignoring any limitations
>> from the current configuration.
>>
>> And after that I would like to see an example of a use-case.
> Should the flag be kept on return of VIDIOC_ENUM_FMT or should it be cleared?
> For reference: VIDIOC_QUERYCTRL will clear the V4L2_CTRL_FLAG_NEXT_CTRL flag.
>
> Regardless of what we pick, it should be documented.

I believe most of the flags are cleared in v4l2 so I will to do the same and
document it.

>
> Regards,
>
> 	Hans
>
>>> +        which do not support this flag yet always return an ``EINVAL``
>>> +        error code.
>>>       * - __u32
>>>         - ``type``
>>>         - Type of the data stream, set by the application. Only these types
>>> @@ -234,6 +238,12 @@ 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_FMT_FLAG_ENUM_ALL``
>> I am not really happy with this name since the prefix is identical to that
>> of other V4L2_FMT_FLAG_ defines. How about: V4L2_FMTDESC_FLAG_ENUM_ALL?
>> Or V4L2_FMT_IDX_ENUM_ALL?
>>
>>> +      - 0x80000000
>>> +      - When the applications ORs ``index`` with ``V4L2_FMT_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``.
>>>   
>>>   Return Value
>>>   ============
>>> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>> index bdc628e8c1d6..8dc10a500fc6 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_FMT_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..3d11f91273a1 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_FMT_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
>>
>