On 09/27/17 15:23, Mauro Carvalho Chehab wrote:
>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
> ---
> Documentation/media/uapi/v4l/open.rst | 40 +++++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> index 18030131ef77..f603bc9b49a0 100644
> --- a/Documentation/media/uapi/v4l/open.rst
> +++ b/Documentation/media/uapi/v4l/open.rst
> @@ -7,6 +7,46 @@ Opening and Closing Devices
> ***************************
>
>
> +.. _v4l2_hardware_control:
> +
> +
> +Types of V4L2 media hardware control
> +====================================
> +
> +V4L2 hardware periferal is usually complex: support for it is
peripheral (in several places...)
> +implemented via a V4L2 main driver and often by several additional drivers.
> +The main driver always exposes one or more **V4L2 device nodes**
> +(see :ref:`v4l2_device_naming`) with are responsible for implementing
> +data streaming, if applicable.
> +
> +The other drivers are called **V4L2 sub-devices** and provide control to
> +other hardware components usually connected via a serial bus (like
> +I²C, SMBus or SPI). Depending on the main driver, they can be implicitly
> +controlled directly by the main driver or explicitly via
> +the **V4L2 sub-device API** (see :ref:`subdev`).
> +
> +When V4L2 was originally designed, there was only one type of
> +media hardware control: via the **V4L2 device nodes**. We refer to this kind
> +of control as **V4L2 device node centric** (or, simply, "**vdevnode-centric**").
> +
> +Later (kernel 2.6.39), a new type of periferal control was
> +added in order to support complex media hardware that are common for embedded
> +systems. This type of periferal is controlled mainly via the media
> +controller and V4L2 sub-devices. So, it is called
> +**Media controller centric** (or, simply, "**MC-centric**") control.
> +
> +For **vdevnode-centric** media hardware control, the media hardware is
> +controlled via the **V4L2 device nodes**. They may optionally support the
> +:ref:`media controller API <media_controller>` as well,
> +in order to inform the application which device nodes are available
> +(see :ref:`related`).
> +
> +For **MC-centric** media hardware control it is required to configure
> +the pipelines via the :ref:`media controller API <media_controller>` before
> +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.
> +
> .. _v4l2_device_naming:
>
> V4L2 Device Node Naming
>
--
~Randy
