[PATCH v9 0/5] Add a glossary for the media subsystem

[PATCH v9 0/5] Add a glossary for the media subsystem

[Mauro Carvalho Chehab]

There are too many technical terms at the media subsystem, and sometimes
the same thing is refered differently at the documentation and on the ML
and IRC discussions.

Let's add a glossary to the uAPI documentation, in order to start using
a common vocabulary at the subsystem's discussion and to let things
clearer for people trying to understand the subsystem.

I'm pretty sure that this document doesn't cover everything, but it can
(and should) be improved overtime.

At version 9 (and hopefully the final version), I simplified how things were
described, avoiding to define things that may not be needed for this
initial version, in order to try reach a consensus when merging.

If something is not ok, or other terms need to be added, feel free to
submit other patches addressing it.

Mauro Carvalho Chehab (5):
  media: open.rst: better document device node naming
  media: open.rst: remove the minor number range
  media: docs: add glossary.rst with common terms used at V4L2 spec
  media: glossary.rst: add terms for MC-centric video-node-centric
  media: open.rst: document mc-centric and video-node-centric

 .../userspace-api/media/glossary.rst          | 214 ++++++++++++++++++
 Documentation/userspace-api/media/index.rst   |   3 +
 .../userspace-api/media/v4l/open.rst          | 106 +++++++--
 3 files changed, 309 insertions(+), 14 deletions(-)
 create mode 100644 Documentation/userspace-api/media/glossary.rst

-- 
2.26.2

[PATCH v9 1/5] 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+huawei@kernel.org>
---
 .../userspace-api/media/v4l/open.rst          | 43 +++++++++++++++++--
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
index 38046ef20141..86816b247a17 100644
--- a/Documentation/userspace-api/media/v4l/open.rst
+++ b/Documentation/userspace-api/media/v4l/open.rst
@@ -14,12 +14,14 @@ 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.
 
@@ -30,6 +32,41 @@ 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 device nodes supported by the Video4Linux subsystem 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
+``/dev/v4l-sudevX``	 Video sub-devices (used by sensors and other I2C
+			 devices)\ [#]_
+======================== ======================================================
+
+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
+
+.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) use a different
+       set of system calls, as 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
-- 
2.26.2

[PATCH v9 2/5] 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+huawei@kernel.org>
---
 Documentation/userspace-api/media/v4l/open.rst | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
index 86816b247a17..ee4c8f123815 100644
--- a/Documentation/userspace-api/media/v4l/open.rst
+++ b/Documentation/userspace-api/media/v4l/open.rst
@@ -26,11 +26,10 @@ 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 device nodes supported by the Video4Linux subsystem are:
 
-- 
2.26.2

[PATCH v9 3/5] media: docs: add glossary.rst with common terms used at V4L2 spec

[Mauro Carvalho Chehab]

Add a glossary of terms used within the media userspace API
documentation, as several concepts are complex enough to cause
misunderstandings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
---
 .../userspace-api/media/glossary.rst          | 182 ++++++++++++++++++
 Documentation/userspace-api/media/index.rst   |   3 +
 2 files changed, 185 insertions(+)
 create mode 100644 Documentation/userspace-api/media/glossary.rst

diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
new file mode 100644
index 000000000000..18a1ace00159
--- /dev/null
+++ b/Documentation/userspace-api/media/glossary.rst
@@ -0,0 +1,182 @@
+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later
+
+.. For GPL-2.0, see LICENSES/preferred/GPL-2.0
+..
+.. For GFDL-1.1-or-later, see:
+..
+.. Permission is granted to copy, distribute and/or modify this document
+.. under the terms of the GNU Free Documentation License, Version 1.1 or
+.. any later version published by the Free Software Foundation, with no
+.. Invariant Sections, no Front-Cover Texts and no Back-Cover Texts.
+.. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+
+========
+Glossary
+========
+
+.. note::
+
+   This goal of this section is to standardize the terms used within the media
+   userspace API documentation. It is written incrementally as they are
+   standardized in the media documentation.
+
+   So, it is a Work In Progress.
+
+.. Please keep the glossary entries in alphabetical order
+
+.. glossary::
+
+    Bridge Driver
+	A :term:`device driver` that implements the main logic to talk with
+	media hardware.
+
+    CEC API
+	**Consumer Electronics Control API**
+
+	An API designed to receive and transmit data via an HDMI
+	CEC interface.
+
+	See :ref:`cec`.
+
+    Device Driver
+	Part of the Linux Kernel that implements support for a hardware
+	component.
+
+    Device Node
+	A character device node in the file system used to control and
+	ransfer data in and out of a Kernel driver.
+
+    Digital TV API
+	**Previously known as DVB API**
+
+	An API designed to control a subset of the :term:`Media Hardware`
+	that implements	digital TV.
+
+	See :ref:`dvbapi`.
+
+    DSP
+        **Digital Signal Processor**
+
+	A specialized :term:`Microprocessor`, with its architecture
+	optimized for the operational needs of digital signal processing.
+
+    FPGA
+	**Field-programmable Gate Array**
+
+	An :term:`IC` circuit designed to be configured by a customer or
+	a designer after manufacturing.
+
+	See https://en.wikipedia.org/wiki/Field-programmable_gate_array.
+
+    I²C
+	**Inter-Integrated Circuit**
+
+	A  multi-master, multi-slave, packet switched, single-ended,
+	serial computer bus used to control some hardware components
+	like sub-device hardware components.
+
+	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
+
+    IC
+	**Integrated circuit**
+
+	A set of electronic circuits on one small flat piece of
+	semiconductor material, normally silicon.
+
+	Also known as chip.
+
+    IP Block
+	**Intellectual property 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 Blocks 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).
+
+    ISP
+	**Image Signal Processor**
+
+	A specialized processor that implements a set of algorithms for
+	processing image data. ISPs may implement algorithms for lens
+	shading correction, demosaicing, 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).
+
+    Media API
+	A set of userspace APIs used to control the media hardware. It is
+	composed by:
+
+	  - :term:`CEC API`;
+	  - :term:`Digital TV API`;
+	  - :term:`MC API`;
+	  - :term:`RC API`; and
+	  - :term:`V4L2 API`.
+
+	See :doc:`v4l/v4l2`.
+
+    MC API
+	**Media Controller API**
+
+	An API designed to expose and control the relationships between
+	devices and sub-devices.
+
+	See :ref:`media_controller`.
+
+    Media Hardware
+	Subset of the hardware that is supported by the Linux Media API.
+
+	This includes audio and video capture and playback hardware,
+	digital and analog TV, camera sensors, ISPs, remote controllers,
+	codecs, HDMI Consumer Electronics Control, HDMI capture, etc.
+
+    Microprocessor
+	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.
+
+    RC API
+	**Remote Controller API**
+
+	An API designed to receive and transmit data from remote
+	controllers.
+
+	See :ref:`remote_controllers`.
+
+    SMBus
+	A subset of I²C, which defines a stricter usage of the bus.
+
+    SPI
+	**Serial Peripheral Interface Bus**
+
+	Synchronous serial communication interface specification used for
+	short distance communication, primarily in embedded systems.
+
+    SoC
+	**System on a Chip**
+
+	An integrated circuit that integrates all components of a computer
+	or other electronic systems.
+
+    V4L2 API
+	**V4L2 userspace API**
+
+	The userspace API defined in :ref:`v4l2spec`, which is used to
+	control a V4L2 hardware.
+
+    V4L2 Hardware
+	Part of a media hardware with is supported by the :term:`V4L2 API`.
+
+    V4L2 Sub-device
+	V4L2 hardware components that aren't controlled by a
+	:term:`bridge driver`.
+
+    V4L2 Sub-device API
+	Part of the :term:`V4L2 API` which control
+	:term:`V4L2 sub-devices <V4L2 Sub-device>`.
+
+	See :ref:`subdev`.
diff --git a/Documentation/userspace-api/media/index.rst b/Documentation/userspace-api/media/index.rst
index 70a3f3d73698..7f42f83b9f59 100644
--- a/Documentation/userspace-api/media/index.rst
+++ b/Documentation/userspace-api/media/index.rst
@@ -35,6 +35,9 @@ Please see:
     mediactl/media-controller
     cec/cec-api
     gen-errors
+
+    glossary
+
     fdl-appendix
 
