Em Fri, 25 Aug 2017 15:42:21 +0200 Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > On 25/08/17 14:52, 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 | 53 +++++++++++++++++++++++++++++++++++ > > 1 file changed, 53 insertions(+) > > > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > > index 9b98d10d5153..bbd1887f83a0 100644 > > --- a/Documentation/media/uapi/v4l/open.rst > > +++ b/Documentation/media/uapi/v4l/open.rst > > @@ -6,6 +6,59 @@ > > Opening and Closing Devices > > *************************** > > > > +Types of V4L2 hardware control > > +============================== > > + > > +V4L2 hardware is usually complex: support for the hardware is implemented > > +via a main driver (also known as bridge driver) and often several > > +additional drivers. The main driver always exposes one or > > +more **V4L2 device nodes** (see :ref:`v4l2_device_naming`). > > + > > +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). 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 hardware > > +control. The entire V4L2 hardware is controlled via the > > +**V4L2 device nodes**. We refer to this kind of control as > > +**V4L2 device node centric** (or, simply, **vdev-centric**). > > + > > +Since the end of 2010, a new type of V4L2 hardware control was added, in > > Just drop 'the end of'. > > s/, in/ in/ I anded by changing it to: Later (kernel 2.6.39), > > > +order to support complex devices that are common for embedded systems. > > +Those hardware are controlled mainly via the media controller and > > Such hardware is > > > +sub-devices. So, they are called: **Media controller centric** > > +(or, simply, "**MC-centric**"). > > + > > +For **vdev-centric** hardware control, the hardware is controlled via > > +the **V4L2 device nodes**. They may optionally support the > > +:ref:`media controller API <media_controller>` as well, in order to let > > +the application to know with device nodes are available. > > to know with -> know which > > > + > > +.. note:: > > + > > + A **vdev-centric** may optionally expose V4L2 sub-devices via > > I propose adding 'also' before 'expose' to indicate that it is in > addition to the V4L2 device nodes that were mentioned in the previous > paragraph. > > > + :ref:`sub-device API <subdev>`. In that case, it has to implement > > + the :ref:`media controller API <media_controller>` as well. > > + > > +For **MC-centric** hardware control, before using the V4L2 hardware, > > +it is required to set the pipelines via the > > I'd reword this a bit: > > For **MC-centric** hardware control it is required to configure the pipelines > via the :ref:`media controller API <media_controller>` before the hardware can be used. > > > +:ref:`media controller API <media_controller>`. For those devices, the > > s/those/such/ > > > +sub-devices' configuration can be controlled via the > > +:ref:`sub-device API <subdev>`, whith creates one device node > > s/whith/which/ > > > +per sub-device. > > + > > +In summary, for **MC-centric** hardware control: > > + > > +- The **V4L2 device** node is responsible for controlling the streaming > > + features; > > +- The **media controller device** is responsible to setup the pipelines; > > +- The **V4L2 sub-devices** are responsible for sub-device > > + specific settings. > > + > > + > > +.. _v4l2_device_naming: > > > > V4L2 Device Node Naming > > ======================= Changes done. I'll place on a new version of this series. > > > > The only thing I am not sure about is vdev-centric vs V4L2-centric. 'Laziness while > typing' is not a convincing argument :-) Despite the laziness of playing a lot with shifts to type V4L2-centric, the thing that bothers me with V4L2 is that the subdev API is part of V4L2 spec. So, IMHO, it is still a confusing name. As this actually refers to "V4L2 Device Node", with is now properly specified (due to patch 1/3), "vdev" is a good shortcut for it. Let's reverse the question: what's wrong with "vdev-centric"? Thanks, Mauro
