[PATCH v6 0/7] document types of hardware control for V4L2

[PATCH v6 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.

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 devnode-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        | 150 +++++++++++++++++++++++
 Documentation/media/uapi/v4l/open.rst            | 119 +++++++++++++++---
 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, 264 insertions(+), 14 deletions(-)
 create mode 100644 Documentation/media/uapi/v4l/glossary.rst

-- 
2.13.5

[PATCH v6 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 | 150 ++++++++++++++++++++++++++++++
 Documentation/media/uapi/v4l/v4l2.rst     |   1 +
 2 files changed, 151 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..afafe1bc1894
--- /dev/null
+++ b/Documentation/media/uapi/v4l/glossary.rst
@@ -0,0 +1,150 @@
+========
+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
+	The same as V4L2 main driver.
+
+    Device Node
+	A character device node in the file system used to control and do
+	input/output data transfers from/to a Kernel driver.
+
+    Digital Signal Processor - DSP
+	A specialized microprocessor, with its architecture optimized for
+	the operational needs of digital signal processing.
+
+    Driver
+	The part of the Linux Kernel that implements support
+	for a hardware component.
+
+    Field-programmable Gate Array - FPGA
+	A field-programmable gate array (FPGA) is an 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 media hardware. For example an I²C or SPI device,
+	or an IP block inside an SoC or FPGA.
+
+    Hardware peripheral
+	A group of hardware components that together make a larger
+	user-facing functional peripheral. For instance the SoC ISP IP
+	cores and external camera sensors together make a
+	camera hardware peripheral.
+
+	Also known as peripheral.
+
+    Hardware peripheral control
+	Type of control for a hardware peripheral supported by V4L2 drivers.
+
+	See :ref:`v4l2_hardware_control`.
+
+    Inter-Integrated Circuit - I²C
+	A  multi-master, multi-slave, packet switched, single-ended,
+	serial computer bus used to control V4L2 sub-devices.
+
+	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
+
+    Integrated circuit - IC
+	A set of electronic circuits on one small flat piece of
+	semiconductor material, normally silicon.
+
+	Also known as chip.
+
+    IP block
+	The same as IP core.
+
+    Intelectual 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).
+
+    Image Signal Processor - ISP
+	A specialised processor 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).
+
+    Peripheral
+	The same as hardware peripheral.
+
+    Media Controller
+	An API designed to expose and control devices and sub-devices
+	relationships to applications.
+
+	See :ref:`media_controller`.
+
+    MC-centric
+	V4L2 hardware that requires a Media controller.
+
+	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 integrated circuit.
+
+    SMBus
+	A subset of I²C, with defines a stricter usage of the bus.
+
+    Serial Peripheral Interface Bus - SPI
+	Synchronous serial communication interface specification used for
+	short distance communication, primarily in embedded systems.
+
+    System on a Chip - SoC
+	An integrated circuit that integrates all components of a computer
+	or other electronic systems.
+
+    Sub-device hardware components
+	Hardware components that aren't controlled by the
+	V4L2 main driver.
+
+    V4L2 device node
+	A device node that is associated to a V4L2 main driver,
+	as specified in :ref:`v4l2_device_naming`.
+
+    V4L2 hardware
+	A hardware used to on a media device supported by the V4L2
+	subsystem.
+
+    V4L2 hardware control
+	The type of hardware control that a device supports.
+
+	See :ref:`v4l2_hardware_control`.
+
+    V4L2 main driver
+	The V4L2 device driver that implements the main logic to talk with
+	the V4L2 hardware.
+
+	Also known as bridge driver.
+
+	See :ref:`v4l2_hardware_control`.
+
+    V4L2 sub-device
+	Part of the media hardware that it is implemented by a device
+	driver that is not part of the main V4L2 driver.
+
+	See :ref:`subdev`.
+
+    Vdev-centric
+	V4L2 hardware that it is controlled via V4L2 device nodes.
+
+	See :ref:`v4l2_hardware_control`.
diff --git a/Documentation/media/uapi/v4l/v4l2.rst b/Documentation/media/uapi/v4l/v4l2.rst
index f52a11c949d3..1ee4b86d18e1 100644
--- a/Documentation/media/uapi/v4l/v4l2.rst
+++ b/Documentation/media/uapi/v4l/v4l2.rst
@@ -31,6 +31,7 @@ This part describes the Video for Linux API version 2 (V4L2 API) specification.
     videodev
     capture-example
     v4l2grab-example
+    glossary
     biblio
 