     drivers/index
-- 
2.26.2

[PATCH v9 4/5] media: glossary.rst: add terms for MC-centric video-node-centric

[Mauro Carvalho Chehab]

Now that we have a chapter describing hardware control, let's
add the terms used there to the glossary.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
---
 .../userspace-api/media/glossary.rst          | 42 ++++++++++++++++---
 1 file changed, 37 insertions(+), 5 deletions(-)

diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
index 18a1ace00159..8cdb7900e994 100644
--- a/Documentation/userspace-api/media/glossary.rst
+++ b/Documentation/userspace-api/media/glossary.rst
@@ -69,6 +69,20 @@ Glossary
 
 	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 a
+	:term:`SoC` or :term:`FPGA`.
+
+    Hardware Peripheral
+	A group of :term:`hardware components <hardware component>` that
+	together make a larger user-facing functional peripheral. For
+	instance the :term:`SoC` :term:`ISP` :term:`IP	block <ip block>`
+	and external camera sensors together make a camera hardware
+	peripheral.
+
+	Also known as :term:`peripheral`.
+
     I²C
 	**Inter-Integrated Circuit**
 
@@ -126,6 +140,14 @@ Glossary
 
 	See :ref:`media_controller`.
 
+    MC-Centric
+	:term:`V4L2 hardware` that requires a :term:`MC API`.
+
+	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset
+	(see :ref:`VIDIOC_QUERYCAP`).
+
+	See :ref:`v4l2_hardware_control` for more details.
+
     Media Hardware
 	Subset of the hardware that is supported by the Linux Media API.
 
@@ -139,6 +161,9 @@ Glossary
 	control and input/output (I/O) operations specified by the
 	instructions on a single integrated circuit.
 
+    Peripheral
+	The same as :term:`hardware peripheral`.
+
     RC API
 	**Remote Controller API**
 
@@ -168,15 +193,22 @@ Glossary
 	The userspace API defined in :ref:`v4l2spec`, which is used to
 	control a V4L2 hardware.
 
+    V4L2 Device Node
+	A :term:`device node` that is associated to a V4L driver.
+
+	The V4L2 device node naming is specified at :ref:`v4l2_device_naming`.
+
     V4L2 Hardware
 	Part of a media hardware with is supported by the :term:`V4L2 API`.
 
     V4L2 Sub-device
 	V4L2 hardware components that aren't controlled by a
-	:term:`bridge driver`.
+	:term:`bridge driver`. See :ref:`subdev`.
 
-    V4L2 Sub-device API
-	Part of the :term:`V4L2 API` which control
-	:term:`V4L2 sub-devices <V4L2 Sub-device>`.
+    Video-node-Centric
+	V4L2 hardware that doesn't require a media controller to be used.
 
-	See :ref:`subdev`.
+	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset
+	(see :ref:`VIDIOC_QUERYCAP`).
+
+	See :ref:`v4l2_hardware_control` for more details.
-- 
2.26.2

[PATCH v9 5/5] media: open.rst: document mc-centric and video-node-centric

[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+huawei@kernel.org>
---
 .../userspace-api/media/v4l/open.rst          | 54 ++++++++++++++++---
 1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
index ee4c8f123815..8a9f766ab855 100644
--- a/Documentation/userspace-api/media/v4l/open.rst
+++ b/Documentation/userspace-api/media/v4l/open.rst
@@ -13,6 +13,48 @@
 Opening and Closing Devices
 ***************************
 
