Re: [PATCH v4 0/2] Enumerate all pixels formats

[Benjamin Gaignard <benjamin.gaignard@collabora.com>]

Le 19/07/2024 à 14:57, Hans Verkuil a écrit :
> On 17/07/2024 15:14, Benjamin Gaignard wrote:
>> The goal of this series is to let userland applications enumerate
>> all the supported pixels formats of a stateless decoder without
>> setting all the possible codec-dependent control.
>> That offer a simplest solution for applications to discover
>> supported pixels formats and possibly let them doing smarter
>> choice between stateless decoders.
>>
>> An example of how it can be used in GStreamer to discover the
>> supported pixels formats for stateless decoder is available here:
>> https://gitlab.freedesktop.org/benjamin.gaignard1/gstreamer/-/commits/v4l2codecs_enum_all_supported_formats?ref_type=heads
> So effectively specifying this flag makes ENUM_FMT also return
> formats that do not match the bit depth.
>
> So the AV1 (for example) compressed video uses e.g. 8 bit depth, but instead of just
> listing only 8 bit uncompressed pixelformats, you want to list them for any
> bit depth.
>
> But what is the point of that if the decoder can't decode 8 bit compressed to,
> say, 10 bit uncompressed video?

No decoder will do 8 bits to 10 bits (as far I knows).
The point is to be able to say that decoder could produce 10 bit frames without
setting a full sps/pps for each case (and for each supported codec).

>
> I actually thought that this flag would just list all formats, independent
> of the output format (e.g. AV1, H264, etc.), but that does not appear to be
> the case? I.e., if capture pixelformat X is only available with AV1, will that still
> be listed if the output pixel is set to H264?
>
> I think you need to describe a real use-case here, and I am not convinced about
> the name of the flag either.

I may have miss something but yes the goal is to list all formats independently
of the output format.
When a SoC have multiple decoders for the same codec, knowing the supported formats
is key to select the better one.
Since I will have to do more iteration, feel free to provide a better name for the
flag(s). I'm always bad for naming this kind of thing.


>
>> changes in version 4:
>> - Explicitly document that the new flags are targeting mem2mem devices.
>>
>> changes in version 3:
>> - Add a flag to inform userspace application that driver
>>    as take care of the flag.
>>
>> changes in version 2:
>> - Clarify documentation.
>> - Only keep V4L2_FMT_FLAG_ALL_FORMATS flag in ioctl.
>>
>> Benjamin
>>
>> Benjamin Gaignard (2):
>>    media: videodev2: Add flags to unconditionnaly enumerate pixels
>>      formats
> I.e.: it is not unconditionally, it still depends on the chosen codec.
>
> Regards,
>
> 	Hans
>
>>    media: verisilicon: Use V4L2_FMT_FLAG_ENUM_ALL_FORMATS flag
>>
>>   .../media/v4l/dev-stateless-decoder.rst          |  6 ++++++
>>   .../userspace-api/media/v4l/vidioc-enum-fmt.rst  | 11 +++++++++++
>>   .../media/videodev2.h.rst.exceptions             |  2 ++
>>   drivers/media/platform/verisilicon/hantro_v4l2.c | 16 +++++++++++++---
>>   drivers/media/v4l2-core/v4l2-ioctl.c             |  3 +++
>>   include/uapi/linux/videodev2.h                   |  2 ++
>>   6 files changed, 37 insertions(+), 3 deletions(-)
>>
>

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