 
-- 
2.13.5

[PATCH v6 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.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 Documentation/media/uapi/v4l/open.rst | 44 ++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index afd116edb40d..7e7aad784388 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,12 +7,14 @@ Opening and Closing Devices
 ***************************
 
 
-Device Naming
-=============
+.. _v4l2_device_naming:
+
+V4L2 Device Node 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
+The driver modules plug into the ``videodev`` kernel module. It provides
 helper functions and a common application interface specified in this
 document.
 
@@ -23,6 +25,42 @@ 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 V4L2 device node types 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. **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) provide a
+      different API and aren't considered as V4L2 device nodes.
+
+      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
-- 
2.13.5

[PATCH v6 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 7e7aad784388..18030131ef77 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -19,11 +19,10 @@ 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 V4L2 device node types are:
 
-- 
2.13.5

[PATCH v6 4/7] media: open.rst: document devnode-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 | 40 +++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 18030131ef77..bcfa654d5d71 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,6 +7,46 @@ Opening and Closing Devices
 ***************************
 
 
+.. _v4l2_hardware_control:
+
+
+Types of V4L2 hardware peripheral control
+=========================================
+
+V4L2 hardware periferal is usually complex: support for it is
+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`) with are responsible for implementing
+data streaming, if applicable.
+
+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
+of control as **V4L2 device node centric** (or, simply, "**vdev-centric**").
+
+Later (kernel 2.6.39), a new type of periferal control was
+added in order to support complex peripherals that are common for embedded
+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**") control.
+
+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 inform the application which device nodes are available
+(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.
+
 .. _v4l2_device_naming:
 
 V4L2 Device Node Naming
-- 
2.13.5

[PATCH v6 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 | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index bcfa654d5d71..e19295b6dafe 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -143,7 +143,7 @@ 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 V4L2 device nodes for each of these functions.
 
 The V4L2 API was designed with the idea that one device node could
 support all functions. However, in practice this never worked: this
@@ -153,17 +153,17 @@ 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.
 
 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 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
-- 
2.13.5

[PATCH v6 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>
---
 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 e19295b6dafe..7de8b2fe3096 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -47,6 +47,13 @@ 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.
 
+.. attention::
+
+   Devices that require **MC-centric** hardware peripheral 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 12e0d9a63cd8..3675f484b7ef 100644
--- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
+++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
@@ -252,6 +252,11 @@ 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 **vdev-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 45cf7359822c..a35d762c3eef 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 */
 
 /*
-- 
2.13.5

[PATCH v6 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>
---
 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 7de8b2fe3096..250f0b865943 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -47,6 +47,13 @@ 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.
 
+.. note::
+
+   A **vdev-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** hardware peripheral control should
-- 
2.13.5

Re: [PATCH v6 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec

[Hans Verkuil]

On 29/08/17 15:17, 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 | 150 ++++++++++++++++++++++++++++++
>  Documentation/media/uapi/v4l/v4l2.rst     |   1 +
>  2 files changed, 151 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..afafe1bc1894
> --- /dev/null
> +++ b/Documentation/media/uapi/v4l/glossary.rst
> @@ -0,0 +1,150 @@
> +========
> +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
> +	The same as V4L2 main driver.
> +
> +    Device Node
> +	A character device node in the file system used to control and do
> +	input/output data transfers from/to a Kernel driver.
> +
> +    Digital Signal Processor - DSP
> +	A specialized microprocessor, with its architecture optimized for
> +	the operational needs of digital signal processing.
> +
> +    Driver
> +	The part of the Linux Kernel that implements support
> +	for a hardware component.
> +
> +    Field-programmable Gate Array - FPGA
> +	A field-programmable gate array (FPGA) is an 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 media hardware. For example an I²C or SPI device,
> +	or an IP block inside an SoC or FPGA.
> +
> +    Hardware peripheral

As I mentioned before, I really don't like the term 'peripheral'. I am
fine with "Media hardware". A peripheral to me are keyboards, mice, webcams,
printers, etc. Not an SoC with a CSI sensor on the board.

