Em Mon, 28 Aug 2017 11:36:13 +0200 Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > On 26/08/17 13:53, Mauro Carvalho Chehab wrote: > > 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 have never clearly documented in the V4L2 specification > > the differences between the two types. > > > > Let's document them based on the the current implementation. > > > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> > > --- > > Documentation/media/uapi/v4l/open.rst | 49 +++++++++++++++++++++++++++++++++++ > > 1 file changed, 49 insertions(+) > > > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > > index 96ac972c1fa2..51acb8de8ba8 100644 > > --- a/Documentation/media/uapi/v4l/open.rst > > +++ b/Documentation/media/uapi/v4l/open.rst > > @@ -7,6 +7,55 @@ Opening and Closing Devices > > *************************** > > > > > > +.. _v4l2_hardware_control: > > + > > + > > +Types of V4L2 hardware peripheral control > > +========================================= > > + > > +V4L2 hardware periferal is usually complex: support for it is > > peripheral > > I *really* don't like the term "hardware peripheral". For me that means a > mouse, keyboard, printer, webcam, i.e. some external device that you connect > to a USB bus or similar, but it makes no sense as a definition of an > SoC + sensor(s) hardware design. > > I would simple define "V4L2 hardware" as consisting of 1 or more "V4L2 hardware > components". I don't have a strong preference here. If I remember my computer architecture books, back on the old days, everything that does I/O is technically a peripheral to the CPU. That seems, btw, the definition used by Wikipedia: https://en.wikipedia.org/wiki/Peripheral So, calling it as peripheral works. On the other hand, "V4L2 hardware" doesn't seem an adequate term, as it associates a software API with a piece of hardware. It is weirder when the hardware have an hybrid tuner, as the same hardware is visible via both DVB and V4L2 APIs. Yet, we could find a similar wording, like "media hardware". I'm OK to replace it to something like "media hardware", but, I prefer to do such change on a patch to be applied after this series, in order to minimize the rebase needs[1]. [1] as you noticed on patch 6/7, with all those nomenclature changes, one of the places were written as "v4l2-centric" instead of "vdev-centric" as on the other patches. That's basically the problem with rebases: we end by letting loose ends. So, IMHO, if we end by deciding to rename A->B C->D Let's do it on a separate patch at the end of the series, as a simple grep |sed -i could replace all occurrences at once without letting lose ands and without needing to solve patch merge conflicts. > > +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`). > > I think we should mention that the V4L2 device nodes are responsible for > implementing streaming (if applicable) of data. Ok. > > + > > +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 > > +peripheral control: via the **V4L2 device nodes**. We refer to this kind > > Again, I prefer the term "V4L2 hardware control". > > > +of control as **V4L2 device node centric** (or, simply, "**vdev-centric**"). > > + > > +Later (kernel 2.6.39), a new type of periferal control was > > periferal -> V4L2 hardware > > > +added in order to support complex peripherals that are common for embedded > > complex V4L2 hardware > > (repeat below where you use this 'peripheral' term) > > > +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**"). > > add 'control' at the end. Ok. > > + > > +For **vdev-centric** hardware peripheral control, the peripheral 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 which device nodes are available > > to know -> know > > Actually, I would rephrase this to: > > in order to inform the application which device nodes are available Ok. > > +(see :ref:`related`). > > + > > +For **MC-centric** hardware peripheral 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. > > + > > +In summary, for **MC-centric** hardware peripheral control: > > + > > +- The **V4L2 device** node is responsible for controlling the streaming > > + features; > > +- The **media controller device** is responsible to setup the pipelines > > + at the peripheral; > > +- The **V4L2 sub-devices** are responsible for V4L2 sub-device > > + specific settings at the sub-device hardware components. > > ... settings of the corresponding hardware components. > > I agree with Laurent that I don't think this summary is needed. I would drop > it for v5 and we can look at the text again and see if it needs more work to > clarify things. Ok, I'll drop it. > The main thing here is that the note about the V4L2 device node being responsible > for controlling the streaming features is mentioned when the V4L2 device node is > introduced above, since this is true for both MC and vdev-centric HW control. > > > + > > + > > .. _v4l2_device_naming: > > > > V4L2 Device Node Naming > > > > Regards, > > Hans I'll submit a v5 soon, without the terms renaming. If we all agree with renaming terms, I'll produce a separate patch fixing it where used. Thanks, Mauro
