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.
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 | 147 +++++++++++++++++++++++
Documentation/media/uapi/v4l/open.rst | 114 +++++++++++++++---
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, 256 insertions(+), 14 deletions(-)
create mode 100644 Documentation/media/uapi/v4l/glossary.rst
--
2.13.5
As we now have a glossary, some terms used on open.rst
require adjustments.
Acked-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
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 21b8f7c5ca55..2575b6aea029 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -138,7 +138,7 @@ 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
@@ -148,17 +148,17 @@ 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
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 <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
Documentation/media/uapi/v4l/open.rst | 39 ++++++++++++++++++++++++++++++++---
1 file changed, 36 insertions(+), 3 deletions(-)
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index afd116edb40d..fc0037091814 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 +25,37 @@ 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 warranty 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/`` directoiries 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
+
+
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
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 <[email protected]>
---
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 2575b6aea029..275d934d2659 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
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 <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
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 fc0037091814..96ac972c1fa2 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
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 <[email protected]>
---
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 275d934d2659..ceffc87d7ca3 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
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 <[email protected]>
---
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 96ac972c1fa2..21b8f7c5ca55 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
Add a glossary of terms for V4L2, as several concepts are complex
enough to cause misunderstandings.
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
Documentation/media/uapi/v4l/glossary.rst | 147 ++++++++++++++++++++++++++++++
Documentation/media/uapi/v4l/v4l2.rst | 1 +
2 files changed, 148 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..0b6ab5adec81
--- /dev/null
+++ b/Documentation/media/uapi/v4l/glossary.rst
@@ -0,0 +1,147 @@
+========
+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 processor - ISP
+ A specialized digital signal processor used for image processing
+ in digital cameras, mobile phones or other devices.
+
+ Peripheral
+ The same as hardware peripheral.
+
+ Media Controller
+ An API used to identify the hardware components and (optionally)
+ change the links between hardware components.
+
+ 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
Hi Mauro,
Thanks for the update. A few comments below.
On Mon, Aug 28, 2017 at 09:53:55AM -0300, 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 <[email protected]>
> ---
> Documentation/media/uapi/v4l/glossary.rst | 147 ++++++++++++++++++++++++++++++
> Documentation/media/uapi/v4l/v4l2.rst | 1 +
> 2 files changed, 148 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..0b6ab5adec81
> --- /dev/null
> +++ b/Documentation/media/uapi/v4l/glossary.rst
> @@ -0,0 +1,147 @@
> +========
> +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.
I'd leave the WiP part out.
> +
> +.. Please keep the glossary entries in alphabetical order
> +
> +.. glossary::
> +
> + Bridge driver
> + The same as V4L2 main driver.
I've understood bridges being essentially a bus receiver + DMA. Most ISPs
contain both but have more than that. How about:
A driver for a bus (e.g. parallel, CSI-2) receiver and DMA. Bridge drivers
typically act as V4L2 main drivers.
> +
> + 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 I?C 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.
Aren't peripherals usually understood to be devices that you can plug into
a computer? Such as a printer, or a... floppy drive?
I certainly wouldn't call this a peripheral. How about "aggregate device"?
We haven't used that before, but I think it relatively well catches the
meaning without being excessively elaborate.
> +
> + Hardware peripheral control
> + Type of control for a hardware peripheral supported by V4L2 drivers.
> +
> + See :ref:`v4l2_hardware_control`.
> +
> + Inter-Integrated Circuit - I?C
> + 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 processor - ISP
"Image signal processor"
> + A specialized digital signal processor used for image processing
> + in digital cameras, mobile phones or other devices.
Traditional ISPs aren't programmable in the sense that you could execute
code in them. Instead, they implement a set of image processing algorithms
the parameters of which you can specify. How about:
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.
Peripheral generally is a very seldom used term nowadays, perhaps because
mostly you don't need to explicitly refer to external devices. I'd just
leave it out.
> +
> + Media Controller
> + An API used to identify the hardware components and (optionally)
> + change the links between hardware components.
IMO glossary is not where optional and mandatory parts of APIs should be
discussed. Just the scope. I.e. I'd leave "(optionally)" out. Change ->
configure.
The links are also between media entities, not hardware components. It is
not uncommon that a driver for a hardware component exposes several
sub-devices for the same component.
> +
> + 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 I?C, with defines a stricter usage of the bus.
> +
> + Serial Peripheral Interface Bus - SPI
We don't have "Bus" in I?C, I'd leave it out here, too.
> + 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`.
This will be confusing. Many sub-device nodes are exposed by so-called main
drivers.
I'd understand this as any device node type that is exposed by V4L2. In
general there should not be limitation on this, although video device nodes
are effectively only exposed by main drivers.
> +
> + 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.