> +	A group of hardware components that together make a larger
> +	user-facing functional peripheral. For instance the SoC ISP IP
> +	cores and external camera sensors together make a
> +	camera hardware peripheral.
> +
> +	Also known as peripheral.
> +
> +    Hardware peripheral control

So this would become "Media hardware control"

> +	Type of control for a hardware peripheral supported by V4L2 drivers.
> +
> +	See :ref:`v4l2_hardware_control`.
> +
> +    Inter-Integrated Circuit - I²C
> +	A  multi-master, multi-slave, packet switched, single-ended,
> +	serial computer bus used to control V4L2 sub-devices.
> +
> +	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> +
> +    Integrated circuit - IC
> +	A set of electronic circuits on one small flat piece of
> +	semiconductor material, normally silicon.
> +
> +	Also known as chip.
> +
> +    IP block
> +	The same as IP core.
> +
> +    Intelectual property core - IP core

Typo: Intellectual

> +	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).
> +
> +    Image Signal Processor - ISP
> +	A specialised processor 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).
> +
> +    Peripheral
> +	The same as hardware peripheral.

I'd drop this.

> +
> +    Media Controller
> +	An API designed to expose and control devices and sub-devices
> +	relationships to applications.
> +
> +	See :ref:`media_controller`.
> +
> +    MC-centric
> +	V4L2 hardware that requires a Media controller.
> +
> +	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 integrated circuit.
> +
> +    SMBus
> +	A subset of I²C, with defines a stricter usage of the bus.
> +
> +    Serial Peripheral Interface Bus - SPI
> +	Synchronous serial communication interface specification used for
> +	short distance communication, primarily in embedded systems.
> +
> +    System on a Chip - SoC
> +	An integrated circuit that integrates all components of a computer
> +	or other electronic systems.
> +
> +    Sub-device hardware components
> +	Hardware components that aren't controlled by the
> +	V4L2 main driver.

Do we really need this? If we do, then this description needs to be fixed:
you only say what it isn't controller by, not what actually does control it.

> +
> +    V4L2 device node
> +	A device node that is associated to a V4L2 main driver,
> +	as specified in :ref:`v4l2_device_naming`.
> +
> +    V4L2 hardware
> +	A hardware used to on a media device supported by the V4L2
> +	subsystem.
> +
> +    V4L2 hardware control
> +	The type of hardware control that a device supports.
> +
> +	See :ref:`v4l2_hardware_control`.

??? This is the same as "Hardware peripheral control". I'd stick to just one
term (i.e. "Media hardware control" as I proposed).

> +
> +    V4L2 main driver
> +	The V4L2 device driver that implements the main logic to talk with
> +	the V4L2 hardware.
> +
> +	Also known as bridge driver.
> +
> +	See :ref:`v4l2_hardware_control`.
> +
> +    V4L2 sub-device
> +	Part of the media hardware that it is implemented by a device

it is -> is

I don't think this is right. A V4L2 sub-device not hardware. It represents
a media hardware component and is implemented in a V4L2 sub-device driver.

> +	driver that is not part of the main V4L2 driver.
> +
> +	See :ref:`subdev`.
> +
> +    Vdev-centric

I strongly prefer to call this vdevnode-centric.
'vdev' is too vague and it only works for us because we use 'vdev' in our
code as the name for a video device node structure. End-users has no knowledge
of that.

I agree with the text in patches 2-7, except for the terminology.

If others agree, then once it is changed in a v7 patch series I'll review again
for consistent usage of the terminology.