+.. _v4l2_hardware_control:
+
+Controlling a hardware peripheral via V4L2
+==========================================
+
+V4L2 hardware peripheral is usually complex: support for it is
+implemented via a bridge driver and often by several additional drivers.
+The bridge driver exposes one or more V4L2 device nodes
+(see :ref:`v4l2_device_naming`).
+
+There are other drivers providing support for other components of
+the hardware, with may also expose device nodes, called V4L2 sub-devices.
+
+When such V4L2 sub-devices are exposed, they allow controlling
+other hardware components - usually connected via a serial bus (like
+I²C, SMBus or SPI). Depending on the bridge driver, those sub-devices
+can be controlled indirectly via the bridge driver or explicitly via
+the :ref:`Media Controller <media_controller>` and via the
+:ref:`V4L2 sub-devices <subdev>`.
+
+The devices that require the use of the
+:ref:`Media Controller <media_controller>` are called **MC-centric**
+devices. The devices that are fully controlled via V4L2 device nodes
+are called **video-node-centric**.
+
+Userspace can check if a V4L2 hardware peripheral is MC-centric by
+calling :ref:`VIDIOC_QUERYCAP` and checking the
+:ref:`device_caps field <device-capabilities>`.
+
+If the device returns ``V4L2_CAP_IO_MC`` flag at ``device_caps``,
+it is MC-centric, otherwise, it is video-node-centric.
+
+It is required for MC-centric hardware to identify the V4L2
+sub-devices and to configure the pipelines via the
+:ref:`media controller API <media_controller>` before using the peripheral.
+Also, the sub-devices' configuration shall be controlled via the
+:ref:`sub-device API <subdev>`.
+
+.. note::
+
+   A video-node-centric may still provide a both media-controller and
+   sub-device interfaces as well.
 
 .. _v4l2_device_naming:
 
@@ -109,7 +151,7 @@ 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
@@ -119,17 +161,17 @@ 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
-- 
2.26.2

Re: [PATCH v9 1/5] media: open.rst: better document device node naming

[Hans Verkuil]

On 08/05/2020 15:10, 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.

identifier

> 
> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> ---
>  .../userspace-api/media/v4l/open.rst          | 43 +++++++++++++++++--
>  1 file changed, 40 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
> index 38046ef20141..86816b247a17 100644
> --- a/Documentation/userspace-api/media/v4l/open.rst
> +++ b/Documentation/userspace-api/media/v4l/open.rst
> @@ -14,12 +14,14 @@ 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.
>  
> @@ -30,6 +32,41 @@ 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 device nodes supported by the Video4Linux subsystem are:
> +
> +======================== ======================================================
> +Default device node name Usage
> +======================== ======================================================
> +``/dev/videoX``		 Video input/output devices

Also metadata input/output devices.

I would prefer capture/output given the traditional names that V4L2 uses.

> +``/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
> +``/dev/v4l-sudevX``	 Video sub-devices (used by sensors and other I2C

sudevX -> subdevX

You made this typo in more places, it's best to search and replace.

> +			 devices)\ [#]_

That suggests that subdevs are i2c devices, they can be any processing block on
any bus.

> +======================== ======================================================
> +
> +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
> +
> +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) use a different
> +       set of system calls, as 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

It looks like there is a missing period at the end of the sentence.

> 

Regards,

	Hans

Re: [PATCH v9 1/5] media: open.rst: better document device node naming

[Mauro Carvalho Chehab]

Em Fri, 8 May 2020 15:24:33 +0200
Hans Verkuil <hverkuil-cisco@xs4all.nl> escreveu:

> On 08/05/2020 15:10, 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.  
> 
> identifier
> 
> > 
> > Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > ---
> >  .../userspace-api/media/v4l/open.rst          | 43 +++++++++++++++++--
> >  1 file changed, 40 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
> > index 38046ef20141..86816b247a17 100644
> > --- a/Documentation/userspace-api/media/v4l/open.rst
> > +++ b/Documentation/userspace-api/media/v4l/open.rst
> > @@ -14,12 +14,14 @@ 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.
> >  
> > @@ -30,6 +32,41 @@ 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 device nodes supported by the Video4Linux subsystem are:
> > +
> > +======================== ======================================================
> > +Default device node name Usage
> > +======================== ======================================================
> > +``/dev/videoX``		 Video input/output devices  
> 
> Also metadata input/output devices.
> 
> I would prefer capture/output given the traditional names that V4L2 uses.
> 
> > +``/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
> > +``/dev/v4l-sudevX``	 Video sub-devices (used by sensors and other I2C  
> 
> sudevX -> subdevX
> 
> You made this typo in more places, it's best to search and replace.
> 
> > +			 devices)\ [#]_  
> 
> That suggests that subdevs are i2c devices, they can be any processing block on
> any bus.

For all the above: Ok. Will address at the next version.


> 
> > +======================== ======================================================
> > +
> > +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
> > +
> > +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) use a different
> > +       set of system calls, as 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  
> 
> It looks like there is a missing period at the end of the sentence.

The full sentence here is:

	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
	of leaving it to chance. When the driver supports multiple devices of
	the same type more than one device node number can be assigned,
	separated by commas:

This paragraph (untouched by this patch) sounds ok to me ;-)

Thanks,
Mauro

Re: [PATCH v9 3/5] media: docs: add glossary.rst with common terms used at V4L2 spec

[Hans Verkuil]

On 08/05/2020 15:10, Mauro Carvalho Chehab wrote:
> Add a glossary of terms used within the media userspace API
> documentation, as several concepts are complex enough to cause
> misunderstandings.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> ---
>  .../userspace-api/media/glossary.rst          | 182 ++++++++++++++++++
>  Documentation/userspace-api/media/index.rst   |   3 +
>  2 files changed, 185 insertions(+)
>  create mode 100644 Documentation/userspace-api/media/glossary.rst
> 
> diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
> new file mode 100644
> index 000000000000..18a1ace00159
> --- /dev/null
> +++ b/Documentation/userspace-api/media/glossary.rst
> @@ -0,0 +1,182 @@
> +.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later
> +
> +.. For GPL-2.0, see LICENSES/preferred/GPL-2.0
> +..
> +.. For GFDL-1.1-or-later, see:
> +..
> +.. Permission is granted to copy, distribute and/or modify this document
> +.. under the terms of the GNU Free Documentation License, Version 1.1 or
> +.. any later version published by the Free Software Foundation, with no
> +.. Invariant Sections, no Front-Cover Texts and no Back-Cover Texts.
> +.. A copy of the license is included at
> +.. Documentation/userspace-api/media/fdl-appendix.rst.
> +
> +========
> +Glossary
> +========
> +
> +.. note::
> +
> +   This goal of this section is to standardize the terms used within the media

This -> The

> +   userspace API documentation. It is written incrementally as they are
> +   standardized in the media documentation.
> +
> +   So, it is a Work In Progress.

