[PATCH v8 0/7] document types of hardware control for V4L2

[PATCH v8 0/7] document types of hardware control for V4L2

[Mauro Carvalho Chehab]

On Kernel 2.6.39, the omap3 driver was introduced together with a new way
to control complex V4L2 devices used on embedded systems, but this was
never documented, as the original idea were to have "soon" support for
standard apps to use it as well, via libv4l, but that didn't happen so far.

Also, it is not possible for an userspace applicatin to detect the kind of
control a device supports.

This series fill the gap, by documenting the new type of hardware
control and adding a way for userspace to detect if the device can be
used or not by an standard V4L2 application.

Notes:
====

1) For the sake of better review, this series start with the addition of a
glossary, as requested by Laurent. Please notice, however, that
the glossary there references some new captions that will only be added
by subsequent patches. So, when this series get applied, the glossary
patch should actually be merged after the patches that introduce those
new captions, in order to avoid warnings for non-existing references.

2) This series doesn't contain patches that actually use the new flag.
This will be added after such patch gets reviewed.

v8:
- Addressed Hans and Sakari's comments. Hopefully, we'll all agree
  with this one :-)
- Added :term:`foo` references at the glossary and at the first time a
  term appears inside a V4L2 section.
  I opted to not replace all occurences for a couple of reasons:
  	a) it sounded overkill to me;
	b) if we decide to change some term, there will be a lot
	   more stuff to be fixed, specially for terms in plural,
	   as a plural for :term:`device` would be
	   :term:`devices <device>`.
  Once we set this patchset into a stone, it could make sense to
  run some script that would replace every other occurrence of the
  glossary terms within Documentation/media/uapi/v4l to link to
  the glossary reference - but let's postpone this to be applied
  on a separate patchset.
  Btw, it probably makes sense to make the glossary as a general
  media book glossary - but again, this is out of topic for this
  patchset.

v7:
- Altered some nomenclature at the glossary as suggested by Hans
  and used git-filter to change it on all patches.

v6:
- Some editorial changes based on comments from Hans and Sakari.

v5:
- Added more terms to the glossary
- Adjusted some wording as proposed by Hans on a few patches
  and added his ack on others

v4:

- Addressed Hans comments for v2;
- Fixed broken references at the glossary.rst

v3:

- Add a glossary to be used by the new documentation about hardware control;
- Add a patch removing minor number range
- Use glossary terms at open.rst
- Split the notice about subdev-API on vdev-centric, as this change
   will require further discussions.

v2:

- added a patch at the beginning of the series better defining the
  device node naming rules;
- better defined the differenes between device hardware and V4L2 device node
  as suggested by Laurent and with changes proposed by Hans and Sakari
- changed the caps flag to indicate MC-centric devices
- removed the final patch that would use the new caps flag. I'll write it
  once we agree on the new caps flag.

Mauro Carvalho Chehab (7):
  media: add glossary.rst with a glossary of terms used at V4L2 spec
  media: open.rst: better document device node naming
  media: open.rst: remove the minor number range
  media: open.rst: document vdevnode-centric and mc-centric types
  media: open.rst: Adjust some terms to match the glossary
  media: videodev2: add a flag for MC-centric devices
  media: open.rst: add a notice about subdev-API on vdev-centric

 Documentation/media/uapi/v4l/glossary.rst        | 167 +++++++++++++++++++++++
 Documentation/media/uapi/v4l/open.rst            | 158 +++++++++++++++++----
 Documentation/media/uapi/v4l/v4l2.rst            |   1 +
 Documentation/media/uapi/v4l/vidioc-querycap.rst |   5 +
 Documentation/media/videodev2.h.rst.exceptions   |   1 +
 include/uapi/linux/videodev2.h                   |   2 +
 6 files changed, 309 insertions(+), 25 deletions(-)
 create mode 100644 Documentation/media/uapi/v4l/glossary.rst

-- 
2.13.6

[PATCH v8 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec

[Mauro Carvalho Chehab]

