Em Fri, 25 Aug 2017 10:59:40 +0200 Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > On 24/08/17 14:07, 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> > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx> > > --- > > Documentation/media/uapi/v4l/open.rst | 47 +++++++++++++++++++++++++++++++++++ > > 1 file changed, 47 insertions(+) > > > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > > index afd116edb40d..cf522d9bb53c 100644 > > --- a/Documentation/media/uapi/v4l/open.rst > > +++ b/Documentation/media/uapi/v4l/open.rst > > @@ -6,6 +6,53 @@ > > Opening and Closing Devices > > *************************** > > > > +Types of V4L2 device control > > I don't like calling this 'device control'. Mostly because the word 'device' can > mean almost anything and is very overused. > > How about "hardware control"? Ok. > > > +============================ > > + > > +V4L2 devices are usually complex: they're implemented via a main driver and > > they're -> they are > > (contractions like "they're" aren't normally used in formal texts) > > > +often several additional drivers. The main driver always exposes one or > > +more **V4L2 device** devnodes (see :ref:`v4l2_device_naming`). The other > > +devices are called **V4L2 sub-devices**. They are usually controlled via a > > +serial bus (I2C or SMBus). > > + > > +When V4L2 started, there was only one type of device control. The entire > > started -> was originally designed > > > +device was controlled via the **V4L2 device nodes**. We refer to this > > +kind of control as **V4L2 device-centric** (or, simply, **device-centric**). > > For the same reason as mentioned above I prefer "device node-centric" or > "devnode-centric". "device" is too ambiguous. As I wrote to Sakari, I'm changing this to: We refer to this kind of control as **V4L2 device node centric** (or, simply, **vdev-centric**). I guess that this satisfies both your and Sakari's comments. > > + > > +Since the end of 2010, a new type of V4L2 device control was added in order > > +to support complex devices that are common on embedded systems. Those > > on -> for > > > +devices are controlled mainly via the media controller and sub-devices. > > +So, they're called: **media controller centric** (or, simply, > > +"**mc-centric**"). > > + > > +On **device-centric** control, the device and their corresponding hardware > > On -> For > > > +pipelines are controlled via the **V4L2 device** node. They may optionally > > +expose the hardware pipelines via the > > +:ref:`media controller API <media_controller>`. > > + > > +On a **mc-centric**, before using the V4L2 device, it is required to > > "For **mc-centric** control" > > > +set the hardware pipelines via the > > +:ref:`media controller API <media_controller>`. On those devices, the > > On -> For > > > +sub-devices' configuration can be controlled via the > > can be -> is When subdev API was added, it was optional for MC-centric devices. We used to have a bunch of such devices. Not sure if all MC-centric devices now use subdev API. That's why I used "can". > > +:ref:`sub-device API <subdev>`, with creates one device node per sub device. > > + > > +In summary, on **mc-centric** devices: > > on -> for > > > + > > +- The **V4L2 device** node is mainly responsible for controlling the > > + streaming features; > > I think "mainly" can be dropped. > > > +- The **media controller device** is responsible to setup the pipelines > > + and image settings (like size and format); > > +- The **V4L2 sub-devices** are responsible for sub-device > > + specific settings. > > + > > +.. note:: > > + > > + It is forbidden for **device-centric** devices to expose V4L2 > > + sub-devices via :ref:`sub-device API <subdev>`, although this > > + might change in the future. > > We discussed this on irc yesterday, so this has to be tweaked a bit. > > > + > > + > > +.. _v4l2_device_naming: > > > > Device Naming > > ============= > > > > Regards, > > Hans -- Thanks, Mauro
