Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 375 insertions, 0 deletions

diff --git a/Documentation/driver-api/media/v4l2-dev.rst b/Documentation/driver-api/media/v4l2-dev.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+Video device' s internal representation
+=======================================
+
+The actual device nodes in the ``/dev`` directory are created using the
+:c:type:`video_device` struct (``v4l2-dev.h``). This struct can either be
+allocated dynamically or embedded in a larger struct.
+
+To allocate it dynamically use :c:func:`video_device_alloc`:
+
+.. code-block:: c
+
+	struct video_device *vdev = video_device_alloc();
+
+	if (vdev == NULL)
+		return -ENOMEM;
+
+	vdev->release = video_device_release;
+
+If you embed it in a larger struct, then you must set the ``release()``
+callback to your own function:
+
+.. code-block:: c
+
+	struct video_device *vdev = &my_vdev->vdev;
+
+	vdev->release = my_vdev_release;
+
+The ``release()`` callback must be set and it is called when the last user
+of the video device exits.
+
+The default :c:func:`video_device_release` callback currently
+just calls ``kfree`` to free the allocated memory.
+
+There is also a :c:func:`video_device_release_empty` function that does
+nothing (is empty) and should be used if the struct is embedded and there
+is nothing to do when it is released.
+
+You should also set these fields of :c:type:`video_device`:
+
+- :c:type:`video_device`->v4l2_dev: must be set to the :c:type:`v4l2_device`
+  parent device.
+
+- :c:type:`video_device`->name: set to something descriptive and unique.
+
+- :c:type:`video_device`->vfl_dir: set this to ``VFL_DIR_RX`` for capture
+  devices (``VFL_DIR_RX`` has value 0, so this is normally already the
+  default), set to ``VFL_DIR_TX`` for output devices and ``VFL_DIR_M2M`` for mem2mem (codec) devices.
+
+- :c:type:`video_device`->fops: set to the :c:type:`v4l2_file_operations`
+  struct.
+
+- :c:type:`video_device`->ioctl_ops: if you use the :c:type:`v4l2_ioctl_ops`
+  to simplify ioctl maintenance (highly recommended to use this and it might
+  become compulsory in the future!), then set this to your
+  :c:type:`v4l2_ioctl_ops` struct. The :c:type:`video_device`->vfl_type and
+  :c:type:`video_device`->vfl_dir fields are used to disable ops that do not
+  match the type/dir combination. E.g. VBI ops are disabled for non-VBI nodes,
+  and output ops  are disabled for a capture device. This makes it possible to
+  provide just one :c:type:`v4l2_ioctl_ops` struct for both vbi and
+  video nodes.
+
+- :c:type:`video_device`->lock: leave to ``NULL`` if you want to do all the
+  locking  in the driver. Otherwise you give it a pointer to a struct
+  ``mutex_lock`` and before the :c:type:`video_device`->unlocked_ioctl
+  file operation is called this lock will be taken by the core and released
+  afterwards. See the next section for more details.
+
+- :c:type:`video_device`->queue: a pointer to the struct vb2_queue
+  associated with this device node.
+  If queue is not ``NULL``, and queue->lock is not ``NULL``, then queue->lock
+  is used for the queuing ioctls (``VIDIOC_REQBUFS``, ``CREATE_BUFS``,
+  ``QBUF``, ``DQBUF``,  ``QUERYBUF``, ``PREPARE_BUF``, ``STREAMON`` and
+  ``STREAMOFF``) instead of the lock above.
+  That way the :ref:`vb2 <vb2_framework>` queuing framework does not have
+  to wait for other ioctls.   This queue pointer is also used by the
+  :ref:`vb2 <vb2_framework>` helper functions to check for
+  queuing ownership (i.e. is the filehandle calling it allowed to do the
+  operation).
+
+- :c:type:`video_device`->prio: keeps track of the priorities. Used to
+  implement ``VIDIOC_G_PRIORITY`` and ``VIDIOC_S_PRIORITY``.