Add a glossary of terms for V4L2, as several concepts are complex
enough to cause misunderstandings.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 Documentation/media/uapi/v4l/glossary.rst | 167 ++++++++++++++++++++++++++++++
 Documentation/media/uapi/v4l/v4l2.rst     |   1 +
 2 files changed, 168 insertions(+)
 create mode 100644 Documentation/media/uapi/v4l/glossary.rst

diff --git a/Documentation/media/uapi/v4l/glossary.rst b/Documentation/media/uapi/v4l/glossary.rst
new file mode 100644
index 000000000000..a5a832b4dda5
--- /dev/null
+++ b/Documentation/media/uapi/v4l/glossary.rst
@@ -0,0 +1,167 @@
+========
+Glossary
+========
+
+.. note::
+
+   This goal of section is to standardize the terms used within the V4L2
+   documentation. It is written incrementally as they are standardized in
+   the V4L2 documentation. So, it is a Work In Progress.
+
+.. Please keep the glossary entries in alphabetical order
+
+.. glossary::
+
+    Bridge driver
+	A driver that provides a bridge between the CPU's bus to the
+	data and control buses of a :term:`media hardware`. Often, the
+	bridge driver is the same as :term:`V4L2 main driver`.
+
+    Chip
+	:See: :term:`Integrated circuit`.
+
+    Device Driver
+    Driver
+	The part of the Linux Kernel that implements support
+	for a :term:`hardware component`.
+
+    Device Node
+	A character device node in the file system used to control and/or
+	do input/output data transfers from/to a Kernel driver.
+
+    Digital Signal Processor
+    DSP
+	A specialized :term:`microprocessor`, with its architecture optimized
+	for the operational requirements of digital signal processing.
+
+    Field-programmable Gate Array
+    FPGA
+	A field-programmable gate array (FPGA) is an :term:`integrated circuit`
+	designed to be configured by a customer or a designer after
+	manufacturing.
+
+	:See: https://en.wikipedia.org/wiki/Field-programmable_gate_array.
+
+    Hardware component
+	A subset of the :term:`media hardware`. For example an :term:`I²C`
+	or :term:`SPI` device, or an :term:`IP block` inside an
+	:term:`SoC` or :term:`FPGA`.
+
+    Image Signal Processor
+    ISP
+	A specialized :term:`microprocessor` that implements a set of
+	algorithms for processing image data. ISPs may implement algorithms
+	for lens shading correction, demosaic, scaling and pixel format
+	conversion as well as produce statistics for the use of the control
+	algorithms (e.g. automatic exposure, white balance and focus).
+
+	ISP drivers often contain a receiver for image data from external
+	sources such as sensors and act as :term:`V4L2 main driver`.
+
+    Integrated circuit
+    IC
+	A set of electronic circuits on one small flat piece of
+	semiconductor material, normally silicon.
+
+	Also known as :term:`chip`.
+
+    Intellectual property core
+    IP core
+	In electronic design a semiconductor intellectual property core,
+	is a reusable unit of logic, cell, or integrated circuit layout
+	design that is the intellectual property of one party.
+	IP cores may be licensed to another party or can be owned
+	and used by a single party alone.
+
+	:See: https://en.wikipedia.org/wiki/Semiconductor_intellectual_property_core).
+
+    Inter-Integrated Circuit
+    I²C
+	A  multi-master, multi-slave, packet switched, single-ended,
+	serial computer bus. A :term:`V4L2 sub-device driver` usually is
+	controlled via this bus.
+
+	:See: http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
+
+    IP block
+	:See: :term:`IP core`.
+
+    Media controller
+    MC
+	An API designed to expose and control the relationships of the
+	:term:`media hardware` to applications.
+
+	:See: :ref:`media_controller`.
+
+    Media controller centric
+    MC-centric
+	:term:`V4L2 hardware` that requires a :term:`media controller`.
+
+	:See: :ref:`v4l2_hardware_control`.
+
+    Media hardware
+	A group of hardware components that together form the
+	functional media hardware. For instance the :term:`SoC`
+	:term:`ISP` :term:`IP cores <ip core>` and external camera
+	sensors together form the camera media hardware.
+
+    Media hardware control
+	Type of control for a :term:`media hardware` supported a
+	V4L2 :term:`driver`.
+
+	:See: :ref:`v4l2_hardware_control`.
+
+    Microprocessor
+	An electronic circuitry that carries out the instructions
+	of a computer program by performing the basic arithmetic, logical,
+	control and input/output (I/O) operations specified by the
+	instructions on a single :term:`integrated circuit`.
+
+    SMBus
+	A subset of :term:`I²C`, with defines a stricter usage of the bus.
+
+    Serial Peripheral Interface
+    SPI
+	Synchronous serial communication interface specification used for
+	short distance communication, primarily in embedded systems.
+
+    System on a Chip
+    SoC
+	An :term:`integrated circuit` that integrates all components of a
+	computer or other electronic systems.
+
+    V4L2 device node
+	A :term:`device node` that is associated to a
+	:term:`V4L2 main driver`, as specified in :ref:`v4l2_device_naming`.
+
+    V4L2 hardware
+	Hardware that is controlled by a :term:`V4L2 main driver` or a
+	:term:`V4L2 sub-device driver`. V4L2 hardware is a subset of the
+	:term:`media hardware`. Often the two are the same, but
+	:term:`media hardware` can also contain other non-V4L2 hardware
+	such as Digital TV hardware.
+
+    V4L2 main driver
+	The V4L2 :term:`device driver` that implements the main logic to
+	talk with the :term:`V4L2 hardware`.
+
+	Often, the same as :term:`bridge driver`.
+
+	:See: :ref:`v4l2_hardware_control`.
+
+    V4L2 sub-device
+	:See: :term:`V4L2 sub-device driver`.
+
+    V4L2 sub-device driver
+	A :term:`driver` for a :term:`media hardware` whose bus(es)
+	connects it to the hardware controlled via the
+	:term:`V4L2 main driver`.
+
+	:See: :ref:`subdev`.
+
+    Video device node centric
+    Vdevnode-centric
+	:term:`V4L2 hardware` that is controlled via
+	:term:`V4L2 device nodes <v4l2 device node>`.
+
+	:See: :ref:`v4l2_hardware_control`.
diff --git a/Documentation/media/uapi/v4l/v4l2.rst b/Documentation/media/uapi/v4l/v4l2.rst
index 2128717299b3..698c060939f0 100644
--- a/Documentation/media/uapi/v4l/v4l2.rst
+++ b/Documentation/media/uapi/v4l/v4l2.rst
@@ -32,6 +32,7 @@ This part describes the Video for Linux API version 2 (V4L2 API) specification.
     videodev
     capture-example
     v4l2grab-example
+    glossary
     biblio
 