I'd just say:

userspace API documentation. This is Work in Progress.

> +
> +.. Please keep the glossary entries in alphabetical order
> +
> +.. glossary::
> +
> +    Bridge Driver
> +	A :term:`device driver` that implements the main logic to talk with
> +	media hardware.
> +
> +    CEC API
> +	**Consumer Electronics Control API**
> +
> +	An API designed to receive and transmit data via an HDMI
> +	CEC interface.
> +
> +	See :ref:`cec`.
> +
> +    Device Driver
> +	Part of the Linux Kernel that implements support for a hardware
> +	component.
> +
> +    Device Node
> +	A character device node in the file system used to control and
> +	ransfer data in and out of a Kernel driver.

ransfer -> transfer

> +
> +    Digital TV API
> +	**Previously known as DVB API**
> +
> +	An API designed to control a subset of the :term:`Media Hardware`
> +	that implements	digital TV.

I think it will help to provide some examples, e.g.:

that implements digital TV (e.g. DVB, ATSC, etc.).

> +
> +	See :ref:`dvbapi`.
> +
> +    DSP
> +        **Digital Signal Processor**
> +
> +	A specialized :term:`Microprocessor`, with its architecture
> +	optimized for the operational needs of digital signal processing.
> +
> +    FPGA
> +	**Field-programmable Gate Array**
> +
> +	An :term:`IC` circuit designed to be configured by a customer or
> +	a designer after manufacturing.
> +
> +	See https://en.wikipedia.org/wiki/Field-programmable_gate_array.
> +
> +    I²C
> +	**Inter-Integrated Circuit**
> +
> +	A  multi-master, multi-slave, packet switched, single-ended,
> +	serial computer bus used to control some hardware components
> +	like sub-device hardware components.
> +
> +	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> +
> +    IC
> +	**Integrated circuit**
> +
> +	A set of electronic circuits on one small flat piece of
> +	semiconductor material, normally silicon.
> +
> +	Also known as chip.
> +
> +    IP Block
> +	**Intellectual property 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 Blocks 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).
> +
> +    ISP
> +	**Image Signal Processor**
> +
> +	A specialized processor that implements a set of algorithms for
> +	processing image data. ISPs may implement algorithms for lens
> +	shading correction, demosaicing, 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).
> +
> +    Media API
> +	A set of userspace APIs used to control the media hardware. It is
> +	composed by:
> +
> +	  - :term:`CEC API`;
> +	  - :term:`Digital TV API`;
> +	  - :term:`MC API`;
> +	  - :term:`RC API`; and
> +	  - :term:`V4L2 API`.
> +
> +	See :doc:`v4l/v4l2`.

Is that the right reference? I'd expect that v4l/v4l2 refers to the V4L2 API
and not the whole media API.

> +
> +    MC API
> +	**Media Controller API**
> +
> +	An API designed to expose and control the relationships between
> +	devices and sub-devices.

I'd say 'media devices and sub-devices'. Otherwise it would suggest that
the MC API also supports non-media devices.

> +
> +	See :ref:`media_controller`.
> +
> +    Media Hardware
> +	Subset of the hardware that is supported by the Linux Media API.
> +
> +	This includes audio and video capture and playback hardware,
> +	digital and analog TV, camera sensors, ISPs, remote controllers,
> +	codecs, HDMI Consumer Electronics Control, HDMI capture, etc.
> +
> +    Microprocessor
> +	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.
> +
> +    RC API
> +	**Remote Controller API**
> +
> +	An API designed to receive and transmit data from remote
> +	controllers.
> +
> +	See :ref:`remote_controllers`.
> +
> +    SMBus
> +	A subset of I²C, which defines a stricter usage of the bus.
> +
> +    SPI
> +	**Serial Peripheral Interface Bus**
> +
> +	Synchronous serial communication interface specification used for
> +	short distance communication, primarily in embedded systems.
> +
> +    SoC
> +	**System on a Chip**
> +
> +	An integrated circuit that integrates all components of a computer
> +	or other electronic systems.
> +
> +    V4L2 API
> +	**V4L2 userspace API**
> +
> +	The userspace API defined in :ref:`v4l2spec`, which is used to
> +	control a V4L2 hardware.
> +
> +    V4L2 Hardware
> +	Part of a media hardware with is supported by the :term:`V4L2 API`.

of a -> of the
with -> which

> +
> +    V4L2 Sub-device
> +	V4L2 hardware components that aren't controlled by a
> +	:term:`bridge driver`.

I'd give some examples here as well: sensors, HDMI receivers, scalers,
deinterlacers. Otherwise this is too vague.

> +
> +    V4L2 Sub-device API
> +	Part of the :term:`V4L2 API` which control

control -> controls

> +	:term:`V4L2 sub-devices <V4L2 Sub-device>`.
> +
> +	See :ref:`subdev`.
> diff --git a/Documentation/userspace-api/media/index.rst b/Documentation/userspace-api/media/index.rst
> index 70a3f3d73698..7f42f83b9f59 100644
> --- a/Documentation/userspace-api/media/index.rst
> +++ b/Documentation/userspace-api/media/index.rst
> @@ -35,6 +35,9 @@ Please see:
>      mediactl/media-controller
>      cec/cec-api
>      gen-errors
> +
> +    glossary
> +
>      fdl-appendix
>  
>      drivers/index
> 

Regards,

	Hans

Re: [PATCH v9 4/5] media: glossary.rst: add terms for MC-centric video-node-centric

[Hans Verkuil]

On 08/05/2020 15:10, Mauro Carvalho Chehab wrote:
> Now that we have a chapter describing hardware control, let's
> add the terms used there to the glossary.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> ---
>  .../userspace-api/media/glossary.rst          | 42 ++++++++++++++++---
>  1 file changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
> index 18a1ace00159..8cdb7900e994 100644
> --- a/Documentation/userspace-api/media/glossary.rst
> +++ b/Documentation/userspace-api/media/glossary.rst
> @@ -69,6 +69,20 @@ Glossary
>  
>  	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 a

inside a -> inside an

> +	:term:`SoC` or :term:`FPGA`.
> +
> +    Hardware Peripheral
> +	A group of :term:`hardware components <hardware component>` that
> +	together make a larger user-facing functional peripheral. For
> +	instance the :term:`SoC` :term:`ISP` :term:`IP	block <ip block>`

Are there some commas missing here after 'SoC' and 'ISP'?