Regards,

	Hans

> +	V4L2 hardware that it is controlled via V4L2 device nodes.
> +
> +	See :ref:`v4l2_hardware_control`.
> diff --git a/Documentation/media/uapi/v4l/v4l2.rst b/Documentation/media/uapi/v4l/v4l2.rst
> index f52a11c949d3..1ee4b86d18e1 100644
> --- a/Documentation/media/uapi/v4l/v4l2.rst
> +++ b/Documentation/media/uapi/v4l/v4l2.rst
> @@ -31,6 +31,7 @@ This part describes the Video for Linux API version 2 (V4L2 API) specification.
>      videodev
>      capture-example
>      v4l2grab-example
> +    glossary
>      biblio
>  
>  
> 

Re: [PATCH v6 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec

[Mauro Carvalho Chehab]

Em Fri, 1 Sep 2017 12:26:39 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On 29/08/17 15:17, 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 | 150 ++++++++++++++++++++++++++++++
> >  Documentation/media/uapi/v4l/v4l2.rst     |   1 +
> >  2 files changed, 151 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..afafe1bc1894
> > --- /dev/null
> > +++ b/Documentation/media/uapi/v4l/glossary.rst
> > @@ -0,0 +1,150 @@
> > +========
> > +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
> > +	The same as V4L2 main driver.
> > +
> > +    Device Node
> > +	A character device node in the file system used to control and do
> > +	input/output data transfers from/to a Kernel driver.
> > +
> > +    Digital Signal Processor - DSP
> > +	A specialized microprocessor, with its architecture optimized for
> > +	the operational needs of digital signal processing.
> > +
> > +    Driver
> > +	The part of the Linux Kernel that implements support
> > +	for a hardware component.
> > +
> > +    Field-programmable Gate Array - FPGA
> > +	A field-programmable gate array (FPGA) is an 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 media hardware. For example an I²C or SPI device,
> > +	or an IP block inside an SoC or FPGA.
> > +
> > +    Hardware peripheral  
> 
> As I mentioned before, I really don't like the term 'peripheral'. I am
> fine with "Media hardware". A peripheral to me are keyboards, mice, webcams,
> printers, etc. Not an SoC with a CSI sensor on the board.
> 
> > +	A group of hardware components that together make a larger
> > +	user-facing functional peripheral. For instance the SoC ISP IP
> > +	cores and external camera sensors together make a
> > +	camera hardware peripheral.
> > +
> > +	Also known as peripheral.
> > +
> > +    Hardware peripheral control  
> 
> So this would become "Media hardware control"
> 
> > +	Type of control for a hardware peripheral supported by V4L2 drivers.
> > +
> > +	See :ref:`v4l2_hardware_control`.
> > +
> > +    Inter-Integrated Circuit - I²C
> > +	A  multi-master, multi-slave, packet switched, single-ended,
> > +	serial computer bus used to control V4L2 sub-devices.
> > +
> > +	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> > +
> > +    Integrated circuit - IC
> > +	A set of electronic circuits on one small flat piece of
> > +	semiconductor material, normally silicon.
> > +
> > +	Also known as chip.
> > +
> > +    IP block
> > +	The same as IP core.
> > +
> > +    Intelectual property core - IP core  
> 
> Typo: Intellectual
> 
> > +	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).
> > +
> > +    Image Signal Processor - ISP
> > +	A specialised processor 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).
> > +
> > +    Peripheral
> > +	The same as hardware peripheral.  
> 
> I'd drop this.
> 
> > +
> > +    Media Controller
> > +	An API designed to expose and control devices and sub-devices
> > +	relationships to applications.
> > +
> > +	See :ref:`media_controller`.
> > +
> > +    MC-centric
> > +	V4L2 hardware that requires a Media controller.
> > +
> > +	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 integrated circuit.
> > +
> > +    SMBus
> > +	A subset of I²C, with defines a stricter usage of the bus.
> > +
> > +    Serial Peripheral Interface Bus - SPI
> > +	Synchronous serial communication interface specification used for
> > +	short distance communication, primarily in embedded systems.
> > +
> > +    System on a Chip - SoC
> > +	An integrated circuit that integrates all components of a computer
> > +	or other electronic systems.
> > +
> > +    Sub-device hardware components
> > +	Hardware components that aren't controlled by the
> > +	V4L2 main driver.  
> 
> Do we really need this? If we do, then this description needs to be fixed:
> you only say what it isn't controller by, not what actually does control it.
> 
> > +
> > +    V4L2 device node
> > +	A device node that is associated to a V4L2 main driver,
> > +	as specified in :ref:`v4l2_device_naming`.
> > +
> > +    V4L2 hardware
> > +	A hardware used to on a media device supported by the V4L2
> > +	subsystem.
> > +
> > +    V4L2 hardware control
> > +	The type of hardware control that a device supports.
> > +
> > +	See :ref:`v4l2_hardware_control`.  
> 
> ??? This is the same as "Hardware peripheral control". I'd stick to just one
> term (i.e. "Media hardware control" as I proposed).
> 
> > +
> > +    V4L2 main driver
> > +	The V4L2 device driver that implements the main logic to talk with
> > +	the V4L2 hardware.
> > +
> > +	Also known as bridge driver.
> > +
> > +	See :ref:`v4l2_hardware_control`.
> > +
> > +    V4L2 sub-device
> > +	Part of the media hardware that it is implemented by a device  
> 
> it is -> is
> 
> I don't think this is right. A V4L2 sub-device not hardware. It represents
> a media hardware component and is implemented in a V4L2 sub-device driver.
> 
> > +	driver that is not part of the main V4L2 driver.
> > +
> > +	See :ref:`subdev`.
> > +
> > +    Vdev-centric  
> 
> I strongly prefer to call this vdevnode-centric.
> 'vdev' is too vague and it only works for us because we use 'vdev' in our
> code as the name for a video device node structure. End-users has no knowledge
> of that.
> 
> I agree with the text in patches 2-7, except for the terminology.
> 
> If others agree, then once it is changed in a v7 patch series I'll review again
> for consistent usage of the terminology.