Is UVC driver a bridge driver? How about instead:
Bridge and ISP drivers typically are V4L2 main drivers.
> +
> + 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.
How about:
V4L2 abstraction for a hardware component which is functionally or
physically separate from the DMA engine.
> +
> + 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
>
>
--
Kind regards,
Sakari Ailus
e-mail: [email protected]
Hi Mauro,
On Mon, Aug 28, 2017 at 09:53:56AM -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 <[email protected]>
> Signed-off-by: Mauro Carvalho Chehab <[email protected]>
> ---
> Documentation/media/uapi/v4l/open.rst | 39 ++++++++++++++++++++++++++++++++---
> 1 file changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> index afd116edb40d..fc0037091814 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 +25,37 @@ 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
Should we document V4L2 sub-device nodes here as well? They are implemented
by the V4L2 core as well as the other device node types.
Their purpose is somewhat different, though, and I think we'll need to make
that explicit somehow.
> +======================== ======================================================
> +
> +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 warranty that ``X`` will remain the same for the same
s/warranty/guarantee/
> + 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/`` directoiries containing
"directories"
> + 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
> +
> +
> 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
--
Kind regards,
Sakari Ailus
e-mail: [email protected]
On Mon, Aug 28, 2017 at 09:53:57AM -0300, Mauro Carvalho Chehab wrote:
> 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 <[email protected]>
> Signed-off-by: Mauro Carvalho Chehab <[email protected]>
Acked-by: Sakari Ailus <[email protected]>
--
Sakari Ailus
e-mail: [email protected]
Hi Sakari,
Em Tue, 29 Aug 2017 11:34:06 +0300
Sakari Ailus <[email protected]> escreveu:
> Hi Mauro,
>
> On Mon, Aug 28, 2017 at 09:53:56AM -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 <[email protected]>
> > Signed-off-by: Mauro Carvalho Chehab <[email protected]>
> > ---
> > Documentation/media/uapi/v4l/open.rst | 39 ++++++++++++++++++++++++++++++++---
> > 1 file changed, 36 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
> > index afd116edb40d..fc0037091814 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 +25,37 @@ 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
>
> Should we document V4L2 sub-device nodes here as well? They are implemented
> by the V4L2 core as well as the other device node types.
>
> Their purpose is somewhat different, though, and I think we'll need to make
> that explicit somehow.
Actually, what we're calling as "V4L2 Device node" are the vdev-centric
device nodes. That should not include /dev/v4l-subdevX.
What we can do here is to explicitly rule out the subdev interfaces,
with something like:
.. note::
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`.
>
> > +======================== ======================================================
> > +
> > +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 warranty that ``X`` will remain the same for the same
>
> s/warranty/guarantee/
OK.
>
> > + 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/`` directoiries containing
>
> "directories"
OK.
>
> > + 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
> > +
> > +
> > 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
>
Thanks,
Mauro
Em Tue, 29 Aug 2017 10:47:48 +0300
Sakari Ailus <[email protected]> escreveu:
> Hi Mauro,
>
> Thanks for the update. A few comments below.
>
> On Mon, Aug 28, 2017 at 09:53:55AM -0300, 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 <[email protected]>
> > ---
> > Documentation/media/uapi/v4l/glossary.rst | 147 ++++++++++++++++++++++++++++++
> > Documentation/media/uapi/v4l/v4l2.rst | 1 +
> > 2 files changed, 148 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..0b6ab5adec81
> > --- /dev/null
> > +++ b/Documentation/media/uapi/v4l/glossary.rst
> > @@ -0,0 +1,147 @@
> > +========
> > +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.
>
> I'd leave the WiP part out.
IMO, it is important to mention it, as the glossary, right now, covers
only what's used on the first two sections of the API book. There are
a lot more to be covered.
>
> > +
> > +.. Please keep the glossary entries in alphabetical order
> > +
> > +.. glossary::
> > +
> > + Bridge driver
> > + The same as V4L2 main driver.
>
> I've understood bridges being essentially a bus receiver + DMA. Most ISPs
> contain both but have more than that. How about:
>
> A driver for a bus (e.g. parallel, CSI-2) receiver and DMA. Bridge drivers
> typically act as V4L2 main drivers.
No, only on some drivers the bridge driver has DMA. A vast amount of
drivers (USB ones) don't implement any DMA inside the driver, as it is
up to the USB host driver to implement support for DMA.
There are even some USB host drivers that don't always use DMA for I/O
transfers, using direct I/O if the message is smaller than a threshold
or not multiple of the bus word. This is pretty common on SoC USB host
drivers.
In any case, for the effect of this spec, and for all discussions we
ever had about it, bridge driver == V4L2 main driver. I don't
see any reason why to distinguish between them.
>
> > +
> > + 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.
