linux-kernel - Re: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices

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Date:   Mon, 28 Aug 2017 11:41:58 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
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@...radead.org>,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric
 devices

On 26/08/17 13:53, Mauro Carvalho Chehab wrote:
> 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@...pensource.com>
> ---
>  Documentation/media/uapi/v4l/open.rst            | 7 +++++++
>  Documentation/media/uapi/v4l/vidioc-querycap.rst | 5 +++++
>  Documentation/media/videodev2.h.rst.exceptions   | 1 +
>  include/uapi/linux/videodev2.h                   | 2 ++
>  4 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> index 64b1de047b1b..d0930fc170f0 100644
> --- a/Documentation/media/uapi/v4l/open.rst
> +++ b/Documentation/media/uapi/v4l/open.rst
> @@ -46,6 +46,13 @@ the periferal can be used. For such devices, the sub-devices' configuration
>  can be controlled via the :ref:`sub-device API <subdev>`, which creates one
>  device node per sub-device.
>  
> +.. attention::
> +
> +   Devices that require **mc-centric** hardware peripheral control should

MC-centric

As mentioned in my review of a previous patch I dislike the term "peripheral".
I think it should be dropped here.

> +   report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
> +   (see :ref:`VIDIOC_QUERYCAP`).
> +
> +
>  In summary, for **MC-centric** hardware peripheral control:
>  
>  - The **V4L2 device** node is responsible for controlling the streaming
> diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> index 12e0d9a63cd8..2b08723375bc 100644
> --- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> @@ -252,6 +252,11 @@ specification the ioctl returns an ``EINVAL`` error code.
>      * - ``V4L2_CAP_TOUCH``
>        - 0x10000000
>        - This is a touch device.
> +    * - ``V4L2_MC_CENTRIC``
> +      - 0x20000000
> +      - Indicates that the device require **mc-centric** hardware

MC-centric

> +        control, and thus can't be used by **v4l2-centric** applications.

vdev-centric

TBD: I still think I prefer V4L2-centric over vdev-centric.

> +        See :ref:`v4l2_hardware_control` for more details.
>      * - ``V4L2_CAP_DEVICE_CAPS``
>        - 0x80000000
>        - The driver fills the ``device_caps`` field. This capability can
> diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
> index a5cb0a8686ac..b51a575f9f75 100644
> --- a/Documentation/media/videodev2.h.rst.exceptions
> +++ b/Documentation/media/videodev2.h.rst.exceptions
> @@ -157,6 +157,7 @@ replace define V4L2_CAP_META_CAPTURE device-capabilities
>  replace define V4L2_CAP_READWRITE device-capabilities
>  replace define V4L2_CAP_ASYNCIO device-capabilities
>  replace define V4L2_CAP_STREAMING device-capabilities
> +replace define V4L2_CAP_MC_CENTRIC device-capabilities
>  replace define V4L2_CAP_DEVICE_CAPS device-capabilities
>  replace define V4L2_CAP_TOUCH device-capabilities
>  
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 45cf7359822c..7b490fe97980 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_MC_CENTRIC             0x20000000  /* Device require mc-centric hardware control */

requires
MC-centric

> +
>  #define V4L2_CAP_DEVICE_CAPS            0x80000000  /* sets device capabilities field */
>  
>  /*
> 

Regards,

	Hans