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SubjectRe: [PATCH v6 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec
Em Fri, 1 Sep 2017 12:26:39 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On 29/08/17 15:17, Mauro Carvalho Chehab wrote:
> > Add a glossary of terms for V4L2, as several concepts are complex
> > enough to cause misunderstandings.
> >
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> > ---
> > Documentation/media/uapi/v4l/glossary.rst | 150 ++++++++++++++++++++++++++++++
> > Documentation/media/uapi/v4l/v4l2.rst | 1 +
> > 2 files changed, 151 insertions(+)
> > create mode 100644 Documentation/media/uapi/v4l/glossary.rst
> >
> > diff --git a/Documentation/media/uapi/v4l/glossary.rst b/Documentation/media/uapi/v4l/glossary.rst
> > new file mode 100644
> > index 000000000000..afafe1bc1894
> > --- /dev/null
> > +++ b/Documentation/media/uapi/v4l/glossary.rst
> > @@ -0,0 +1,150 @@
> > +========
> > +Glossary
> > +========
> > +
> > +.. note::
> > +
> > + This goal of section is to standardize the terms used within the V4L2
> > + documentation. It is written incrementally as they are standardized in
> > + the V4L2 documentation. So, it is a Work In Progress.
> > +
> > +.. Please keep the glossary entries in alphabetical order
> > +
> > +.. glossary::
> > +
> > + Bridge driver
> > + The same as V4L2 main driver.
> > +
> > + Device Node
> > + A character device node in the file system used to control and do
> > + input/output data transfers from/to a Kernel driver.
> > +
> > + Digital Signal Processor - DSP
> > + A specialized microprocessor, with its architecture optimized for
> > + the operational needs of digital signal processing.
> > +
> > + Driver
> > + The part of the Linux Kernel that implements support
> > + for a hardware component.
> > +
> > + Field-programmable Gate Array - FPGA
> > + A field-programmable gate array (FPGA) is an integrated circuit
> > + designed to be configured by a customer or a designer after
> > + manufacturing.
> > +
> > + See https://en.wikipedia.org/wiki/Field-programmable_gate_array.
> > +
> > + Hardware component
> > + A subset of the media hardware. For example an I²C or SPI device,
> > + or an IP block inside an SoC or FPGA.
> > +
> > + Hardware peripheral
>
> As I mentioned before, I really don't like the term 'peripheral'. I am
> fine with "Media hardware". A peripheral to me are keyboards, mice, webcams,
> printers, etc. Not an SoC with a CSI sensor on the board.
>
> > + A group of hardware components that together make a larger
> > + user-facing functional peripheral. For instance the SoC ISP IP
> > + cores and external camera sensors together make a
> > + camera hardware peripheral.
> > +
> > + Also known as peripheral.
> > +
> > + Hardware peripheral control
>
> So this would become "Media hardware control"
>
> > + Type of control for a hardware peripheral supported by V4L2 drivers.
> > +
> > + See :ref:`v4l2_hardware_control`.
> > +
> > + Inter-Integrated Circuit - I²C
> > + A multi-master, multi-slave, packet switched, single-ended,
> > + serial computer bus used to control V4L2 sub-devices.
> > +
> > + See http://www.nxp.com/docs/en/user-guide/UM10204.pdf.
> > +
> > + Integrated circuit - IC
> > + A set of electronic circuits on one small flat piece of
> > + semiconductor material, normally silicon.
> > +
> > + Also known as chip.
> > +
> > + IP block
> > + The same as IP core.
> > +
> > + Intelectual property core - IP core
>
> Typo: Intellectual
>
> > + In electronic design a semiconductor intellectual property core,
> > + is a reusable unit of logic, cell, or integrated circuit layout
> > + design that is the intellectual property of one party.
> > + IP cores may be licensed to another party or can be owned
> > + and used by a single party alone.
> > +
> > + See https://en.wikipedia.org/wiki/Semiconductor_intellectual_property_core).
> > +
> > + Image Signal Processor - ISP
> > + A specialised processor that implements a set of algorithms for
> > + processing image data. ISPs may implement algorithms for lens
> > + shading correction, demosaic, scaling and pixel format conversion
> > + as well as produce statistics for the use of the control
> > + algorithms (e.g. automatic exposure, white balance and focus).
> > +
> > + Peripheral
> > + The same as hardware peripheral.
>
> I'd drop this.
>
> > +
> > + Media Controller
> > + An API designed to expose and control devices and sub-devices
> > + relationships to applications.
> > +
> > + See :ref:`media_controller`.
> > +
> > + MC-centric
> > + V4L2 hardware that requires a Media controller.
> > +
> > + See :ref:`v4l2_hardware_control`.
> > +
> > + Microprocessor
> > + An electronic circuitry that carries out the instructions
> > + of a computer program by performing the basic arithmetic, logical,
> > + control and input/output (I/O) operations specified by the
> > + instructions on a single integrated circuit.
> > +
> > + SMBus
> > + A subset of I²C, with defines a stricter usage of the bus.
> > +
> > + Serial Peripheral Interface Bus - SPI
> > + Synchronous serial communication interface specification used for
> > + short distance communication, primarily in embedded systems.
> > +
> > + System on a Chip - SoC
> > + An integrated circuit that integrates all components of a computer
> > + or other electronic systems.
> > +
> > + Sub-device hardware components
> > + Hardware components that aren't controlled by the
> > + V4L2 main driver.
>
> Do we really need this? If we do, then this description needs to be fixed:
> you only say what it isn't controller by, not what actually does control it.
>
> > +
> > + V4L2 device node
> > + A device node that is associated to a V4L2 main driver,
> > + as specified in :ref:`v4l2_device_naming`.
> > +
> > + V4L2 hardware
> > + A hardware used to on a media device supported by the V4L2
> > + subsystem.
> > +
> > + V4L2 hardware control
> > + The type of hardware control that a device supports.
> > +
> > + See :ref:`v4l2_hardware_control`.
>
> ??? This is the same as "Hardware peripheral control". I'd stick to just one
> term (i.e. "Media hardware control" as I proposed).
>
> > +
> > + V4L2 main driver
> > + The V4L2 device driver that implements the main logic to talk with
> > + the V4L2 hardware.
> > +
> > + Also known as bridge driver.
> > +
> > + See :ref:`v4l2_hardware_control`.
> > +
> > + V4L2 sub-device
> > + Part of the media hardware that it is implemented by a device
>
> it is -> is
>
> I don't think this is right. A V4L2 sub-device not hardware. It represents
> a media hardware component and is implemented in a V4L2 sub-device driver.
>
> > + driver that is not part of the main V4L2 driver.
> > +
> > + See :ref:`subdev`.
> > +
> > + Vdev-centric
>
> I strongly prefer to call this vdevnode-centric.
> 'vdev' is too vague and it only works for us because we use 'vdev' in our
> code as the name for a video device node structure. End-users has no knowledge
> of that.
>
> I agree with the text in patches 2-7, except for the terminology.
>
> If others agree, then once it is changed in a v7 patch series I'll review again
> for consistent usage of the terminology.