Addressed all above comments. The diff with regards to the previous
series is enclosed. I'll be sending the patches with those changes in
a few.

Regards,
Mauro


diff --git a/Documentation/media/uapi/v4l/glossary.rst b/Documentation/media/uapi/v4l/glossary.rst
index afafe1bc1894..b6767da1a46e 100644
--- a/Documentation/media/uapi/v4l/glossary.rst
+++ b/Documentation/media/uapi/v4l/glossary.rst
@@ -38,18 +38,12 @@ Glossary
 	A subset of the media hardware. For example an I²C or SPI device,
 	or an IP block inside an SoC or FPGA.
 
-    Hardware peripheral
-	A group of hardware components that together make a larger
-	user-facing functional peripheral. For instance the SoC ISP IP
-	cores and external camera sensors together make a
-	camera hardware peripheral.
-
-	Also known as peripheral.
-
-    Hardware peripheral control
-	Type of control for a hardware peripheral supported by V4L2 drivers.
-
-	See :ref:`v4l2_hardware_control`.
+    Image Signal Processor - ISP
+	A specialised processor 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).
 
     Inter-Integrated Circuit - I²C
 	A  multi-master, multi-slave, packet switched, single-ended,
@@ -63,10 +57,7 @@ Glossary
 
 	Also known as chip.
 
-    IP block
-	The same as IP core.
-
-    Intelectual property core - IP core
+    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.
@@ -75,15 +66,13 @@ Glossary
 
 	See https://en.wikipedia.org/wiki/Semiconductor_intellectual_property_core).
 
-    Image Signal Processor - ISP
-	A specialised processor 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).
+    IP block
+	The same as IP core.
 
-    Peripheral
-	The same as hardware peripheral.
+    MC-centric
+	V4L2 hardware that requires a Media controller.
+
+	See :ref:`v4l2_hardware_control`.
 
     Media Controller
 	An API designed to expose and control devices and sub-devices
@@ -91,8 +80,14 @@ Glossary
 
 	See :ref:`media_controller`.
 
-    MC-centric
-	V4L2 hardware that requires a Media controller.
+    Media hardware
+	A group of hardware components that together make a larger
+	user-facing functional media hardware. For instance the SoC ISP IP
+	cores and external camera sensors together make a
+	camera media hardware.
+
+    Media hardware control
+	Type of control for a media hardware supported by V4L2 drivers.
 