+  If left to ``NULL``, then it will use the struct v4l2_prio_state
+  in :c:type:`v4l2_device`. If you want to have a separate priority state per
+  (group of) device node(s),   then you can point it to your own struct
+  :c:type:`v4l2_prio_state`.
+
+- :c:type:`video_device`->dev_parent: you only set this if v4l2_device was
+  registered with ``NULL`` as the parent ``device`` struct. This only happens
+  in cases where one hardware device has multiple PCI devices that all share
+  the same :c:type:`v4l2_device` core.
+
+  The cx88 driver is an example of this: one core :c:type:`v4l2_device` struct,
+  but   it is used by both a raw video PCI device (cx8800) and a MPEG PCI device
+  (cx8802). Since the :c:type:`v4l2_device` cannot be associated with two PCI
+  devices at the same time it is setup without a parent device. But when the
+  struct video_device is initialized you **do** know which parent
+  PCI device to use and so you set ``dev_device`` to the correct PCI device.
+
+If you use :c:type:`v4l2_ioctl_ops`, then you should set
+:c:type:`video_device`->unlocked_ioctl to :c:func:`video_ioctl2` in your
+:c:type:`v4l2_file_operations` struct.
+
+In some cases you want to tell the core that a function you had specified in
+your :c:type:`v4l2_ioctl_ops` should be ignored. You can mark such ioctls by
+calling this function before :c:func:`video_register_device` is called:
+
+	:c:func:`v4l2_disable_ioctl <v4l2_disable_ioctl>`
+	(:c:type:`vdev <video_device>`, cmd).
+
+This tends to be needed if based on external factors (e.g. which card is
+being used) you want to turns off certain features in :c:type:`v4l2_ioctl_ops`
+without having to make a new struct.
+
+The :c:type:`v4l2_file_operations` struct is a subset of file_operations.
+The main difference is that the inode argument is omitted since it is never
+used.
+
+If integration with the media framework is needed, you must initialize the
+:c:type:`media_entity` struct embedded in the :c:type:`video_device` struct
+(entity field) by calling :c:func:`media_entity_pads_init`:
+
+.. code-block:: c
+
+	struct media_pad *pad = &my_vdev->pad;
+	int err;
+
+	err = media_entity_pads_init(&vdev->entity, 1, pad);
+
+The pads array must have been previously initialized. There is no need to
+manually set the struct media_entity type and name fields.
+
+A reference to the entity will be automatically acquired/released when the
+video device is opened/closed.
+
+ioctls and locking
+------------------
+
+The V4L core provides optional locking services. The main service is the
+lock field in struct video_device, which is a pointer to a mutex.
+If you set this pointer, then that will be used by unlocked_ioctl to
+serialize all ioctls.
+
+If you are using the :ref:`videobuf2 framework <vb2_framework>`, then there
+is a second lock that you can set: :c:type:`video_device`->queue->lock. If
+set, then this lock will be used instead of :c:type:`video_device`->lock
+to serialize all queuing ioctls (see the previous section
+for the full list of those ioctls).
+
+The advantage of using a different lock for the queuing ioctls is that for some
+drivers (particularly USB drivers) certain commands such as setting controls
+can take a long time, so you want to use a separate lock for the buffer queuing
+ioctls. That way your ``VIDIOC_DQBUF`` doesn't stall because the driver is busy
+changing the e.g. exposure of the webcam.
+
+Of course, you can always do all the locking yourself by leaving both lock
+pointers at ``NULL``.
+
+If you use the old :ref:`videobuf framework <vb_framework>` then you must
+pass the :c:type:`video_device`->lock to the videobuf queue initialize
+function: if videobuf has to wait for a frame to arrive, then it will
+temporarily unlock the lock and relock it afterwards. If your driver also
+waits in the code, then you should do the same to allow other
+processes to access the device node while the first process is waiting for
+something.
+
+In the case of :ref:`videobuf2 <vb2_framework>` you will need to implement the
+``wait_prepare()`` and ``wait_finish()`` callbacks to unlock/lock if applicable.
