linux-kernel - Re: [PATCH] media: videodev2: add V4L2_FMT_FLAG_NO_SOURCE

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Date:   Thu, 29 Nov 2018 10:01:07 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Maxime Jourdan <mjourdan@...libre.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Tomasz Figa <tfiga@...omium.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: videodev2: add V4L2_FMT_FLAG_NO_SOURCE_CHANGE

On 10/04/2018 03:37 PM, Maxime Jourdan wrote:
> When a v4l2 driver exposes V4L2_EVENT_SOURCE_CHANGE, some (usually
> OUTPUT) formats may not be able to trigger this event.
> 
> Add a enum_fmt format flag to tag those specific formats.

I think I missed (or forgot) some discussion about this since I have no
idea why this flag is needed. What's the use-case?

Regards,

	Hans

> 
> Signed-off-by: Maxime Jourdan <mjourdan@...libre.com>
> ---
>  Documentation/media/uapi/v4l/vidioc-enum-fmt.rst | 5 +++++
>  include/uapi/linux/videodev2.h                   | 5 +++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst b/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> index 019c513df217..e0040b36ac43 100644
> --- a/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> @@ -116,6 +116,11 @@ one until ``EINVAL`` is returned.
>        - This format is not native to the device but emulated through
>  	software (usually libv4l2), where possible try to use a native
>  	format instead for better performance.
> +    * - ``V4L2_FMT_FLAG_NO_SOURCE_CHANGE``
> +      - 0x0004
> +      - The event ``V4L2_EVENT_SOURCE_CHANGE`` is not supported
> +	for this format.
> +
>  
>  
>  Return Value
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 3a65951ca51e..a28acee1cb52 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -723,8 +723,9 @@ struct v4l2_fmtdesc {
>  	__u32		    reserved[4];
>  };
>  
> -#define V4L2_FMT_FLAG_COMPRESSED 0x0001
> -#define V4L2_FMT_FLAG_EMULATED   0x0002
> +#define V4L2_FMT_FLAG_COMPRESSED	0x0001
> +#define V4L2_FMT_FLAG_EMULATED		0x0002
> +#define V4L2_FMT_FLAG_NO_SOURCE_CHANGE	0x0004
>  
>  	/* Frame Size and frame rate enumeration */
>  /*
>