 	See :ref:`v4l2_hardware_control`.
 
@@ -113,10 +108,6 @@ Glossary
 	An integrated circuit that integrates all components of a computer
 	or other electronic systems.
 
-    Sub-device hardware components
-	Hardware components that aren't controlled by the
-	V4L2 main driver.
-
     V4L2 device node
 	A device node that is associated to a V4L2 main driver,
 	as specified in :ref:`v4l2_device_naming`.
@@ -125,11 +116,6 @@ Glossary
 	A hardware used to on a media device supported by the V4L2
 	subsystem.
 
-    V4L2 hardware control
-	The type of hardware control that a device supports.
-
-	See :ref:`v4l2_hardware_control`.
-
     V4L2 main driver
 	The V4L2 device driver that implements the main logic to talk with
 	the V4L2 hardware.
@@ -139,12 +125,12 @@ Glossary
 	See :ref:`v4l2_hardware_control`.
 
     V4L2 sub-device
-	Part of the media hardware that it is implemented by a device
-	driver that is not part of the main V4L2 driver.
+	Part of the media hardware that is implemented via a
+	V4L2 sub-device driver.
 
 	See :ref:`subdev`.
 
-    Vdev-centric
+    Vdevnode-centric
 	V4L2 hardware that it is controlled via V4L2 device nodes.
 
 	See :ref:`v4l2_hardware_control`.
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 250f0b865943..ed011ed123cc 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -10,8 +10,8 @@ Opening and Closing Devices
 .. _v4l2_hardware_control:
 
 
-Types of V4L2 hardware peripheral control
-=========================================
+Types of V4L2 media hardware control
+====================================
 
 V4L2 hardware periferal is usually complex: support for it is
 implemented via a V4L2 main driver and often by several additional drivers.
@@ -26,22 +26,22 @@ 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
-of control as **V4L2 device node centric** (or, simply, "**vdev-centric**").
+media hardware control: via the **V4L2 device nodes**. We refer to this kind
+of control as **V4L2 device node centric** (or, simply, "**vdevnode-centric**").
 
 Later (kernel 2.6.39), a new type of periferal control was
-added in order to support complex peripherals that are common for embedded
+added in order to support complex media hardware that are common for embedded
 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**") control.
 
-For **vdev-centric** hardware peripheral control, the peripheral is
+For **vdevnode-centric** media hardware control, the media hardware is
 controlled via the **V4L2 device nodes**. They may optionally support the
 :ref:`media controller API <media_controller>` as well,
 in order to inform the application which device nodes are available
 (see :ref:`related`).
 
-For **MC-centric** hardware peripheral control it is required to configure
+For **MC-centric** media hardware 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
@@ -49,14 +49,14 @@ device node per sub-device.
 
 .. note::
 
-   A **vdev-centric** may also optionally expose V4L2 sub-devices via
+   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** hardware peripheral control should
+   Devices that require **MC-centric** media hardware control should
    report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
    (see :ref:`VIDIOC_QUERYCAP`).
 
diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst
index cf69a5e33df2..944bc5ba484f 100644
--- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
+++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
@@ -257,7 +257,7 @@ specification the ioctl returns an ``EINVAL`` error code.
     * - ``V4L2_MC_CENTRIC``
       - 0x20000000
       - Indicates that the device require **MC-centric** hardware
-        control, and thus can't be used by **vdev-centric** applications.
+        control, and thus can't be used by **vdevnode-centric** applications.
         See :ref:`v4l2_hardware_control` for more details.
     * - ``V4L2_CAP_DEVICE_CAPS``
       - 0x80000000



Thanks,
Mauro

Re: [PATCH v6 2/7] media: open.rst: better document device node naming

[Sakari Ailus]

On Tue, Aug 29, 2017 at 10:17:51AM -0300, Mauro Carvalho Chehab wrote:
> 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.
> 
> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>

-- 
Sakari Ailus
e-mail: sakari.ailus@iki.fi