> +	and external camera sensors together make a camera hardware
> +	peripheral.
> +
> +	Also known as :term:`peripheral`.
> +
>      I²C
>  	**Inter-Integrated Circuit**
>  
> @@ -126,6 +140,14 @@ Glossary
>  
>  	See :ref:`media_controller`.
>  
> +    MC-Centric
> +	:term:`V4L2 hardware` that requires a :term:`MC API`.

a -> the

> +
> +	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset

They have that capability set, not unset.

> +	(see :ref:`VIDIOC_QUERYCAP`).
> +
> +	See :ref:`v4l2_hardware_control` for more details.
> +
>      Media Hardware
>  	Subset of the hardware that is supported by the Linux Media API.
>  
> @@ -139,6 +161,9 @@ Glossary
>  	control and input/output (I/O) operations specified by the
>  	instructions on a single integrated circuit.
>  
> +    Peripheral
> +	The same as :term:`hardware peripheral`.
> +
>      RC API
>  	**Remote Controller API**
>  
> @@ -168,15 +193,22 @@ Glossary
>  	The userspace API defined in :ref:`v4l2spec`, which is used to
>  	control a V4L2 hardware.
>  
> +    V4L2 Device Node
> +	A :term:`device node` that is associated to a V4L driver.
> +
> +	The V4L2 device node naming is specified at :ref:`v4l2_device_naming`.
> +
>      V4L2 Hardware
>  	Part of a media hardware with is supported by the :term:`V4L2 API`.
>  
>      V4L2 Sub-device
>  	V4L2 hardware components that aren't controlled by a
> -	:term:`bridge driver`.
> +	:term:`bridge driver`. See :ref:`subdev`.
>  
> -    V4L2 Sub-device API
> -	Part of the :term:`V4L2 API` which control
> -	:term:`V4L2 sub-devices <V4L2 Sub-device>`.
> +    Video-node-Centric

Either Video-Node-Centric or Video-node-centric, but not Video-node-Centric,
that's inconsistent use of capitals.

> +	V4L2 hardware that doesn't require a media controller to be used.

a media controller to be used -> the MC API.

>  
> -	See :ref:`subdev`.
> +	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset
> +	(see :ref:`VIDIOC_QUERYCAP`).
> +
> +	See :ref:`v4l2_hardware_control` for more details.
> 

Regards,

	Hans

Re: [PATCH v9 5/5] media: open.rst: document mc-centric and video-node-centric

[Hans Verkuil]

On 08/05/2020 15:10, 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+huawei@kernel.org>
> ---
>  .../userspace-api/media/v4l/open.rst          | 54 ++++++++++++++++---
>  1 file changed, 48 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
> index ee4c8f123815..8a9f766ab855 100644
> --- a/Documentation/userspace-api/media/v4l/open.rst
> +++ b/Documentation/userspace-api/media/v4l/open.rst
> @@ -13,6 +13,48 @@
>  Opening and Closing Devices
>  ***************************
>  
> +.. _v4l2_hardware_control:
> +
> +Controlling a hardware peripheral via V4L2
> +==========================================
> +
> +V4L2 hardware peripheral is usually complex: support for it is

V4L2 -> A V4L2

> +implemented via a bridge driver and often by several additional drivers.
> +The bridge driver exposes one or more V4L2 device nodes
> +(see :ref:`v4l2_device_naming`).
> +
> +There are other drivers providing support for other components of
> +the hardware, with may also expose device nodes, called V4L2 sub-devices.

with -> which

> +
> +When such V4L2 sub-devices are exposed, they allow controlling
> +other hardware components - usually connected via a serial bus (like

other -> those other

> +I²C, SMBus or SPI). Depending on the bridge driver, those sub-devices
> +can be controlled indirectly via the bridge driver or explicitly via
> +the :ref:`Media Controller <media_controller>` and via the
> +:ref:`V4L2 sub-devices <subdev>`.
> +
> +The devices that require the use of the
> +:ref:`Media Controller <media_controller>` are called **MC-centric**
> +devices. The devices that are fully controlled via V4L2 device nodes
> +are called **video-node-centric**.
> +
> +Userspace can check if a V4L2 hardware peripheral is MC-centric by
> +calling :ref:`VIDIOC_QUERYCAP` and checking the
> +:ref:`device_caps field <device-capabilities>`.
> +
> +If the device returns ``V4L2_CAP_IO_MC`` flag at ``device_caps``,
> +it is MC-centric, otherwise, it is video-node-centric.

then it is MC-centric, otherwise it is video-node-centric.

> +
> +It is required for MC-centric hardware to identify the V4L2
> +sub-devices and to configure the pipelines via the
> +:ref:`media controller API <media_controller>` before using the peripheral.
> +Also, the sub-devices' configuration shall be controlled via the
> +:ref:`sub-device API <subdev>`.
> +
> +.. note::
> +
> +   A video-node-centric may still provide a both media-controller and

a both -> the

> +   sub-device interfaces as well.

Add:

However, in that case the media-controller and the sub-device interfaces
are read-only and just provide information about the device. The actual
configuration is done via the video nodes.