 
-- 
2.13.6

[PATCH v8 2/7] media: open.rst: better document device node naming

[Mauro Carvalho Chehab]

Right now, only kAPI documentation describes the device naming.
However, such description is needed at the uAPI too. Add it,
and describe how to get an unique identify for a given device.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 Documentation/media/uapi/v4l/open.rst | 53 ++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 7 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index afd116edb40d..de2144277f55 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,14 +7,16 @@ Opening and Closing Devices
 ***************************
 
 
-Device Naming
-=============
+.. _v4l2_device_naming:
 
-V4L2 drivers are implemented as kernel modules, loaded manually by the
-system administrator or automatically when a device is first discovered.
-The driver modules plug into the "videodev" kernel module. It provides
-helper functions and a common application interface specified in this
-document.
+V4L2 Device Node Naming
+=======================
+
+V4L2 :term:`drivers <driver>` are implemented as kernel modules, loaded
+manually by the system administrator or automatically when a device is
+first discovered. The driver modules plug into the ``videodev`` kernel
+module. It provides helper functions and a common application interface
+specified in this document.
 
 Each driver thus loaded registers one or more device nodes with major
 number 81 and a minor number between 0 and 255. Minor numbers are
@@ -23,6 +25,43 @@ option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers
 are allocated in ranges depending on the device node type (video, radio,
 etc.).
 
+The existing :term:`device node` types defined at V4L2 spec are:
+
+======================== ======================================================
+Default device node name Usage
+======================== ======================================================
+``/dev/videoX``		 Video input/output devices
+``/dev/vbiX``		 Vertical blank data (i.e. closed captions, teletext)
+``/dev/radioX``		 Radio tuners and modulators
+``/dev/swradioX``	 Software Defined Radio tuners and modulators
+``/dev/v4l-touchX``	 Touch sensors
+======================== ======================================================
+
+Where ``X`` is a non-negative number.
+
+.. note::
+
+   1. The actual device node name is system-dependent, as udev rules may apply.
+   2. There is no guarantee that ``X`` will remain the same for the same
+      device, as the number depends on the device driver's probe order.
+      If you need an unique name, udev default rules produce
+      ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` directories containing
+      links that can be used uniquely to identify a V4L2 device node::
+
+	$ tree /dev/v4l
+	/dev/v4l
+	??? by-id
+	?   ??? usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0
+	??? by-path
+	    ??? pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video0
+
+   3. :term:`V4L2 sub-device` nodes (e. g. ``/dev/v4l-sudevX``) provide a
+      different API and aren't considered as
+      :term:`V4L2 device nodes <v4l2 device node>`.
+
+      They are covered at :ref:`subdev`.
+
+
 Many drivers support "video_nr", "radio_nr" or "vbi_nr" module
 options to select specific video/radio/vbi node numbers. This allows the
 user to request that the device node is named e.g. /dev/video5 instead
-- 
2.13.6