+If you use the ``queue->lock`` pointer, then you can use the helper functions
+:c:func:`vb2_ops_wait_prepare` and :c:func:`vb2_ops_wait_finish`.
+
+The implementation of a hotplug disconnect should also take the lock from
+:c:type:`video_device` before calling v4l2_device_disconnect. If you are also
+using :c:type:`video_device`->queue->lock, then you have to first lock
+:c:type:`video_device`->queue->lock followed by :c:type:`video_device`->lock.
+That way you can be sure no ioctl is running when you call
+:c:func:`v4l2_device_disconnect`.
+
+Video device registration
+-------------------------
+
+Next you register the video device with :c:func:`video_register_device`.
+This will create the character device for you.
+
+.. code-block:: c
+
+	err = video_register_device(vdev, VFL_TYPE_VIDEO, -1);
+	if (err) {
+		video_device_release(vdev); /* or kfree(my_vdev); */
+		return err;
+	}
+
+If the :c:type:`v4l2_device` parent device has a not ``NULL`` mdev field,
+the video device entity will be automatically registered with the media
+device.
+
+Which device is registered depends on the type argument. The following
+types exist:
+
+========================== ====================	 ==============================
+:c:type:`vfl_devnode_type` Device name		 Usage
+========================== ====================	 ==============================
+``VFL_TYPE_VIDEO``         ``/dev/videoX``       for video input/output devices
+``VFL_TYPE_VBI``           ``/dev/vbiX``         for vertical blank data (i.e.
+						 closed captions, teletext)
+``VFL_TYPE_RADIO``         ``/dev/radioX``       for radio tuners
+``VFL_TYPE_SUBDEV``        ``/dev/v4l-subdevX``  for V4L2 subdevices
+``VFL_TYPE_SDR``           ``/dev/swradioX``     for Software Defined Radio
+						 (SDR) tuners
+``VFL_TYPE_TOUCH``         ``/dev/v4l-touchX``   for touch sensors
+========================== ====================	 ==============================
+
+The last argument gives you a certain amount of control over the device
+node number used (i.e. the X in ``videoX``). Normally you will pass -1
+to let the v4l2 framework pick the first free number. But sometimes users
+want to select a specific node number. It is common that drivers allow
+the user to select a specific device node number through a driver module
+option. That number is then passed to this function and video_register_device
+will attempt to select that device node number. If that number was already
+in use, then the next free device node number will be selected and it
+will send a warning to the kernel log.
+
+Another use-case is if a driver creates many devices. In that case it can
+be useful to place different video devices in separate ranges. For example,
+video capture devices start at 0, video output devices start at 16.
+So you can use the last argument to specify a minimum device node number
+and the v4l2 framework will try to pick the first free number that is equal
+or higher to what you passed. If that fails, then it will just pick the
+first free number.
+
+Since in this case you do not care about a warning about not being able
+to select the specified device node number, you can call the function
+:c:func:`video_register_device_no_warn` instead.
+
+Whenever a device node is created some attributes are also created for you.
+If you look in ``/sys/class/video4linux`` you see the devices. Go into e.g.
+``video0`` and you will see 'name', 'dev_debug' and 'index' attributes. The
+'name' attribute is the 'name' field of the video_device struct. The
+'dev_debug' attribute can be used to enable core debugging. See the next
+section for more detailed information on this.
+
+The 'index' attribute is the index of the device node: for each call to
+:c:func:`video_register_device()` the index is just increased by 1. The
+first video device node you register always starts with index 0.
+
+Users can setup udev rules that utilize the index attribute to make fancy
+device names (e.g. '``mpegX``' for MPEG video capture device nodes).
+
+After the device was successfully registered, then you can use these fields:
+
+- :c:type:`video_device`->vfl_type: the device type passed to
+  :c:func:`video_register_device`.
+- :c:type:`video_device`->minor: the assigned device minor number.
