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Diffstat (limited to 'Documentation/media/kapi/v4l2-framework.rst')
-rw-r--r-- | Documentation/media/kapi/v4l2-framework.rst | 133 |
1 files changed, 0 insertions, 133 deletions
diff --git a/Documentation/media/kapi/v4l2-framework.rst b/Documentation/media/kapi/v4l2-framework.rst index d46380ac7c1d..8b4f684e1a7a 100644 --- a/Documentation/media/kapi/v4l2-framework.rst +++ b/Documentation/media/kapi/v4l2-framework.rst @@ -80,139 +80,6 @@ The V4L2 framework also optionally integrates with the media framework. If a driver sets the struct v4l2_device mdev field, sub-devices and video nodes will automatically appear in the media framework as entities. -struct v4l2_fh --------------- - -struct v4l2_fh provides a way to easily keep file handle specific data -that is used by the V4L2 framework. New drivers must use struct v4l2_fh -since it is also used to implement priority handling (VIDIOC_G/S_PRIORITY). - -The users of v4l2_fh (in the V4L2 framework, not the driver) know -whether a driver uses v4l2_fh as its file->private_data pointer by -testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. This bit is -set whenever v4l2_fh_init() is called. - -struct v4l2_fh is allocated as a part of the driver's own file handle -structure and file->private_data is set to it in the driver's open -function by the driver. - -In many cases the struct v4l2_fh will be embedded in a larger structure. -In that case you should call v4l2_fh_init+v4l2_fh_add in open() and -v4l2_fh_del+v4l2_fh_exit in release(). - -Drivers can extract their own file handle structure by using the container_of -macro. Example: - -.. code-block:: none - - struct my_fh { - int blah; - struct v4l2_fh fh; - }; - - ... - - int my_open(struct file *file) - { - struct my_fh *my_fh; - struct video_device *vfd; - int ret; - - ... - - my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL); - - ... - - v4l2_fh_init(&my_fh->fh, vfd); - - ... - - file->private_data = &my_fh->fh; - v4l2_fh_add(&my_fh->fh); - return 0; - } - - int my_release(struct file *file) - { - struct v4l2_fh *fh = file->private_data; - struct my_fh *my_fh = container_of(fh, struct my_fh, fh); - - ... - v4l2_fh_del(&my_fh->fh); - v4l2_fh_exit(&my_fh->fh); - kfree(my_fh); - return 0; - } - -Below is a short description of the v4l2_fh functions used: - -.. code-block:: none - - void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev) - - Initialise the file handle. This *MUST* be performed in the driver's - v4l2_file_operations->open() handler. - -.. code-block:: none - - void v4l2_fh_add(struct v4l2_fh *fh) - - Add a v4l2_fh to video_device file handle list. Must be called once the - file handle is completely initialized. - -.. code-block:: none - - void v4l2_fh_del(struct v4l2_fh *fh) - - Unassociate the file handle from video_device(). The file handle - exit function may now be called. - -.. code-block:: none - - void v4l2_fh_exit(struct v4l2_fh *fh) - - Uninitialise the file handle. After uninitialisation the v4l2_fh - memory can be freed. - - -If struct v4l2_fh is not embedded, then you can use these helper functions: - -.. code-block:: none - - int v4l2_fh_open(struct file *filp) - - This allocates a struct v4l2_fh, initializes it and adds it to the struct - video_device associated with the file struct. - -.. code-block:: none - - int v4l2_fh_release(struct file *filp) - - This deletes it from the struct video_device associated with the file - struct, uninitialised the v4l2_fh and frees it. - -These two functions can be plugged into the v4l2_file_operation's open() and -release() ops. - - -Several drivers need to do something when the first file handle is opened and -when the last file handle closes. Two helper functions were added to check -whether the v4l2_fh struct is the only open filehandle of the associated -device node: - -.. code-block:: none - - int v4l2_fh_is_singular(struct v4l2_fh *fh) - - Returns 1 if the file handle is the only open file handle, else 0. - -.. code-block:: none - - int v4l2_fh_is_singular_file(struct file *filp) - - Same, but it calls v4l2_fh_is_singular with filp->private_data. - V4L2 clocks ----------- |