[PATCH v8 3/7] media: open.rst: remove the minor number range

[Mauro Carvalho Chehab]

minor numbers use to range between 0 to 255, but that
was changed a long time ago. While it still applies when
CONFIG_VIDEO_FIXED_MINOR_RANGES, when the minor number is
dynamically allocated, this may not be true. In any case,
this is not relevant, as udev will take care of it.

So, remove this useless misinformation.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 Documentation/media/uapi/v4l/open.rst | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index de2144277f55..46ef63e05696 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -19,11 +19,10 @@ module. It provides helper functions and a common application interface
 specified in this document.
 
 Each driver thus loaded registers one or more device nodes with major
-number 81 and a minor number between 0 and 255. Minor numbers are
-allocated dynamically unless the kernel is compiled with the kernel
-option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers
-are allocated in ranges depending on the device node type (video, radio,
-etc.).
+number 81. Minor numbers are allocated dynamically unless the kernel
+is compiled with the kernel option CONFIG_VIDEO_FIXED_MINOR_RANGES.
+In that case minor numbers are allocated in ranges depending on the
+device node type.
 
 The existing :term:`device node` types defined at V4L2 spec are:
 
-- 
2.13.6

[PATCH v8 4/7] media: open.rst: document vdevnode-centric and mc-centric types

[Mauro Carvalho Chehab]

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@s-opensource.com>
---
 Documentation/media/uapi/v4l/open.rst | 55 +++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 46ef63e05696..1a8a9e1d0e84 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,6 +7,61 @@ Opening and Closing Devices
 ***************************
 
 
+.. _v4l2_hardware_control:
+
+
+Types of V4L2 media hardware control
+====================================
+
+A :term:`V4L2 hardware` is usually complex: support for it is
+implemented via a :term:`V4L2 main driver` and often by several
+additional :term:`drivers <driver>`.
+The main driver always exposes one or more
+:term:`V4L2 device nodes <v4l2 device node>`
+(see :ref:`v4l2_device_naming`) with are responsible for implementing
+data streaming, if applicable.
+
+The other drivers are called :term:`V4L2 sub-devices <v4l2 sub-device>`
+and provide control to other
+:term:`hardware components <hardware component>` are usually connected
+via a serial bus (like :term:`I²C`, :term:`SMBus` or :term:`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, the
+:term:`V4L2 device nodes <v4l2 device node>` served the purpose of both
+control and data interfaces and there was no separation
+between the two interface-wise. V4L2 controls, setting inputs and outputs,
+format configuration and buffer related operations were all performed
+through the same **V4L2 device nodes**. Devices offering such interface are
+called **V4L2 device node centric**.
+
+Later on, support for the :term:`media controller` interface was added
+to V4L2 in order to better support complex :term:`V4L2 hardware` where the
+**V4L2** interface alone could no longer meaningfully serve as both a
+control and a data interface. On such V4L2 hardware, **V4L2** interface
+remains a data interface whereas control takes place through the
+:term:`media controller` and :term:`V4L2 sub-device` interfaces. Stream
+control is an exception to this: streaming is enabled and disabled
+through the **V4L2** interface. These devices are called
+**Media controller centric**.
+
+**MC-centric** V4L2 hardware provide more versatile control of the
+hardware than **V4L2 device node centric** devices at the expense of
+requiring device-specific userspace settings.
+
+On **MC-centric** V4L2 hardware, the **V4L2 sub-device nodes**
+represent specific parts of the V4L2 hardware, to which they enable
+control.
+
+Also, the additional versatility of **MC-centric** V4L2 hardware comes
+with additional responsibilities, the main one of which is the requirements
+of the user configuring the device pipeline before starting streaming. This
+typically involves configuring the links using the **Media controller**
+interface and the media bus formats on pads (at both ends of the links)
+using the **V4L2 sub-device** interface.
+
 .. _v4l2_device_naming:
 
 V4L2 Device Node Naming
-- 
2.13.6

[PATCH v8 5/7] media: open.rst: Adjust some terms to match the glossary

[Mauro Carvalho Chehab]

As we now have a glossary, some terms used on open.rst
require adjustments.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 Documentation/media/uapi/v4l/open.rst | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 1a8a9e1d0e84..c9e6bc9280a6 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -159,27 +159,28 @@ Related Devices
 Devices can support several functions. For example video capturing, VBI
 capturing and radio support.
 
