linux-kernel - Re: [PATCH v2] media: v4l2-ctrl: Add base layer priority id control.

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Date:   Tue, 17 Nov 2020 15:53:03 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Dikshita Agarwal <dikshita@...eaurora.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Cc:     mchehab@...nel.org, ezequiel@...labora.com,
        stanimir.varbanov@...aro.org, vgarodia@...eaurora.org,
        majja@...eaurora.org, Nicolas Dufresne <nicolas@...fresne.ca>
Subject: Re: [PATCH v2] media: v4l2-ctrl: Add base layer priority id control.

Nicolas, can you take a look at this with your codec knowledge?

Some other review comments below:

On 15/10/2020 13:05, Dikshita Agarwal wrote:
> This control indicates the priority id to be applied
> to base layer.
> 
> Signed-off-by: Dikshita Agarwal <dikshita@...eaurora.org>
> ---
>  Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 9 +++++++++
>  drivers/media/v4l2-core/v4l2-ctrls.c                      | 1 +
>  include/uapi/linux/v4l2-controls.h                        | 1 +
>  3 files changed, 11 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 6e9240a..aac1ea3 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -4407,3 +4407,12 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>         to the LTR index max LTR count-1.
>         This is applicable to H264 and HEVC encoder and can be applied using
>         request api.
> +
> +``V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITYID (integer)``

I'd add a_ before the ID, so: V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITY_ID.

> +       Specifies a priority identifier for the NAL unit,
> +       which will be applied to base layer.
> +       By default this value is set to 0 for base layer.
> +       And the next layer will have priority ID assigned as 1,2,3 and so on.
> +       Video encode can't decide the priority id to be applied to a layer
> +       so this has to come from client.
> +       Valid Range: from 0 to 63

I'm slightly rephrasing the text above:

       Specifies a priority identifier for the NAL unit, which will be applied to
       the base layer. By default this value is set to 0 for the base layer,
       and the next layer will have the priority ID assigned as 1, 2, 3 and so on.
       The video encoder can't decide the priority id to be applied to a layer,
       so this has to come from client.
       Valid Range: from 0 to 63.

For which codecs is this applicable? H264 and HEVC? That should be stated. If you
have a reference to the corresponding sections that describe this, then that would
be nice to add.

> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index 046198f..c973058 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -952,6 +952,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_LTR_COUNT:			return "LTR Count";
>  	case V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX:		return "Mark LTR frame index";
>  	case V4L2_CID_MPEG_VIDEO_USE_LTR_FRAME:			return "Use LTR Frame";
> +	case V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITYID:		return "Base Layer Priority ID";
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS:		return "MPEG-2 Slice Parameters";
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_QUANTIZATION:		return "MPEG-2 Quantization Matrices";
>  	case V4L2_CID_MPEG_VIDEO_FWHT_PARAMS:			return "FWHT Stateless Parameters";
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 3801372..433e119 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -418,6 +418,7 @@ enum v4l2_mpeg_video_multi_slice_mode {
>  #define V4L2_CID_MPEG_VIDEO_LTR_COUNT                  (V4L2_CID_MPEG_BASE+230)
>  #define V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX            (V4L2_CID_MPEG_BASE+231)
>  #define V4L2_CID_MPEG_VIDEO_USE_LTR_FRAME              (V4L2_CID_MPEG_BASE+232)
> +#define V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITYID       (V4L2_CID_MPEG_BASE+233)
>  
>  /* CIDs for the MPEG-2 Part 2 (H.262) codec */
>  #define V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL			(V4L2_CID_MPEG_BASE+270)
> 

Regards,

	Hans