Merge tag 'media/v5.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media

Pull media updates from Mauro Carvalho Chehab:

 - Media documentation is now split into admin-guide, driver-api and
   userspace-api books (a longstanding request from Jon);

 - The media Kconfig was reorganized, in order to make easier to select
   drivers and their dependencies;

 - The testing drivers now has a separate directory;

 - added a new driver for Rockchip Video Decoder IP;

 - The atomisp staging driver was resurrected. It is meant to work with
   4 generations of cameras on Atom-based laptops, tablets and cell
   phones. So, it seems worth investing time to cleanup this driver and
   making it in good shape.

 - Added some V4L2 core ancillary routines to help with h264 codecs;

 - Added an ov2740 image sensor driver;

 - The si2157 gained support for Analog TV, which, in turn, added
   support for some cx231xx and cx23885 boards to also support analog
   standards;

 - Added some V4L2 controls (V4L2_CID_CAMERA_ORIENTATION and
   V4L2_CID_CAMERA_SENSOR_ROTATION) to help identifying where the camera
   is located at the device;

 - VIDIOC_ENUM_FMT was extended to support MC-centric devices;

 - Lots of drivers improvements and cleanups.

* tag 'media/v5.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (503 commits)
  media: Documentation: media: Refer to mbus format documentation from CSI-2 docs
  media: s5k5baf: Replace zero-length array with flexible-array
  media: i2c: imx219: Drop <linux/clk-provider.h> and <linux/clkdev.h>
  media: i2c: Add ov2740 image sensor driver
  media: ov8856: Implement sensor module revision identification
  media: ov8856: Add devicetree support
  media: dt-bindings: ov8856: Document YAML bindings
  media: dvb-usb: Add Cinergy S2 PCIe Dual Port support
  media: dvbdev: Fix tuner->demod media controller link
  media: dt-bindings: phy: phy-rockchip-dphy-rx0: move rockchip dphy rx0 bindings out of staging
  media: staging: dt-bindings: phy-rockchip-dphy-rx0: remove non-used reg property
  media: atomisp: unify the version for isp2401 a0 and b0 versions
  media: atomisp: update TODO with the current data
  media: atomisp: adjust some code at sh_css that could be broken
  media: atomisp: don't produce errs for ignored IRQs
  media: atomisp: print IRQ when debugging
  media: atomisp: isp_mmu: don't use kmem_cache
  media: atomisp: add a notice about possible leak resources
  media: atomisp: disable the dynamic and reserved pools
  media: atomisp: turn on camera before setting it
  ...

1 files changed, 165 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst
new file mode 100644
index 000000000000..38046ef20141
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/open.rst
@@ -0,0 +1,165 @@
+.. 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.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _open:
+
+***************************
+Opening and Closing Devices
+***************************
+
+
+Device Naming
+=============
+
+V4L2 drivers are implemented as kernel modules, loaded manually by the
+system administrator or automatically when a device is first discovered.
+The driver modules plug into the "videodev" kernel module. It provides
+helper functions and a common application interface specified in this
+document.
+
+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.).
+
+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:
+
+.. code-block:: none
+
+   # modprobe mydriver video_nr=0,1 radio_nr=0,1
+
+In ``/etc/modules.conf`` this may be written as:
+
+::
+
+    options mydriver video_nr=0,1 radio_nr=0,1
+
+When no device node number is given as module option the driver supplies
+a default.
+
+Normally udev will create the device nodes in /dev automatically for
+you. If udev is not installed, then you need to enable the
+CONFIG_VIDEO_FIXED_MINOR_RANGES kernel option in order to be able to
+correctly relate a minor number to a device node number. I.e., you need
+to be certain that minor number 5 maps to device node name video5. With
+this kernel option different device types have different minor number
+ranges. These ranges are listed in :ref:`devices`.
+
+The creation of character special files (with mknod) is a privileged
+operation and devices cannot be opened by major and minor number. That
+means applications cannot *reliably* scan for loaded or installed
+drivers. The user must enter a device name, or the application can try
+the conventional device names.
+
+
+.. _related:
+
+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 was designed with the idea that one device node could
+support all functions. However, in practice this never worked: this
+'feature' was never used by applications and many drivers did not
+support it and if they did it was certainly never tested. In addition,
+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.
+
+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
+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
+towards both Media Controller-based devices and devices that do not use
+the Media Controller. If you want to work on this please write to the
+linux-media mailing list:
+`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__.
+
+
+Multiple Opens
+==============
+
+V4L2 devices can be opened more than once. [#f1]_ When this is supported
+by the driver, users can for example start a "panel" application to
+change controls like brightness or audio volume, while another
+application captures video and audio. In other words, panel applications
+are comparable to an ALSA audio mixer application. Just opening a V4L2
+device should not change the state of the device. [#f2]_
+
+Once an application has allocated the memory buffers needed for
+streaming data (by calling the :ref:`VIDIOC_REQBUFS`
+or :ref:`VIDIOC_CREATE_BUFS` ioctls, or
+implicitly by calling the :ref:`read() <func-read>` or
+:ref:`write() <func-write>` functions) that application (filehandle)
+becomes the owner of the device. It is no longer allowed to make changes
+that would affect the buffer sizes (e.g. by calling the
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl) and other applications are
+no longer allowed to allocate buffers or start or stop streaming. The
+EBUSY error code will be returned instead.
+
+Merely opening a V4L2 device does not grant exclusive access. [#f3]_
+Initiating data exchange however assigns the right to read or write the
+requested type of data, and to change related properties, to this file
+descriptor. Applications can request additional access privileges using
+the priority mechanism described in :ref:`app-pri`.
+
+
+Shared Data Streams
+===================
+
+V4L2 drivers should not support multiple applications reading or writing
+the same data stream on a device by copying buffers, time multiplexing
+or similar means. This is better handled by a proxy application in user
+space.
+
+
+Functions
+=========
+
+To open and close V4L2 devices applications use the
+:ref:`open() <func-open>` and :ref:`close() <func-close>` function,
+respectively. Devices are programmed using the
+:ref:`ioctl() <func-ioctl>` function as explained in the following
+sections.
+
+.. [#f1]
+   There are still some old and obscure drivers that have not been
+   updated to allow for multiple opens. This implies that for such
+   drivers :ref:`open() <func-open>` can return an ``EBUSY`` error code
+   when the device is already in use.
+
+.. [#f2]
+   Unfortunately, opening a radio device often switches the state of the
+   device to radio mode in many drivers. This behavior should be fixed
+   eventually as it violates the V4L2 specification.
+
+.. [#f3]
+   Drivers could recognize the ``O_EXCL`` open flag. Presently this is
+   not required, so applications cannot know if it really works.