-The V4L2 API creates different nodes for each of these functions.
+The V4L2 API creates different :term:`V4L2 device nodes <v4l2 device node>`
+types for each of these functions.
 
-The V4L2 API was designed with the idea that one device node could
+The V4L2 API was designed with the idea that one :term:`device node` could
 support all functions. However, in practice this never worked: this
-'feature' was never used by applications and many drivers did not
-support it and if they did it was certainly never tested. In addition,
+'feature' was never used by applications and many :term:`drivers <driver>`
+did not support it and if they did it was certainly never tested. In addition,
 switching a device node between different functions only works when
 using the streaming I/O API, not with the
 :ref:`read() <func-read>`/\ :ref:`write() <func-write>` API.
 
-Today each device node supports just one function.
+Today each V4L2 device node supports just one function.
 
-Besides video input or output the hardware may also support audio
-sampling or playback. If so, these functions are implemented as ALSA PCM
-devices with optional ALSA audio mixer devices.
+Besides video input or output, the :term:`media hardware` may also support
+audio sampling or playback. If so, these functions are implemented as ALSA
+PCM devices with optional ALSA audio mixer devices.
 
 One problem with all these devices is that the V4L2 API makes no
-provisions to find these related devices. Some really complex devices
-use the Media Controller (see :ref:`media_controller`) which can be
-used for this purpose. But most drivers do not use it, and while some
-code exists that uses sysfs to discover related devices (see
+provisions to find these related V4L2 device nodes. Some really complex
+hardware use the :term:`media controller` (see :ref:`media_controller`) which
+can be used for this purpose. But several drivers do not use it, and while
+some code exists that uses sysfs to discover related V4L2 device nodes (see
 libmedia_dev in the
 `v4l-utils <http://git.linuxtv.org/cgit.cgi/v4l-utils.git/>`__ git
 repository), there is no library yet that can provide a single API
-- 
2.13.6

[PATCH v8 6/7] media: videodev2: add a flag for MC-centric devices

[Mauro Carvalho Chehab]

As both vdev-centric and MC-centric devices may implement the
same APIs, we need a flag to allow userspace to distinguish
between them.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 Documentation/media/uapi/v4l/open.rst            | 7 +++++++
 Documentation/media/uapi/v4l/vidioc-querycap.rst | 5 +++++
 Documentation/media/videodev2.h.rst.exceptions   | 1 +
 include/uapi/linux/videodev2.h                   | 2 ++
 4 files changed, 15 insertions(+)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index c9e6bc9280a6..58ab75959584 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -62,6 +62,13 @@ typically involves configuring the links using the **Media controller**
 interface and the media bus formats on pads (at both ends of the links)
 using the **V4L2 sub-device** interface.
 
+.. attention::
+
+   Devices that require **MC-centric** media hardware control should
+   report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
+   (see :ref:`VIDIOC_QUERYCAP`).
+
+
 .. _v4l2_device_naming:
 
 V4L2 Device Node Naming
diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst
index 66fb1b3d6e6e..944bc5ba484f 100644
--- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
+++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
@@ -254,6 +254,11 @@ specification the ioctl returns an ``EINVAL`` error code.
     * - ``V4L2_CAP_TOUCH``
       - 0x10000000
       - This is a touch device.
+    * - ``V4L2_MC_CENTRIC``
+      - 0x20000000
+      - Indicates that the device require **MC-centric** hardware
+        control, and thus can't be used by **vdevnode-centric** applications.
+        See :ref:`v4l2_hardware_control` for more details.
     * - ``V4L2_CAP_DEVICE_CAPS``
       - 0x80000000
       - The driver fills the ``device_caps`` field. This capability can
diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
index a5cb0a8686ac..b51a575f9f75 100644
--- a/Documentation/media/videodev2.h.rst.exceptions
+++ b/Documentation/media/videodev2.h.rst.exceptions
@@ -157,6 +157,7 @@ replace define V4L2_CAP_META_CAPTURE device-capabilities
 replace define V4L2_CAP_READWRITE device-capabilities
 replace define V4L2_CAP_ASYNCIO device-capabilities
 replace define V4L2_CAP_STREAMING device-capabilities
+replace define V4L2_CAP_MC_CENTRIC device-capabilities
 replace define V4L2_CAP_DEVICE_CAPS device-capabilities
 replace define V4L2_CAP_TOUCH device-capabilities
 