>  
>  .. _v4l2_device_naming:
>  
> @@ -109,7 +151,7 @@ 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
> @@ -119,17 +161,17 @@ 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
> 

Regards,

	Hans

Re: [PATCH v9 1/5] media: open.rst: better document device node naming

[Hans Verkuil]

On 08/05/2020 15:35, Mauro Carvalho Chehab wrote:
> Em Fri, 8 May 2020 15:24:33 +0200
> Hans Verkuil <hverkuil-cisco@xs4all.nl> escreveu:
> 
>> On 08/05/2020 15:10, 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.  
>>
>> identifier
>>
>>>
>>> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
>>> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
>>> ---
>>>  .../userspace-api/media/v4l/open.rst          | 43 +++++++++++++++++--
>>>  1 file changed, 40 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
>>> index 38046ef20141..86816b247a17 100644
>>> --- a/Documentation/userspace-api/media/v4l/open.rst
>>> +++ b/Documentation/userspace-api/media/v4l/open.rst
>>> @@ -14,12 +14,14 @@ 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.
>>>  
>>> @@ -30,6 +32,41 @@ 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 device nodes supported by the Video4Linux subsystem are:
>>> +
>>> +======================== ======================================================
>>> +Default device node name Usage
>>> +======================== ======================================================
>>> +``/dev/videoX``		 Video input/output devices  
>>
>> Also metadata input/output devices.
>>
>> I would prefer capture/output given the traditional names that V4L2 uses.
>>
>>> +``/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
>>> +``/dev/v4l-sudevX``	 Video sub-devices (used by sensors and other I2C  
>>
>> sudevX -> subdevX
>>
>> You made this typo in more places, it's best to search and replace.
>>
>>> +			 devices)\ [#]_  
>>
>> That suggests that subdevs are i2c devices, they can be any processing block on
>> any bus.
> 
> For all the above: Ok. Will address at the next version.
> 
> 
>>
>>> +======================== ======================================================
>>> +
>>> +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
>>> +
>>> +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-sudevX``) use a different
>>> +       set of system calls, as 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  
>>
>> It looks like there is a missing period at the end of the sentence.
> 
> The full sentence here is:
> 
> 	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
> 	of leaving it to chance. When the driver supports multiple devices of
> 	the same type more than one device node number can be assigned,
> 	separated by commas:
> 
> This paragraph (untouched by this patch) sounds ok to me ;-)

Ah yes, I misread the patch. It looked like there was an empty line after
'instead'. Never mind :-)

Regards,

	Hans

> 
> Thanks,
> Mauro
> 

Re: [PATCH v9 3/5] media: docs: add glossary.rst with common terms used at V4L2 spec

[Mauro Carvalho Chehab]

Em Fri, 8 May 2020 15:40:25 +0200
Hans Verkuil <hverkuil-cisco@xs4all.nl> escreveu:

> On 08/05/2020 15:10, Mauro Carvalho Chehab wrote:
> > Add a glossary of terms used within the media userspace API
> > documentation, as several concepts are complex enough to cause
> > misunderstandings.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > ---
> >  .../userspace-api/media/glossary.rst          | 182 ++++++++++++++++++
> >  Documentation/userspace-api/media/index.rst   |   3 +
> >  2 files changed, 185 insertions(+)
> >  create mode 100644 Documentation/userspace-api/media/glossary.rst
> > 
> > diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
> > new file mode 100644
> > index 000000000000..18a1ace00159
> > --- /dev/null
> > +++ b/Documentation/userspace-api/media/glossary.rst
> > @@ -0,0 +1,182 @@
> > +.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later
> > +
> > +.. For GPL-2.0, see LICENSES/preferred/GPL-2.0
> > +..
> > +.. For GFDL-1.1-or-later, see:
> > +..
> > +.. Permission is granted to copy, distribute and/or modify this document
> > +.. under the terms of the GNU Free Documentation License, Version 1.1 or
> > +.. any later version published by the Free Software Foundation, with no
> > +.. Invariant Sections, no Front-Cover Texts and no Back-Cover Texts.
> > +.. A copy of the license is included at
> > +.. Documentation/userspace-api/media/fdl-appendix.rst.
> > +
> > +========
> > +Glossary
> > +========
> > +
> > +.. note::
> > +
> > +   This goal of this section is to standardize the terms used within the media  
> 
> This -> The
> 
> > +   userspace API documentation. It is written incrementally as they are
> > +   standardized in the media documentation.
> > +
> > +   So, it is a Work In Progress.  
> 
> I'd just say:
> 
> userspace API documentation. This is Work in Progress.
> 
> > +
> > +.. Please keep the glossary entries in alphabetical order
> > +
> > +.. glossary::
> > +
> > +    Bridge Driver
> > +	A :term:`device driver` that implements the main logic to talk with
> > +	media hardware.
> > +
> > +    CEC API
> > +	**Consumer Electronics Control API**
> > +
> > +	An API designed to receive and transmit data via an HDMI
> > +	CEC interface.
> > +
> > +	See :ref:`cec`.
> > +
> > +    Device Driver
> > +	Part of the Linux Kernel that implements support for a hardware
> > +	component.
> > +
> > +    Device Node
> > +	A character device node in the file system used to control and
> > +	ransfer data in and out of a Kernel driver.  
> 
> ransfer -> transfer
> 
> > +
> > +    Digital TV API
> > +	**Previously known as DVB API**
> > +
> > +	An API designed to control a subset of the :term:`Media Hardware`
> > +	that implements	digital TV.  
> 
> I think it will help to provide some examples, e.g.:
> 
> that implements digital TV (e.g. DVB, ATSC, etc.).

For the above: Ok!

> 
> > +
> > +	See :ref:`dvbapi`.
> > +
> > +    DSP
> > +        **Digital Signal Processor**
> > +
> > +	A specialized :term:`Microprocessor`, with its architecture
> > +	optimized for the operational needs of digital signal processing.
> > +
> > +    FPGA
> > +	**Field-programmable Gate Array**
> > +
> > +	An :term:`IC` circuit designed to be configured by a customer or
> > +	a designer after manufacturing.
> > +
> > +	See https://en.wikipedia.org/wiki/Field-programmable_gate_array.
> > +
> > +    I²C
> > +	**Inter-Integrated Circuit**
> > +
> > +	A  multi-master, multi-slave, packet switched, single-ended,
> > +	serial computer bus used to control some hardware components
> > +	like sub-device hardware components.
> > +
> > +	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> > +
> > +    IC
> > +	**Integrated circuit**
> > +
> > +	A set of electronic circuits on one small flat piece of
> > +	semiconductor material, normally silicon.
> > +
> > +	Also known as chip.
> > +
> > +    IP Block
> > +	**Intellectual property 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 Blocks 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).
> > +
> > +    ISP
> > +	**Image Signal Processor**
> > +
> > +	A specialized processor that implements a set of algorithms for
> > +	processing image data. ISPs may implement algorithms for lens
> > +	shading correction, demosaicing, 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).
> > +
> > +    Media API
> > +	A set of userspace APIs used to control the media hardware. It is
> > +	composed by:
> > +
> > +	  - :term:`CEC API`;
> > +	  - :term:`Digital TV API`;
> > +	  - :term:`MC API`;
> > +	  - :term:`RC API`; and
> > +	  - :term:`V4L2 API`.
> > +
> > +	See :doc:`v4l/v4l2`.  
> 
> Is that the right reference? I'd expect that v4l/v4l2 refers to the V4L2 API
> and not the whole media API.

