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Subject: Re: [PATCH v7 1/2] media: v4l2-ctrl: add controls for long term
 reference.
To:     Dikshita Agarwal <dikshita@codeaurora.org>,
        linux-media@vger.kernel.org, stanimir.varbanov@linaro.org
Cc:     linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        vgarodia@codeaurora.org
References: <1614769787-26922-1-git-send-email-dikshita@codeaurora.org>
 <1614769787-26922-2-git-send-email-dikshita@codeaurora.org>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
Message-ID: <d3309b63-4816-5fc3-cc38-0f78f2affc04@xs4all.nl>
Date:   Fri, 5 Mar 2021 09:38:28 +0100
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Hi Dikshita,

On 03/03/2021 12:09, Dikshita Agarwal wrote:
> Long Term Reference (LTR) frames are the frames that are encoded
> sometime in the past and stored in the DPB buffer list to be used
> as reference to encode future frames.
> This change adds controls to enable this feature.
> 
> Signed-off-by: Dikshita Agarwal <dikshita@codeaurora.org>
> ---
>  .../userspace-api/media/v4l/ext-ctrls-codec.rst         | 17 +++++++++++++++++
>  drivers/media/v4l2-core/v4l2-ctrls.c                    | 14 ++++++++++++++
>  include/uapi/linux/v4l2-controls.h                      |  3 +++
>  3 files changed, 34 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 00944e9..21fa9a5 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -3646,3 +3646,20 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>      so this has to come from client.
>      This is applicable to H264 and valid Range is from 0 to 63.
>      Source Rec. ITU-T H.264 (06/2019); G.7.4.1.1, G.8.8.1.
> +
> +``V4L2_CID_MPEG_VIDEO_LTR_COUNT (integer)``
> +    Specifies the maximum number of Long Term Reference (LTR) frames at any
> +    given time that the encoder can keep.
> +    This is applicable to the H264 and HEVC encoders.
> +
> +``V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX (integer)``
> +    The current frame is marked as a Long Term Reference (LTR) frame

You mentioned earlier in a reply to me that:

"The driver implementation ensures that whenever the LTR control is
received, it applies to the frame received after that. Not to frame which would be
encoded next."

That behavior is not clear from the text.

Wouldn't this be a better text:

"After setting this control the frame that will be queued next
 will be marked as a Long Term Reference (LTR) frame"

"current frame" isn't precise enough.

> +    and given this LTR index which ranges from 0 to LTR_COUNT-1.
> +    This is applicable to the H264 and HEVC encoders.
> +    Source Rec. ITU-T H.264 (06/2019); Table 7.9
> +
> +``V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES (bitmask)``
> +    Specifies the Long Term Reference (LTR) frame(s) to be used for
> +    encoding the current frame.

Same here. I assume that here too this control applies to the next queued
frame.

> +    This provides a bitmask which consists of bits [0, LTR_COUNT-1].
> +    This is applicable to the H264 and HEVC encoders.

Regards,

	Hans

> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index 016cf62..4d444de 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -951,6 +951,9 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_REPEAT_SEQ_HEADER:		return "Repeat Sequence Header";
>  	case V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME:		return "Force Key Frame";
>  	case V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITY_ID:		return "Base Layer Priority ID";
> +	case V4L2_CID_MPEG_VIDEO_LTR_COUNT:			return "LTR Count";
> +	case V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX:		return "Frame LTR Index";
> +	case V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES:		return "Use LTR Frames";
>  	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_FWHT_I_FRAME_QP:				return "FWHT I-Frame QP Value";
> @@ -1278,6 +1281,17 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  	case V4L2_CID_MPEG_VIDEO_MV_V_SEARCH_RANGE:
>  		*type = V4L2_CTRL_TYPE_INTEGER;
>  		break;
> +	case V4L2_CID_MPEG_VIDEO_LTR_COUNT:
> +		*type = V4L2_CTRL_TYPE_INTEGER;
> +		break;
> +	case V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX:
> +		*type = V4L2_CTRL_TYPE_INTEGER;
> +		*flags |= V4L2_CTRL_FLAG_EXECUTE_ON_WRITE;
> +		break;
> +	case V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES:
> +		*type = V4L2_CTRL_TYPE_BITMASK;
> +		*flags |= V4L2_CTRL_FLAG_EXECUTE_ON_WRITE;
> +		break;
>  	case V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME:
>  	case V4L2_CID_PAN_RESET:
>  	case V4L2_CID_TILT_RESET:
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 039c0d7..fedbb54 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -428,6 +428,9 @@ enum v4l2_mpeg_video_multi_slice_mode {
>  #define V4L2_CID_MPEG_VIDEO_MV_V_SEARCH_RANGE		(V4L2_CID_CODEC_BASE+228)
>  #define V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME		(V4L2_CID_CODEC_BASE+229)
>  #define V4L2_CID_MPEG_VIDEO_BASELAYER_PRIORITY_ID	(V4L2_CID_CODEC_BASE+230)
> +#define V4L2_CID_MPEG_VIDEO_LTR_COUNT			(V4L2_CID_CODEC_BASE+231)
> +#define V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX		(V4L2_CID_CODEC_BASE+232)
> +#define V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES		(V4L2_CID_CODEC_BASE+233)
>  
>  /* CIDs for the MPEG-2 Part 2 (H.262) codec */
>  #define V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL			(V4L2_CID_CODEC_BASE+270)
>