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SubjectRe: [PATCH v7 1/2] media: v4l2-ctrl: add controls for long term reference.
Hi Hans,

Thanks for your comments.
I Will update the documentation based on your suggestion in the next
patch.

Thanks,
Dikshita

On 2021-03-05 14:08, Hans Verkuil wrote:
> 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)
>>

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