Hi Mauro, Thanks for the update. A few more small comments below. On Fri, Aug 25, 2017 at 06:40:05AM -0300, Mauro Carvalho Chehab wrote: > From: "mchehab@xxxxxxxxxxxxxxxx" <mchehab@xxxxxxxxxxxxxxxx> > > When we added support for omap3, back in 2010, we added a new > type of V4L2 devices that aren't fully controlled via the V4L2 > device node. Yet, we never made it clear, at the V4L2 spec, > about the differences between both types. > > Let's document them with the current implementation. > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> > --- > Documentation/media/uapi/v4l/open.rst | 50 +++++++++++++++++++++++++++++++++++ > 1 file changed, 50 insertions(+) > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > index afd116edb40d..a72d142897c0 100644 > --- a/Documentation/media/uapi/v4l/open.rst > +++ b/Documentation/media/uapi/v4l/open.rst > @@ -6,6 +6,56 @@ > Opening and Closing Devices > *************************** > > +Types of V4L2 hardware control > +============================== > + > +V4L2 devices are usually complex: they are implemented via a main driver and > +often several additional drivers. The main driver always exposes one or > +more **V4L2 device** devnodes (see :ref:`v4l2_device_naming`). s/V4L2 device\*\* devnodes/V4L2 device nodes\*\*/ (As you also have a few paragraphs below.) > + > +The other drivers are called **V4L2 sub-devices** and provide control to > +other parts of the hardware usually connected via a serial bus (like > +I²C, SMBus or SPI). They can be implicitly controlled directly by the s/They/Depending on the main driver, they/ > +main driver or explicitly through via the **V4L2 sub-device API** interface. Through or via, but not both. " interface" is redundant. > + > +When V4L2 was originally designed, there was only one type of device control. > +The entire device was controlled via the **V4L2 device nodes**. We refer to > +this kind of control as **V4L2 device node centric** (or, simply, > +**vdev-centric**). s/vdev-centric/V4L2-centric/ ? > + > +Since the end of 2010, a new type of V4L2 device control was added in order > +to support complex devices that are common for embedded systems. Those > +devices are controlled mainly via the media controller and sub-devices. > +So, they're called: **Media controller centric** (or, simply, > +"**MC-centric**"). > + > +For **vdev-centric** control, the device and their corresponding hardware > +pipelines are controlled via the **V4L2 device** node. They may optionally I'd add highlighting to " node" as well. > +expose via the :ref:`media controller API <media_controller>`. > + > +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 > +sub-devices' configuration can be controlled via the > +:ref:`sub-device API <subdev>`, with creates one device node per sub device. > + > +In summary, for **MC-centric** devices: > + > +- The **V4L2 device** node is responsible for controlling the streaming > + features; Same here. Or, just remove node. The other device nodes are just as much nodes as this one. > +- The **media controller device** is responsible to setup the pipelines; > +- The **V4L2 sub-devices** are responsible for sub-device > + specific settings. > + > +.. note:: > + > + A **vdev-centric** may optionally expose V4L2 sub-devices via > + :ref:`sub-device API <subdev>`. In that case, it has to implement > + the :ref:`media controller API <media_controller>` as well. Looks good! > + > + > + > +.. _v4l2_device_naming: > > Device Naming > ============= -- Kind regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx