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 185d6a0acc06..4ff1224719a7 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -460,6 +460,8 @@ struct v4l2_capability {
 
 #define V4L2_CAP_TOUCH                  0x10000000  /* Is a touch device */
 
+#define V4L2_CAP_MC_CENTRIC             0x20000000  /* Device require MC-centric hardware control */
+
 #define V4L2_CAP_DEVICE_CAPS            0x80000000  /* sets device capabilities field */
 
 /*
-- 
2.13.6

[PATCH v8 7/7] media: open.rst: add a notice about subdev-API on vdev-centric

[Mauro Carvalho Chehab]

The documentation doesn't mention if vdev-centric hardware
control would have subdev API or not.

Add a notice about that, reflecting the current status, where
three drivers use it, in order to support some subdev-specific
controls.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 Documentation/media/uapi/v4l/open.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 58ab75959584..ccdf53ab347c 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -62,6 +62,13 @@ typically involves configuring the links using the **Media controller**
 interface and the media bus formats on pads (at both ends of the links)
 using the **V4L2 sub-device** interface.
 
+.. note::
+
+   A **vdevnode-centric** may also 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.
+
+
 .. attention::
 
    Devices that require **MC-centric** media hardware control should
-- 
2.13.6

Re: [PATCH v8 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec

[Hans Verkuil]

More (mostly) small stuff:

On 10/10/2017 01:45 PM, Mauro Carvalho Chehab wrote:
> Add a glossary of terms for V4L2, as several concepts are complex
> enough to cause misunderstandings.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> ---
>  Documentation/media/uapi/v4l/glossary.rst | 167 ++++++++++++++++++++++++++++++
>  Documentation/media/uapi/v4l/v4l2.rst     |   1 +
>  2 files changed, 168 insertions(+)
>  create mode 100644 Documentation/media/uapi/v4l/glossary.rst
> 
> diff --git a/Documentation/media/uapi/v4l/glossary.rst b/Documentation/media/uapi/v4l/glossary.rst
> new file mode 100644
> index 000000000000..a5a832b4dda5
> --- /dev/null
> +++ b/Documentation/media/uapi/v4l/glossary.rst
> @@ -0,0 +1,167 @@
> +========
> +Glossary
> +========
> +
> +.. note::
> +
> +   This goal of section is to standardize the terms used within the V4L2
> +   documentation. It is written incrementally as they are standardized in
> +   the V4L2 documentation. So, it is a Work In Progress.
> +
> +.. Please keep the glossary entries in alphabetical order
> +
> +.. glossary::
> +
> +    Bridge driver
> +	A driver that provides a bridge between the CPU's bus to the
> +	data and control buses of a :term:`media hardware`. Often, the
> +	bridge driver is the same as :term:`V4L2 main driver`.
> +
> +    Chip
> +	:See: :term:`Integrated circuit`.
> +
> +    Device Driver
> +    Driver
> +	The part of the Linux Kernel that implements support
> +	for a :term:`hardware component`.
> +
> +    Device Node
> +	A character device node in the file system used to control and/or
> +	do input/output data transfers from/to a Kernel driver.
> +
> +    Digital Signal Processor
> +    DSP
> +	A specialized :term:`microprocessor`, with its architecture optimized
> +	for the operational requirements of digital signal processing.
> +
> +    Field-programmable Gate Array
> +    FPGA
> +	A field-programmable gate array (FPGA) is an :term:`integrated circuit`
> +	designed to be configured by a customer or a designer after
> +	manufacturing.
> +
> +	:See: https://en.wikipedia.org/wiki/Field-programmable_gate_array.
> +
> +    Hardware component
> +	A subset of the :term:`media hardware`. For example an :term:`I²C`
> +	or :term:`SPI` device, or an :term:`IP block` inside an
> +	:term:`SoC` or :term:`FPGA`.
> +
> +    Image Signal Processor
> +    ISP
> +	A specialized :term:`microprocessor` that implements a set of
> +	algorithms for processing image data. ISPs may implement algorithms
> +	for lens shading correction, demosaic, scaling and pixel format
> +	conversion as well as produce statistics for the use of the control
> +	algorithms (e.g. automatic exposure, white balance and focus).
> +
> +	ISP drivers often contain a receiver for image data from external
> +	sources such as sensors and act as :term:`V4L2 main driver`.
> +
> +    Integrated circuit
> +    IC
> +	A set of electronic circuits on one small flat piece of
> +	semiconductor material, normally silicon.
> +
> +	Also known as :term:`chip`.
> +
> +    Intellectual property core
> +    IP core
> +	In electronic design a semiconductor intellectual property core,
> +	is a reusable unit of logic, cell, or integrated circuit layout
> +	design that is the intellectual property of one party.
> +	IP cores may be licensed to another party or can be owned
> +	and used by a single party alone.
> +
> +	:See: https://en.wikipedia.org/wiki/Semiconductor_intellectual_property_core).
> +
> +    Inter-Integrated Circuit
> +    I²C
> +	A  multi-master, multi-slave, packet switched, single-ended,
> +	serial computer bus. A :term:`V4L2 sub-device driver` usually is
> +	controlled via this bus.
> +
> +	:See: http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> +
> +    IP block
> +	:See: :term:`IP core`.
> +
> +    Media controller
> +    MC
> +	An API designed to expose and control the relationships of the
> +	:term:`media hardware` to applications.
> +
> +	:See: :ref:`media_controller`.
> +
> +    Media controller centric
> +    MC-centric
> +	:term:`V4L2 hardware` that requires a :term:`media controller`.
> +
> +	:See: :ref:`v4l2_hardware_control`.
> +
> +    Media hardware
> +	A group of hardware components that together form the
> +	functional media hardware. For instance the :term:`SoC`
> +	:term:`ISP` :term:`IP cores <ip core>` and external camera
> +	sensors together form the camera media hardware.

Perhaps this is a bit better:

	...form the media hardware for a camera.

> +
> +    Media hardware control
> +	Type of control for a :term:`media hardware` supported a

for a -> for
supported -> supported by

> +	V4L2 :term:`driver`.
> +
> +	:See: :ref:`v4l2_hardware_control`.

Do we actually need this term in the glossary? I'm not convinced. We will
typically talk about 'MC-centric' or 'Video device node centric', but rarely
about 'Media hardware control'. Just my opinion though.

> +
> +    Microprocessor
> +	An electronic circuitry that carries out the instructions

It's either "Electronic circuitry" or "An electronic circuit". In this case
I'd say the former, but I'm no HW engineer.

> +	of a computer program by performing the basic arithmetic, logical,
> +	control and input/output (I/O) operations specified by the
> +	instructions on a single :term:`integrated circuit`.
> +
> +    SMBus
> +	A subset of :term:`I²C`, with defines a stricter usage of the bus.

with -> which

> +
> +    Serial Peripheral Interface
> +    SPI
> +	Synchronous serial communication interface specification used for
> +	short distance communication, primarily in embedded systems.

...primarily used in...

> +
> +    System on a Chip
> +    SoC
> +	An :term:`integrated circuit` that integrates all components of a
> +	computer or other electronic systems.
> +
> +    V4L2 device node
> +	A :term:`device node` that is associated to a
> +	:term:`V4L2 main driver`, as specified in :ref:`v4l2_device_naming`.
> +
> +    V4L2 hardware
> +	Hardware that is controlled by a :term:`V4L2 main driver` or a
> +	:term:`V4L2 sub-device driver`. V4L2 hardware is a subset of the
> +	:term:`media hardware`. Often the two are the same, but
> +	:term:`media hardware` can also contain other non-V4L2 hardware
> +	such as Digital TV hardware.
> +
> +    V4L2 main driver
> +	The V4L2 :term:`device driver` that implements the main logic to
> +	talk with the :term:`V4L2 hardware`.
> +
> +	Often, the same as :term:`bridge driver`.

Remove the comma after 'Often'.

> +
> +	:See: :ref:`v4l2_hardware_control`.
> +
> +    V4L2 sub-device
> +	:See: :term:`V4L2 sub-device driver`.

Isn't a "V4L2 sub-device" typically an instance of a device as implemented by
a "V4L2 sub-device driver"?

> +
> +    V4L2 sub-device driver
> +	A :term:`driver` for a :term:`media hardware` whose bus(es)

Not media hardware, but "hardware component".

> +	connects it to the hardware controlled via the

I think 'by' is better than 'via'.

> +	:term:`V4L2 main driver`.
> +
> +	:See: :ref:`subdev`.
> +
> +    Video device node centric
> +    Vdevnode-centric
> +	:term:`V4L2 hardware` that is controlled via

Same as before: I think 'by' is better than 'via'.