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

Regards,
Mauro


diff --git a/Documentation/media/uapi/v4l/glossary.rst b/Documentation/media/uapi/v4l/glossary.rst
index afafe1bc1894..b6767da1a46e 100644
--- a/Documentation/media/uapi/v4l/glossary.rst
+++ b/Documentation/media/uapi/v4l/glossary.rst
@@ -38,18 +38,12 @@ Glossary
A subset of the media hardware. For example an I²C or SPI device,
or an IP block inside an SoC or FPGA.

- Hardware peripheral
- A group of hardware components that together make a larger
- user-facing functional peripheral. For instance the SoC ISP IP
- cores and external camera sensors together make a
- camera hardware peripheral.
-
- Also known as peripheral.
-
- Hardware peripheral control
- Type of control for a hardware peripheral supported by V4L2 drivers.
-
- See :ref:`v4l2_hardware_control`.
+ Image Signal Processor - ISP
+ A specialised processor that implements a set of algorithms for
+ processing image data. ISPs may implement algorithms for lens
+ shading correction, demosaic, scaling and pixel format conversion
+ as well as produce statistics for the use of the control
+ algorithms (e.g. automatic exposure, white balance and focus).

Inter-Integrated Circuit - I²C
A multi-master, multi-slave, packet switched, single-ended,
@@ -63,10 +57,7 @@ Glossary

Also known as chip.

- IP block
- The same as IP core.
-
- Intelectual property core - IP core
+ Intellectual property core - IP core
In electronic design a semiconductor intellectual property core,
is a reusable unit of logic, cell, or integrated circuit layout
design that is the intellectual property of one party.
@@ -75,15 +66,13 @@ Glossary

See https://en.wikipedia.org/wiki/Semiconductor_intellectual_property_core).

- Image Signal Processor - ISP
- A specialised processor that implements a set of algorithms for
- processing image data. ISPs may implement algorithms for lens
- shading correction, demosaic, scaling and pixel format conversion
- as well as produce statistics for the use of the control
- algorithms (e.g. automatic exposure, white balance and focus).
+ IP block
+ The same as IP core.

- Peripheral
- The same as hardware peripheral.
+ MC-centric
+ V4L2 hardware that requires a Media controller.
+
+ See :ref:`v4l2_hardware_control`.

