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Subject: Re: [PATCH 1/4] v4l2-ctrl: Make display delay and display enable std
 controls
To:     Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Cc:     Kyungmin Park <kyungmin.park@samsung.com>,
        Kamil Debski <kamil@wypas.org>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Nicolas Dufresne <nicolas.dufresne@collabora.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>
References: <20201109173541.10016-1-stanimir.varbanov@linaro.org>
 <20201109173541.10016-2-stanimir.varbanov@linaro.org>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
Message-ID: <e0a49eb2-f4d0-0532-52e0-5bc58ce85ad9@xs4all.nl>
Date:   Wed, 2 Dec 2020 15:09:30 +0100
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On 09/11/2020 18:35, Stanimir Varbanov wrote:
> Make display delay and display delay enable MFC controls standard v4l
> controls. This will allow reuse of the controls for other decoder
> drivers. Also the new proposed controls are now codec agnostic because
> they could be used for any codec.
> 
> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
> ---
>  .../userspace-api/media/v4l/ext-ctrls-codec.rst   | 15 +++++++++++++++
>  drivers/media/v4l2-core/v4l2-ctrls.c              |  4 ++++
>  include/uapi/linux/v4l2-controls.h                |  2 ++
>  3 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index ce728c757eaf..82c9cda40270 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -679,6 +679,21 @@ enum v4l2_mpeg_video_frame_skip_mode -
>      otherwise the decoder expects a single frame in per buffer.
>      Applicable to the decoder, all codecs.
>  
> +``V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY_ENABLE (boolean)``

I'd use _DEC_ instead of _DECODER_.

> +    If the display delay is enabled then the decoder is forced to return
> +    a CAPTURE buffer (decoded frame) after processing a certain number
> +    of OUTPUT buffers. The delay can be set through
> +    ``V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY``. This
> +    feature can be used for example for generating thumbnails of videos.
> +    Applicable to the decoder.

Hmm. Is this: "after processing the first 'display delay' number of OUTPUT buffers."
Or is this: "every 'display delay' number of OUTPUT buffers."

I.e., is it a one-shot thing or a periodical thing?

If it is a one-shot thing, then this should probably be a button type, not
a boolean.

> +
> +``V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY (integer)``
> +    Display delay value for decoder. The decoder is forced to
> +    return a decoded frame after the set 'display delay' number of
> +    frames. If this number is low it may result in frames returned out
> +    of display order, in addition the hardware may still be using the
> +    returned buffer as a reference picture for subsequent frames.

Can this be 0? And if so, what does that mean?

> +
>  ``V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_ENABLE (boolean)``
>      Enable writing sample aspect ratio in the Video Usability
>      Information. Applicable to the H264 encoder.
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index bd7f330c941c..4a21802e026b 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -874,6 +874,8 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_HEADER_MODE:			return "Sequence Header Mode";
>  	case V4L2_CID_MPEG_VIDEO_MAX_REF_PIC:			return "Max Number of Reference Pics";
>  	case V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE:		return "Frame Skip Mode";
> +	case V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY:		return "Display Delay";
> +	case V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY_ENABLE:	return "Display Delay Enable";
>  	case V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP:		return "H263 I-Frame QP Value";
>  	case V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP:		return "H263 P-Frame QP Value";
>  	case V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP:		return "H263 B-Frame QP Value";
> @@ -1221,6 +1223,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  	case V4L2_CID_FLASH_READY:
>  	case V4L2_CID_MPEG_VIDEO_DECODER_MPEG4_DEBLOCK_FILTER:
>  	case V4L2_CID_MPEG_VIDEO_DECODER_SLICE_INTERFACE:
> +	case V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_H264_8X8_TRANSFORM:
> @@ -1256,6 +1259,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  		break;
>  	case V4L2_CID_MPEG_VIDEO_MV_H_SEARCH_RANGE:
>  	case V4L2_CID_MPEG_VIDEO_MV_V_SEARCH_RANGE:
> +	case V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY:
>  		*type = V4L2_CTRL_TYPE_INTEGER;
>  		break;
>  	case V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME:
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 7035f4fb182c..d6b19f8d0022 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -773,6 +773,8 @@ enum v4l2_mpeg_video_frame_skip_mode {
>  	V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_LEVEL_LIMIT	= 1,
>  	V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_BUF_LIMIT	= 2,
>  };
> +#define V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY		(V4L2_CID_MPEG_BASE + 647)
> +#define V4L2_CID_MPEG_VIDEO_DECODER_DISPLAY_DELAY_ENABLE	(V4L2_CID_MPEG_BASE + 648)

This will need to be rebased once this PR is merged:
https://patchwork.linuxtv.org/project/linux-media/patch/d68da172-b251-000f-653d-38a8a4c7b715@xs4all.nl/

>  
>  /*  MPEG-class control IDs specific to the CX2341x driver as defined by V4L2 */
>  #define V4L2_CID_MPEG_CX2341X_BASE				(V4L2_CTRL_CLASS_MPEG | 0x1000)
> 

Regards,

	Hans