>
> Aren't peripherals usually understood to be devices that you can plug into
> a computer? Such as a printer, or a... floppy drive?
That is the common sense, although, technically, peripherals are any
I/O component. It is "peripheral" in the sense that it is not part of
the CPU's internal circuits. Instead, it is a data that should be sent
in or out the CPU.
On such concept, even an I/O hardware integrated inside a SoC is a
peripheral.
Yet, Hans argued already against using it. I opened a separate
thread for us to discuss about it.
> I certainly wouldn't call this a peripheral. How about "aggregate device"?
> We haven't used that before, but I think it relatively well catches the
> meaning without being excessively elaborate.
"aggregate device" means nothing to me ;-) I propose "media hardware" instead.
>
> > +
> > + 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 processor - ISP
>
> "Image signal processor"
OK.
>
> > + A specialized digital signal processor used for image processing
> > + in digital cameras, mobile phones or other devices.
>
> Traditional ISPs aren't programmable in the sense that you could execute
> code in them. Instead, they implement a set of image processing algorithms
> the parameters of which you can specify.
That definition came directly from Wikipedia :-)
> How about:
>
> 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).
Works for me.
>
> > +
> > + Peripheral
> > + The same as hardware peripheral.
>
> Peripheral generally is a very seldom used term nowadays, perhaps because
> mostly you don't need to explicitly refer to external devices. I'd just
> leave it out.
Let's discuss the usage of "peripheral" x "V4L2 hardware" x "media hardware".
Once we reach a consensus, I'll replace for whatever term we agree.
>
> > +
> > + Media Controller
> > + An API used to identify the hardware components and (optionally)
> > + change the links between hardware components.
>
> IMO glossary is not where optional and mandatory parts of APIs should be
> discussed. Just the scope. I.e. I'd leave "(optionally)" out. Change ->
> configure.
IMO, glossary should provide a summary of all terms used, specially
the ones that are defined at the API itself.
> The links are also between media entities, not hardware components. It is
> not uncommon that a driver for a hardware component exposes several
> sub-devices for the same component.
The concept of entities, links, interfaces, etc should be added at
the glossary, but IMHO it is out of the current scope: this glossary
is only at the V4L2 part of the spec, with doesn't cover MC.
I'm OK if you want to expand it to cover the entire uAPI book, but
I don't have any time for doing it myself.
So, I would prefer to keep the definition here as simple as possible.
What about:
An API designed to expose and control devices and sub-devices
relationships to applications.
(that's basically a quick summary of what's written at
media-controller-intro.rst)
>
> > +
> > + 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
>
> We don't have "Bus" in I²C, I'd leave it out here, too.
I2C is a serial bus (and it is implemented as a bus inside the Kernel).
Take a look at Documentation/i2c/summary.
> > + 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`.
>
> This will be confusing. Many sub-device nodes are exposed by so-called main
> drivers.
The sub-device nodes are not listed at v4l2_device_naming chapter. Also,
as I mentioned, I'm adding a notice there explicitly excluding them
from "V4L2 device node".
Btw, I don't know why (and where) a main driver would also be
exporting a sub-device. That seems to be a violation of the subdev API.
> I'd understand this as any device node type that is exposed by V4L2. In
> general there should not be limitation on this, although video device nodes
> are effectively only exposed by main drivers.
The goal of the glossary (and other changes in this series) is to
differentiate what is:
- V4L2 device node - e. g. /dev/video, /dev/radio, /dev/swradio,
/dev/vbi, /dev/v4l-touch (and only those)
- V4L2 sub-device node - e. g. /dev/v4l-subdev.
If you think this is not enough, we could repeat the above info, although,
IMHO, it is better to add refs to the right chapters, in order to avoid
the need of touching the glossary every time we add a new V4L2 device
node.
>
> > +
> > + 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.
>
> Is UVC driver a bridge driver? How about instead:
Yes, sure: UVC driver is a bridge driver/main driver. It is the UVC driver
that sends/receives data from the USB bus and send to the sensors.
It also sends data via URB to the USB host driver, with, in turn send it
to send to CPU (usually via DMA - although some USB drivers actually
implement direct I/O for short messages).
> Bridge and ISP drivers typically are V4L2 main drivers.
We don't have a concept of an "ISP driver". Adding it sounds very
confusing, as an ISP hardware may actually implement different
functions - so it ends by being supported by multiple drivers.
> > +
> > + 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.
>
> How about:
>
> V4L2 abstraction for a hardware component which is functionally or
> physically separate from the DMA engine.
That's actually not true. On vdev-centric devices, common ISP
controls (bright, color, saturation, etc) are actually implemented
by the main V4L2 driver.
Also, on USB drivers, the DMA engine is actually not implemented
by the main driver, but by the USB host 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
> >
> >
>
Thanks,
Mauro