That's the right reference: userspace-api/media/v4l/v4l2.rst file has
just the V4L2 API.

The entire API file is now at userspace-api/media/index.html.

> 
> > +
> > +    MC API
> > +	**Media Controller API**
> > +
> > +	An API designed to expose and control the relationships between
> > +	devices and sub-devices.  
> 
> I'd say 'media devices and sub-devices'. Otherwise it would suggest that
> the MC API also supports non-media devices.

Yeah, it sounds too generic, but MC is currently used also by audio
devices.

Ok, "audio" is "media", but not covered by this spec. 

We might use "multimedia" or some similar word. What do you think?

Thanks,
Mauro

Re: [PATCH v9 4/5] media: glossary.rst: add terms for MC-centric video-node-centric

[Mauro Carvalho Chehab]

Em Fri, 8 May 2020 15:46:50 +0200
Hans Verkuil <hverkuil-cisco@xs4all.nl> escreveu:

> On 08/05/2020 15:10, Mauro Carvalho Chehab wrote:
> > Now that we have a chapter describing hardware control, let's
> > add the terms used there to the glossary.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > ---
> >  .../userspace-api/media/glossary.rst          | 42 ++++++++++++++++---
> >  1 file changed, 37 insertions(+), 5 deletions(-)
> > 
> > diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
> > index 18a1ace00159..8cdb7900e994 100644
> > --- a/Documentation/userspace-api/media/glossary.rst
> > +++ b/Documentation/userspace-api/media/glossary.rst
> > @@ -69,6 +69,20 @@ Glossary
> >  
> >  	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 a  
> 
> inside a -> inside an
> 
> > +	:term:`SoC` or :term:`FPGA`.
> > +
> > +    Hardware Peripheral
> > +	A group of :term:`hardware components <hardware component>` that
> > +	together make a larger user-facing functional peripheral. For
> > +	instance the :term:`SoC` :term:`ISP` :term:`IP	block <ip block>`  
> 
> Are there some commas missing here after 'SoC' and 'ISP'?

There is a comma missing, but not at the place you pointed (IMHO) ;-)

Removing the :term: markup, what the above is saying is:

	For  instance, the SoC ISP IP block and external camera 
	sensors together make a camera hardware peripheral.

Ok, we could just call it as "ISP", instead of trying to be too
formal.

> 
> > +	and external camera sensors together make a camera hardware
> > +	peripheral.
> > +
> > +	Also known as :term:`peripheral`.
> > +
> >      I²C
> >  	**Inter-Integrated Circuit**
> >  
> > @@ -126,6 +140,14 @@ Glossary
> >  
> >  	See :ref:`media_controller`.
> >  
> > +    MC-Centric
> > +	:term:`V4L2 hardware` that requires a :term:`MC API`.  
> 
> a -> the
> 
> > +
> > +	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset  
> 
> They have that capability set, not unset.

Sorry, cut and paste error... it is identical to the video-node-centric
below ;-)

> 
> > +	(see :ref:`VIDIOC_QUERYCAP`).
> > +
> > +	See :ref:`v4l2_hardware_control` for more details.
> > +
> >      Media Hardware
> >  	Subset of the hardware that is supported by the Linux Media API.
> >  
> > @@ -139,6 +161,9 @@ Glossary
> >  	control and input/output (I/O) operations specified by the
> >  	instructions on a single integrated circuit.
> >  
> > +    Peripheral
> > +	The same as :term:`hardware peripheral`.
> > +
> >      RC API
> >  	**Remote Controller API**
> >  
> > @@ -168,15 +193,22 @@ Glossary
> >  	The userspace API defined in :ref:`v4l2spec`, which is used to
> >  	control a V4L2 hardware.
> >  
> > +    V4L2 Device Node
> > +	A :term:`device node` that is associated to a V4L driver.
> > +
> > +	The V4L2 device node naming is specified at :ref:`v4l2_device_naming`.
> > +
> >      V4L2 Hardware
> >  	Part of a media hardware with is supported by the :term:`V4L2 API`.
> >  
> >      V4L2 Sub-device
> >  	V4L2 hardware components that aren't controlled by a
> > -	:term:`bridge driver`.
> > +	:term:`bridge driver`. See :ref:`subdev`.
> >  
> > -    V4L2 Sub-device API
> > -	Part of the :term:`V4L2 API` which control
> > -	:term:`V4L2 sub-devices <V4L2 Sub-device>`.
> > +    Video-node-Centric  
> 
> Either Video-Node-Centric or Video-node-centric, but not Video-node-Centric,
> that's inconsistent use of capitals.

Ok.

