linux-kernel - Re: [PATCH 2/3] media: videodev2: add a flag for vdev-centric devices

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Message-ID: <4f771cfa-0e0d-3548-a363-6470b32a6634@cisco.com>
Date:   Fri, 25 Aug 2017 11:44:27 +0200
From:   Hans Verkuil <hansverk@...co.com>
To:     Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Cc:     Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Mauro Carvalho Chehab <mchehab@...radead.org>,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>
Subject: Re: [PATCH 2/3] media: videodev2: add a flag for vdev-centric devices

On 08/25/2017 11:40 AM, Mauro Carvalho Chehab wrote:
> From: Mauro Carvalho Chehab <mchehab@....samsung.com>
> 
> As both vdev-centric and mc-centric devices may implement the
> same APIs, we need a flag to allow userspace to distinguish
> between them.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@....samsung.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
> ---
>  Documentation/media/uapi/v4l/open.rst            | 6 ++++++
>  Documentation/media/uapi/v4l/vidioc-querycap.rst | 4 ++++
>  include/uapi/linux/videodev2.h                   | 2 ++
>  3 files changed, 12 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> index a72d142897c0..eb3f0ec57edb 100644
> --- a/Documentation/media/uapi/v4l/open.rst
> +++ b/Documentation/media/uapi/v4l/open.rst
> @@ -33,6 +33,12 @@ For **vdev-centric** control, the device and their corresponding hardware
>  pipelines are controlled via the **V4L2 device** node. They may optionally
>  expose via the :ref:`media controller API <media_controller>`.
>  
> +.. note::
> +
> +   **vdev-centric** devices should report V4L2_VDEV_CENTERED

You mean CENTRIC, not CENTERED.

But I would change this to MC_CENTRIC: the vast majority of drivers are VDEV centric,
so it makes a lot more sense to keep that as the default and only set the cap for
MC-centric drivers.

Regards,

	Hans

> +   :c:type:`v4l2_capability` flag (see :ref:`VIDIOC_QUERYCAP`).
> +
> +
>  For **MC-centric** control, before using the V4L2 device, it is required to
>  set the hardware pipelines via the
>  :ref:`media controller API <media_controller>`. For those devices, the
> diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> index 12e0d9a63cd8..4856821b7608 100644
> --- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> @@ -252,6 +252,10 @@ specification the ioctl returns an ``EINVAL`` error code.
>      * - ``V4L2_CAP_TOUCH``
>        - 0x10000000
>        - This is a touch device.
> +    * - ``V4L2_VDEV_CENTERED``
> +      - 0x20000000
> +      - This is controlled via V4L2 device nodes (radio, video, vbi,
> +        sdr
>      * - ``V4L2_CAP_DEVICE_CAPS``
>        - 0x80000000
>        - The driver fills the ``device_caps`` field. This capability can
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 45cf7359822c..d89090d99042 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -460,6 +460,8 @@ struct v4l2_capability {
>  
>  #define V4L2_CAP_TOUCH                  0x10000000  /* Is a touch device */
>  
> +#define V4L2_CAP_VDEV_CENTERED          0x20000000  /* V4L2 Device is controlled via V4L2 device devnode */
> +
>  #define V4L2_CAP_DEVICE_CAPS            0x80000000  /* sets device capabilities field */
>  
>  /*
>