Media Controller
An API designed to expose and control devices and sub-devices
@@ -91,8 +80,14 @@ Glossary

See :ref:`media_controller`.

- MC-centric
- V4L2 hardware that requires a Media controller.
+ Media hardware
+ A group of hardware components that together make a larger
+ user-facing functional media hardware. For instance the SoC ISP IP
+ cores and external camera sensors together make a
+ camera media hardware.
+
+ Media hardware control
+ Type of control for a media hardware supported by V4L2 drivers.

See :ref:`v4l2_hardware_control`.

@@ -113,10 +108,6 @@ Glossary
An integrated circuit that integrates all components of a computer
or other electronic systems.

- Sub-device hardware components
- Hardware components that aren't controlled by the
- V4L2 main driver.
-
V4L2 device node
A device node that is associated to a V4L2 main driver,
as specified in :ref:`v4l2_device_naming`.
@@ -125,11 +116,6 @@ Glossary
A hardware used to on a media device supported by the V4L2
subsystem.

- V4L2 hardware control
- The type of hardware control that a device supports.
-
- See :ref:`v4l2_hardware_control`.
-
V4L2 main driver
The V4L2 device driver that implements the main logic to talk with
the V4L2 hardware.
@@ -139,12 +125,12 @@ Glossary
See :ref:`v4l2_hardware_control`.

V4L2 sub-device
- Part of the media hardware that it is implemented by a device
- driver that is not part of the main V4L2 driver.
+ Part of the media hardware that is implemented via a
+ V4L2 sub-device driver.

See :ref:`subdev`.

- Vdev-centric
+ Vdevnode-centric
V4L2 hardware that it is controlled via V4L2 device nodes.

See :ref:`v4l2_hardware_control`.
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 250f0b865943..ed011ed123cc 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -10,8 +10,8 @@ Opening and Closing Devices
.. _v4l2_hardware_control:


-Types of V4L2 hardware peripheral control
-=========================================
+Types of V4L2 media hardware control
+====================================

V4L2 hardware periferal is usually complex: support for it is
implemented via a V4L2 main driver and often by several additional drivers.
@@ -26,22 +26,22 @@ controlled directly by the main driver or explicitly via
the **V4L2 sub-device API** (see :ref:`subdev`).

When V4L2 was originally designed, there was only one type of
-peripheral control: via the **V4L2 device nodes**. We refer to this kind
-of control as **V4L2 device node centric** (or, simply, "**vdev-centric**").
+media hardware control: via the **V4L2 device nodes**. We refer to this kind
+of control as **V4L2 device node centric** (or, simply, "**vdevnode-centric**").

Later (kernel 2.6.39), a new type of periferal control was
-added in order to support complex peripherals that are common for embedded
+added in order to support complex media hardware that are common for embedded
systems. This type of periferal is controlled mainly via the media
controller and V4L2 sub-devices. So, it is called
**Media controller centric** (or, simply, "**MC-centric**") control.

-For **vdev-centric** hardware peripheral control, the peripheral is
+For **vdevnode-centric** media hardware control, the media hardware is
controlled via the **V4L2 device nodes**. They may optionally support the
:ref:`media controller API <media_controller>` as well,
in order to inform the application which device nodes are available
(see :ref:`related`).

-For **MC-centric** hardware peripheral control it is required to configure
+For **MC-centric** media hardware control it is required to configure
the pipelines via the :ref:`media controller API <media_controller>` before
the periferal can be used. For such devices, the sub-devices' configuration
can be controlled via the :ref:`sub-device API <subdev>`, which creates one
@@ -49,14 +49,14 @@ device node per sub-device.

.. note::

- A **vdev-centric** may also optionally expose V4L2 sub-devices via
+ A **vdevnode-centric** may also optionally expose V4L2 sub-devices via
:ref:`sub-device API <subdev>`. In that case, it has to implement
the :ref:`media controller API <media_controller>` as well.


.. attention::

- Devices that require **MC-centric** hardware peripheral control should
+ Devices that require **MC-centric** media hardware control should
report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
(see :ref:`VIDIOC_QUERYCAP`).

diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst
index cf69a5e33df2..944bc5ba484f 100644
--- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
+++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
@@ -257,7 +257,7 @@ specification the ioctl returns an ``EINVAL`` error code.
* - ``V4L2_MC_CENTRIC``
- 0x20000000
- Indicates that the device require **MC-centric** hardware
- control, and thus can't be used by **vdev-centric** applications.
+ control, and thus can't be used by **vdevnode-centric** applications.
See :ref:`v4l2_hardware_control` for more details.
* - ``V4L2_CAP_DEVICE_CAPS``
- 0x80000000


Thanks,
Mauro

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