> 
> > +	V4L2 hardware that doesn't require a media controller to be used.  
> 
> a media controller to be used -> the MC API.
> 
> >  
> > -	See :ref:`subdev`.
> > +	Such hardware have ``V4L2_CAP_IO_MC`` device_caps field unset
> > +	(see :ref:`VIDIOC_QUERYCAP`).
> > +
> > +	See :ref:`v4l2_hardware_control` for more details.
> >   
> 
> Regards,
> 
> 	Hans



Thanks,
Mauro

Re: [PATCH v9 3/5] media: docs: add glossary.rst with common terms used at V4L2 spec

[Hans Verkuil]

On 08/05/2020 16:25, Mauro Carvalho Chehab wrote:
> Em Fri, 8 May 2020 15:40:25 +0200
> Hans Verkuil <hverkuil-cisco@xs4all.nl> escreveu:
> 
>> On 08/05/2020 15:10, Mauro Carvalho Chehab wrote:
>>> Add a glossary of terms used within the media userspace API
>>> documentation, as several concepts are complex enough to cause
>>> misunderstandings.
>>>
>>> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
>>> ---
>>>  .../userspace-api/media/glossary.rst          | 182 ++++++++++++++++++
>>>  Documentation/userspace-api/media/index.rst   |   3 +
>>>  2 files changed, 185 insertions(+)
>>>  create mode 100644 Documentation/userspace-api/media/glossary.rst
>>>
>>> diff --git a/Documentation/userspace-api/media/glossary.rst b/Documentation/userspace-api/media/glossary.rst
>>> new file mode 100644
>>> index 000000000000..18a1ace00159
>>> --- /dev/null
>>> +++ b/Documentation/userspace-api/media/glossary.rst
>>> @@ -0,0 +1,182 @@
>>> +.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-or-later
>>> +
>>> +.. For GPL-2.0, see LICENSES/preferred/GPL-2.0
>>> +..
>>> +.. For GFDL-1.1-or-later, see:
>>> +..
>>> +.. Permission is granted to copy, distribute and/or modify this document
>>> +.. under the terms of the GNU Free Documentation License, Version 1.1 or
>>> +.. any later version published by the Free Software Foundation, with no
>>> +.. Invariant Sections, no Front-Cover Texts and no Back-Cover Texts.
>>> +.. A copy of the license is included at
>>> +.. Documentation/userspace-api/media/fdl-appendix.rst.
>>> +
>>> +========
>>> +Glossary
>>> +========
>>> +
>>> +.. note::
>>> +
>>> +   This goal of this section is to standardize the terms used within the media  
>>
>> This -> The
>>
>>> +   userspace API documentation. It is written incrementally as they are
>>> +   standardized in the media documentation.
>>> +
>>> +   So, it is a Work In Progress.  
>>
>> I'd just say:
>>
>> userspace API documentation. This is Work in Progress.
>>
>>> +
>>> +.. Please keep the glossary entries in alphabetical order
>>> +
>>> +.. glossary::
>>> +
>>> +    Bridge Driver
>>> +	A :term:`device driver` that implements the main logic to talk with
>>> +	media hardware.
>>> +
>>> +    CEC API
>>> +	**Consumer Electronics Control API**
>>> +
>>> +	An API designed to receive and transmit data via an HDMI
>>> +	CEC interface.
>>> +
>>> +	See :ref:`cec`.
>>> +
>>> +    Device Driver
>>> +	Part of the Linux Kernel that implements support for a hardware
>>> +	component.
>>> +
>>> +    Device Node
>>> +	A character device node in the file system used to control and
>>> +	ransfer data in and out of a Kernel driver.  
>>
>> ransfer -> transfer
>>
>>> +
>>> +    Digital TV API
>>> +	**Previously known as DVB API**
>>> +
>>> +	An API designed to control a subset of the :term:`Media Hardware`
>>> +	that implements	digital TV.  
>>
>> I think it will help to provide some examples, e.g.:
>>
>> that implements digital TV (e.g. DVB, ATSC, etc.).
> 
> For the above: Ok!
> 
>>
>>> +
>>> +	See :ref:`dvbapi`.
>>> +
>>> +    DSP
>>> +        **Digital Signal Processor**
>>> +
>>> +	A specialized :term:`Microprocessor`, with its architecture
>>> +	optimized for the operational needs of digital signal processing.
>>> +
>>> +    FPGA
>>> +	**Field-programmable Gate Array**
>>> +
>>> +	An :term:`IC` circuit designed to be configured by a customer or
>>> +	a designer after manufacturing.
>>> +
>>> +	See https://en.wikipedia.org/wiki/Field-programmable_gate_array.
>>> +
>>> +    I²C
>>> +	**Inter-Integrated Circuit**
>>> +
>>> +	A  multi-master, multi-slave, packet switched, single-ended,
>>> +	serial computer bus used to control some hardware components
>>> +	like sub-device hardware components.
>>> +
>>> +	See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
>>> +
>>> +    IC
>>> +	**Integrated circuit**
>>> +
>>> +	A set of electronic circuits on one small flat piece of
>>> +	semiconductor material, normally silicon.
>>> +
>>> +	Also known as chip.
>>> +
>>> +    IP Block
>>> +	**Intellectual property 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 Blocks 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).
>>> +
>>> +    ISP
>>> +	**Image Signal Processor**
>>> +
>>> +	A specialized processor that implements a set of algorithms for
>>> +	processing image data. ISPs may implement algorithms for lens
>>> +	shading correction, demosaicing, 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).
>>> +
>>> +    Media API
>>> +	A set of userspace APIs used to control the media hardware. It is
>>> +	composed by:
>>> +
>>> +	  - :term:`CEC API`;
>>> +	  - :term:`Digital TV API`;
>>> +	  - :term:`MC API`;
>>> +	  - :term:`RC API`; and
>>> +	  - :term:`V4L2 API`.
>>> +
>>> +	See :doc:`v4l/v4l2`.  
>>
>> Is that the right reference? I'd expect that v4l/v4l2 refers to the V4L2 API
>> and not the whole media API.
> 
> That's the right reference: userspace-api/media/v4l/v4l2.rst file has
> just the V4L2 API.

That's what I mean: This is the glossary entry for 'Media API', so why have a reference
to the V4L2 API? I expect to see a reference to the top-level media API.

> 
> The entire API file is now at userspace-api/media/index.html.
> 
>>
>>> +
>>> +    MC API
>>> +	**Media Controller API**
>>> +
>>> +	An API designed to expose and control the relationships between
>>> +	devices and sub-devices.  
>>
>> I'd say 'media devices and sub-devices'. Otherwise it would suggest that
>> the MC API also supports non-media devices.
> 
> Yeah, it sounds too generic, but MC is currently used also by audio
> devices.>
> Ok, "audio" is "media", but not covered by this spec. 
> 
> We might use "multimedia" or some similar word. What do you think?

Multimedia is fine. Or audio/video.

Regards,

	Hans

> 
> Thanks,
> Mauro
>