From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from lb3-smtp-cloud7.xs4all.net ([194.109.24.31]:53268 "EHLO lb3-smtp-cloud7.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754535AbdHYKcc (ORCPT ); Fri, 25 Aug 2017 06:32:32 -0400 Subject: Re: [PATCH 1/3] media: open.rst: document devnode-centric and mc-centric types To: Mauro Carvalho Chehab , Linux Doc Mailing List , Linux Media Mailing List References: Cc: Mauro Carvalho Chehab , linux-kernel@vger.kernel.org, Jonathan Corbet From: Hans Verkuil Message-ID: <90619be1-3288-1b24-58e4-c1302133279d@xs4all.nl> Date: Fri, 25 Aug 2017 12:32:29 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-media-owner@vger.kernel.org List-ID: On 25/08/17 11:40, Mauro Carvalho Chehab wrote: > From: "mchehab@s-opensource.com" > > 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 > --- > 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 V4L2 hardware is usually complex: support for the hardware is implemented... > +often several additional drivers. The main driver always exposes one or Should we change this to "via a main (also known as 'bridge') driver"? To help understanding terminology that we use? > +more **V4L2 device** devnodes (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). They can be implicitly controlled directly by the > +main driver or explicitly through via the **V4L2 sub-device API** interface. > + > +When V4L2 was originally designed, there was only one type of device control. hardware control > +The entire device was controlled via the **V4L2 device nodes**. We refer to entire V4L2 hardware > +this kind of control as **V4L2 device node centric** (or, simply, > +**vdev-centric**). > + > +Since the end of 2010, a new type of V4L2 device control was added in order hardware control > +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, they are > +"**MC-centric**"). > + > +For **vdev-centric** control, the device and their corresponding hardware s/control/hardware control/ s/the device and their corresponding hardware pipelines are/the hardware is/ (let's keep it simple). > +pipelines are controlled via the **V4L2 device** node. They may optionally node -> node (or nodes, if there is more than one V4L2 device node) > +expose via the :ref:`media controller API `. I'd say: "support the :ref:`media controller API ` as well in order to let the application know which device nodes are available. > + > +For **MC-centric** control, before using the V4L2 device, it is required to s/control/hardware control/ s/device/hardware/ (I think. Or did you mean "device node"?) > +set the hardware pipelines via the > +:ref:`media controller API `. For those devices, the > +sub-devices' configuration can be controlled via the > +:ref:`sub-device API `, with creates one device node per sub device. s/with/which/ > + > +In summary, for **MC-centric** devices: s/devices/hardware/ > + > +- 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. > + > +.. note:: > + > + A **vdev-centric** may optionally expose V4L2 sub-devices via > + :ref:`sub-device API `. In that case, it has to implement > + the :ref:`media controller API ` as well. This note should be moved up to the vdev-centric description. It's weird now as it comes after the MC centric summary, but deals with a vdev-centric driver. > + > + > + > +.. _v4l2_device_naming: > > Device Naming > ============= > Regards, Hans