Re: [PATCH] media: uapi: h264: clarify num_ref_idx_l[01]_(default_)active fields

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

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Hi,

On Thu 05 Sep 19, 13:42, Philipp Zabel wrote:
> To explain why num_ref_idx_active_override_flag is not part of the API,
> describe how the num_ref_idx_l[01]_active_minus1 fields and the
> num_ref_idx_l[01]_default_active_minus1 fields are used, depending on
> whether the decoder parses slice headers itself or not.

Is there any particular reason why this is preferable to exposing the flag?
It feels like having the flag around sticks closer to the bitstream,
so it's more straightforward for everyone.

In case there's only one set of fields exposed by the hardware (and it doesn't
do slice parsing itself), we could always check the flag in the driver and use
either the default PPS values or the slice-specific values there.

What do you think?

Cheers,

Paul

> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
>  Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> index bc5dd8e76567..b9834625a939 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -1630,10 +1630,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>        -
>      * - __u8
>        - ``num_ref_idx_l0_default_active_minus1``
> -      -
> +      - This field is only used by decoders that parse slices themselves.
>      * - __u8
>        - ``num_ref_idx_l1_default_active_minus1``
> -      -
> +      - This field is only used by decoders that parse slices themselves.
>      * - __u8
>        - ``weighted_bipred_idc``
>        -
> @@ -1820,10 +1820,14 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>        -
>      * - __u8
>        - ``num_ref_idx_l0_active_minus1``
> -      -
> +      - This field is used by decoders that do not parse slices themselves.
> +        If num_ref_idx_active_override_flag is not set, this field must be
> +        set to the value of num_ref_idx_l0_default_active_minus1.
>      * - __u8
>        - ``num_ref_idx_l1_active_minus1``
> -      -
> +      - This field is used by decoders that do not parse slices themselves.
> +        If num_ref_idx_active_override_flag is not set, this field must be
> +        set to the value of num_ref_idx_l1_default_active_minus1.
>      * - __u32
>        - ``slice_group_change_cycle``
>        -
> -- 
> 2.20.1
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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