Re: [PATCH 1/2] media: media.h: Add a pad flag MEDIA_PAD_FL_METADATA

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Dafna,

Thank you for the patch.

On Wed, Mar 25, 2020 at 10:27:03PM +0100, Dafna Hirschfeld wrote:
> Add a flag to the flags field of 'struct media_pad_desc'
> that indicates that the data transmitted by the pad is
> metadata.
> 
> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
> ---
>  Documentation/media/uapi/mediactl/media-types.rst | 4 ++++
>  include/uapi/linux/media.h                        | 1 +
>  2 files changed, 5 insertions(+)
> 
> diff --git a/Documentation/media/uapi/mediactl/media-types.rst b/Documentation/media/uapi/mediactl/media-types.rst
> index 3af6a414b501..4ca902478971 100644
> --- a/Documentation/media/uapi/mediactl/media-types.rst
> +++ b/Documentation/media/uapi/mediactl/media-types.rst
> @@ -361,6 +361,7 @@ Types and flags used to represent the media graph elements
>  .. _MEDIA-PAD-FL-SINK:
>  .. _MEDIA-PAD-FL-SOURCE:
>  .. _MEDIA-PAD-FL-MUST-CONNECT:
> +.. _MEDIA-PAD-FL-METADATA:
>  
>  .. flat-table:: Media pad flags
>      :header-rows:  0
> @@ -381,6 +382,9 @@ Types and flags used to represent the media graph elements
>  	  configuration dependent) for the pad to need enabled links even
>  	  when this flag isn't set; the absence of the flag doesn't imply
>  	  there is none.
> +    *  -  ``MEDIA_PAD_FL_METADATA``
> +       -  This flag indicates that the data transmitted by the pad is of
> +          type metadata.
>  
>  
>  One and only one of ``MEDIA_PAD_FL_SINK`` and ``MEDIA_PAD_FL_SOURCE``
> diff --git a/include/uapi/linux/media.h b/include/uapi/linux/media.h
> index 383ac7b7d8f0..ae37226eb5c9 100644
> --- a/include/uapi/linux/media.h
> +++ b/include/uapi/linux/media.h
> @@ -210,6 +210,7 @@ struct media_entity_desc {
>  #define MEDIA_PAD_FL_SINK			(1 << 0)
>  #define MEDIA_PAD_FL_SOURCE			(1 << 1)
>  #define MEDIA_PAD_FL_MUST_CONNECT		(1 << 2)
> +#define MEDIA_PAD_FL_METADATA			(1 << 3)

I think we need to reserve a few bits here. We'll have more than
metadata. Audio comes to mind, there will likely be more. Having
independent flags would not only waste a bit of space in the bitfield
(not that we're about to run out of bits, but still), but would make it
possible to specify invalid configurations such as MEDIA_PAD_FL_METADATA
| MEDIA_PAD_FL_AUDIO. And now that I've written this, I realize that
audio metadata could be a thing, so maybe a metadata flag is actually
the best option :-)

There are pros and cons for both options, so I won't recommend one.

>  struct media_pad_desc {
>  	__u32 entity;		/* entity ID */

-- 
Regards,

Laurent Pinchart