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, 140 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/func-read.rst b/Documentation/userspace-api/media/v4l/func-read.rst
new file mode 100644
index 000000000000..1728aa5d8313
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/func-read.rst
@@ -0,0 +1,140 @@
+.. 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
+
+.. _func-read:
+
+***********
+V4L2 read()
+***********
+
+Name
+====
+
+v4l2-read - Read from a V4L2 device
+
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <unistd.h>
+
+
+.. c:function:: ssize_t read( int fd, void *buf, size_t count )
+    :name: v4l2-read
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``buf``
+   Buffer to be filled
+
+``count``
+  Max number of bytes to read
+
+Description
+===========
+
+:ref:`read() <func-read>` attempts to read up to ``count`` bytes from file
+descriptor ``fd`` into the buffer starting at ``buf``. The layout of the
+data in the buffer is discussed in the respective device interface
+section, see ##. If ``count`` is zero, :ref:`read() <func-read>` returns zero
+and has no other results. If ``count`` is greater than ``SSIZE_MAX``,
+the result is unspecified. Regardless of the ``count`` value each
+:ref:`read() <func-read>` call will provide at most one frame (two fields)
+worth of data.
+
+By default :ref:`read() <func-read>` blocks until data becomes available. When
+the ``O_NONBLOCK`` flag was given to the :ref:`open() <func-open>`
+function it returns immediately with an ``EAGAIN`` error code when no data
+is available. The :ref:`select() <func-select>` or
+:ref:`poll() <func-poll>` functions can always be used to suspend
+execution until data becomes available. All drivers supporting the
+:ref:`read() <func-read>` function must also support :ref:`select() <func-select>` and
+:ref:`poll() <func-poll>`.
+
+Drivers can implement read functionality in different ways, using a
+single or multiple buffers and discarding the oldest or newest frames
+once the internal buffers are filled.
+
+:ref:`read() <func-read>` never returns a "snapshot" of a buffer being filled.
+Using a single buffer the driver will stop capturing when the
+application starts reading the buffer until the read is finished. Thus
+only the period of the vertical blanking interval is available for
+reading, or the capture rate must fall below the nominal frame rate of
+the video standard.
+
+The behavior of :ref:`read() <func-read>` when called during the active picture
+period or the vertical blanking separating the top and bottom field
+depends on the discarding policy. A driver discarding the oldest frames
+keeps capturing into an internal buffer, continuously overwriting the
+previously, not read frame, and returns the frame being received at the
+time of the :ref:`read() <func-read>` call as soon as it is complete.
+
+A driver discarding the newest frames stops capturing until the next
+:ref:`read() <func-read>` call. The frame being received at :ref:`read() <func-read>`
+time is discarded, returning the following frame instead. Again this
+implies a reduction of the capture rate to one half or less of the
+nominal frame rate. An example of this model is the video read mode of
+the bttv driver, initiating a DMA to user memory when :ref:`read() <func-read>`
+is called and returning when the DMA finished.
+
+In the multiple buffer model drivers maintain a ring of internal
+buffers, automatically advancing to the next free buffer. This allows
+continuous capturing when the application can empty the buffers fast
+enough. Again, the behavior when the driver runs out of free buffers
+depends on the discarding policy.
+
+Applications can get and set the number of buffers used internally by
+the driver with the :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
+:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctls. They are optional,
+however. The discarding policy is not reported and cannot be changed.
+For minimum requirements see :ref:`devices`.
+
+
+Return Value
+============
+
+On success, the number of bytes read is returned. It is not an error if
+this number is smaller than the number of bytes requested, or the amount
+of data required for one frame. This may happen for example because
+:ref:`read() <func-read>` was interrupted by a signal. On error, -1 is
+returned, and the ``errno`` variable is set appropriately. In this case
+the next read will start at the beginning of a new frame. Possible error
+codes are:
+
+EAGAIN
+    Non-blocking I/O has been selected using O_NONBLOCK and no data was
+    immediately available for reading.
+
+EBADF
+    ``fd`` is not a valid file descriptor or is not open for reading, or
+    the process already has the maximum number of files open.
+
+EBUSY
+    The driver does not support multiple read streams and the device is
+    already in use.
+
+EFAULT
+    ``buf`` references an inaccessible memory area.
+
+EINTR
+    The call was interrupted by a signal before any data was read.
+
+EIO
+    I/O error. This indicates some hardware problem or a failure to
+    communicate with a remote device (USB camera etc.).
+
+EINVAL
+    The :ref:`read() <func-read>` function is not supported by this driver, not
+    on this device, or generally not on this type of device.