diff options
Diffstat (limited to 'Documentation/driver-api/media/v4l2-dev.rst')
| -rw-r--r-- | Documentation/driver-api/media/v4l2-dev.rst | 18 |
1 files changed, 5 insertions, 13 deletions
diff --git a/Documentation/driver-api/media/v4l2-dev.rst b/Documentation/driver-api/media/v4l2-dev.rst index 63c064837c00..d5cb19b21a9f 100644 --- a/Documentation/driver-api/media/v4l2-dev.rst +++ b/Documentation/driver-api/media/v4l2-dev.rst @@ -67,7 +67,7 @@ You should also set these fields of :c:type:`video_device`: 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 :c:type:`vb2_queue` +- :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``, @@ -81,7 +81,7 @@ You should also set these fields of :c:type:`video_device`: - :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 :c:type:`v4l2_prio_state` + 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`. @@ -95,7 +95,7 @@ You should also set these fields of :c:type:`video_device`: 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 :c:type:`video_device` is initialized you **do** know which parent + 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 @@ -138,7 +138,7 @@ ioctls and locking ------------------ The V4L core provides optional locking services. The main service is the -lock field in struct :c:type:`video_device`, which is a pointer to a mutex. +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. @@ -157,14 +157,6 @@ 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 @@ -212,7 +204,7 @@ types exist: ========================== ==================== ============================== The last argument gives you a certain amount of control over the device -device node number used (i.e. the X in ``videoX``). Normally you will pass -1 +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 |