> +	:term:`V4L2 device nodes <v4l2 device node>`.
> +
> +	:See: :ref:`v4l2_hardware_control`.
> diff --git a/Documentation/media/uapi/v4l/v4l2.rst b/Documentation/media/uapi/v4l/v4l2.rst
> index 2128717299b3..698c060939f0 100644
> --- a/Documentation/media/uapi/v4l/v4l2.rst
> +++ b/Documentation/media/uapi/v4l/v4l2.rst
> @@ -32,6 +32,7 @@ This part describes the Video for Linux API version 2 (V4L2 API) specification.
>      videodev
>      capture-example
>      v4l2grab-example
> +    glossary
>      biblio
>  
>  
> 

Regards,

	Hans

Re: [PATCH v8 4/7] media: open.rst: document vdevnode-centric and mc-centric types

[Hans Verkuil]

More word-smithing...

On 10/10/2017 01:45 PM, 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@s-opensource.com>
> ---
>  Documentation/media/uapi/v4l/open.rst | 55 +++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> index 46ef63e05696..1a8a9e1d0e84 100644
> --- a/Documentation/media/uapi/v4l/open.rst
> +++ b/Documentation/media/uapi/v4l/open.rst
> @@ -7,6 +7,61 @@ Opening and Closing Devices
>  ***************************
>  
>  
> +.. _v4l2_hardware_control:
> +
> +
> +Types of V4L2 media hardware control
> +====================================
> +
> +A :term:`V4L2 hardware` is usually complex: support for it is

No 'A '.

> +implemented via a :term:`V4L2 main driver` and often by several

I prefer 'by' instead of 'via'.

> +additional :term:`drivers <driver>`.
> +The main driver always exposes one or more
> +:term:`V4L2 device nodes <v4l2 device node>`
> +(see :ref:`v4l2_device_naming`) with are responsible for implementing

with -> which

> +data streaming, if applicable.
> +
> +The other drivers are called :term:`V4L2 sub-devices <v4l2 sub-device>`

I'd say "V4L2 sub-device drivers"

> +and provide control to other
> +:term:`hardware components <hardware component>` are usually connected

:term:`hardware components <hardware component>`. Those component are usually controlled

> +via a serial bus (like :term:`I²C`, :term:`SMBus` or :term:`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, the
> +:term:`V4L2 device nodes <v4l2 device node>` served the purpose of both
> +control and data interfaces and there was no separation
> +between the two interface-wise. V4L2 controls, setting inputs and outputs,

Instead of 'interface-wise' I'd use 'API-wise'. That reminds me: should we add
'API' to the glossary as well? (Can be done later)

> +format configuration and buffer related operations were all performed
> +through the same **V4L2 device nodes**. Devices offering such interface are
> +called **V4L2 device node centric**.
> +
> +Later on, support for the :term:`media controller` interface was added
> +to V4L2 in order to better support complex :term:`V4L2 hardware` where the
> +**V4L2** interface alone could no longer meaningfully serve as both a
> +control and a data interface. On such V4L2 hardware, **V4L2** interface

**V4L2** -> the **V4L2**

> +remains a data interface whereas control takes place through the
> +:term:`media controller` and :term:`V4L2 sub-device` interfaces. Stream
> +control is an exception to this: streaming is enabled and disabled
> +through the **V4L2** interface. These devices are called
> +**Media controller centric**.
> +
> +**MC-centric** V4L2 hardware provide more versatile control of the

provide -> provides

> +hardware than **V4L2 device node centric** devices at the expense of
> +requiring device-specific userspace settings.
> +
> +On **MC-centric** V4L2 hardware, the **V4L2 sub-device nodes**
> +represent specific parts of the V4L2 hardware, to which they enable
> +control.

I'd rephrase this:

On **MC-centric** V4L2 hardware, the **V4L2 sub-device nodes**
provide control of the specific part of the V4L2 hardware represented
by each node.

> +
> +Also, the additional versatility of **MC-centric** V4L2 hardware comes
> +with additional responsibilities, the main one of which is the requirements

...of which the main one is the requirement...

> +of the user configuring the device pipeline before starting streaming. This
> +typically involves configuring the links using the **Media controller**
> +interface and the media bus formats on pads (at both ends of the links)
> +using the **V4L2 sub-device** interface.
> +
>  .. _v4l2_device_naming:
>  
>  V4L2 Device Node Naming
> 

Regards,

	Hans