+- :c:type:`video_device`->num: the device node number (i.e. the X in
+  ``videoX``).
+- :c:type:`video_device`->index: the device index number.
+
+If the registration failed, then you need to call
+:c:func:`video_device_release` to free the allocated :c:type:`video_device`
+struct, or free your own struct if the :c:type:`video_device` was embedded in
+it. The ``vdev->release()`` callback will never be called if the registration
+failed, nor should you ever attempt to unregister the device if the
+registration failed.
+
+video device debugging
+----------------------
+
+The 'dev_debug' attribute that is created for each video, vbi, radio or swradio
+device in ``/sys/class/video4linux/<devX>/`` allows you to enable logging of
+file operations.
+
+It is a bitmask and the following bits can be set:
+
+.. tabularcolumns:: |p{5ex}|L|
+
+===== ================================================================
+Mask  Description
+===== ================================================================
+0x01  Log the ioctl name and error code. VIDIOC_(D)QBUF ioctls are
+      only logged if bit 0x08 is also set.
+0x02  Log the ioctl name arguments and error code. VIDIOC_(D)QBUF
+      ioctls are
+      only logged if bit 0x08 is also set.
+0x04  Log the file operations open, release, read, write, mmap and
+      get_unmapped_area. The read and write operations are only
+      logged if bit 0x08 is also set.
+0x08  Log the read and write file operations and the VIDIOC_QBUF and
+      VIDIOC_DQBUF ioctls.
+0x10  Log the poll file operation.
+0x20  Log error and messages in the control operations.
+===== ================================================================
+
+Video device cleanup
+--------------------
+
+When the video device nodes have to be removed, either during the unload
+of the driver or because the USB device was disconnected, then you should
+unregister them with:
+
+	:c:func:`video_unregister_device`
+	(:c:type:`vdev <video_device>`);
+
+This will remove the device nodes from sysfs (causing udev to remove them
+from ``/dev``).
+
+After :c:func:`video_unregister_device` returns no new opens can be done.
+However, in the case of USB devices some application might still have one of
+these device nodes open. So after the unregister all file operations (except
+release, of course) will return an error as well.
+
+When the last user of the video device node exits, then the ``vdev->release()``
+callback is called and you can do the final cleanup there.
+
+Don't forget to cleanup the media entity associated with the video device if
+it has been initialized:
+
+	:c:func:`media_entity_cleanup <media_entity_cleanup>`
+	(&vdev->entity);
+
+This can be done from the release callback.
+
+
+helper functions
+----------------
+
+There are a few useful helper functions:
+
+- file and :c:type:`video_device` private data
+
+You can set/get driver private data in the video_device struct using:
+
+	:c:func:`video_get_drvdata <video_get_drvdata>`
+	(:c:type:`vdev <video_device>`);
+
+	:c:func:`video_set_drvdata <video_set_drvdata>`
+	(:c:type:`vdev <video_device>`);
+
+Note that you can safely call :c:func:`video_set_drvdata` before calling
+:c:func:`video_register_device`.
+
+And this function:
+
+	:c:func:`video_devdata <video_devdata>`
+	(struct file \*file);
+
+returns the video_device belonging to the file struct.
+
+The :c:func:`video_devdata` function combines :c:func:`video_get_drvdata`
+with :c:func:`video_devdata`:
+
+	:c:func:`video_drvdata <video_drvdata>`
+	(struct file \*file);
+
+You can go from a :c:type:`video_device` struct to the v4l2_device struct using:
+
+.. code-block:: c
+
+	struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
+
+- Device node name
+
+The :c:type:`video_device` node kernel name can be retrieved using:
+
+	:c:func:`video_device_node_name <video_device_node_name>`
+	(:c:type:`vdev <video_device>`);
+
+The name is used as a hint by userspace tools such as udev. The function
+should be used where possible instead of accessing the video_device::num and
+video_device::minor fields.
+
+video_device functions and data structures
+------------------------------------------
+
+.. kernel-doc:: include/media/v4l2-dev.h