[media] doc-rst: do a poor man's conversion of v4l2-framework
Make Sphinx happy with v4l2-framework.rst by putting all C code inside code-block. Please note that this is a poor man ReST conversion, as several of those blocks should actually be converted to use :cpp:func:, pointing to the kAPI auto-generated documentation. The problem is that we currently lack kernel-doc documentation for most of the stuff described there. So, let's do a poor man's conversion. We should later address this. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab
parent
f6ebc2d341
commit
4c21d4fb1b
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@ -57,6 +57,8 @@ All drivers have the following structure:
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This is a rough schematic of how it all relates:
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.. code-block:: none
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device instances
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+-sub-device instances
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@ -88,6 +90,8 @@ would embed this struct inside a larger struct.
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You must register the device instance:
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.. code-block:: none
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v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
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Registration will initialize the v4l2_device struct. If the dev->driver_data
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@ -103,7 +107,7 @@ and registered media_device instance.
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If v4l2_dev->name is empty then it will be set to a value derived from dev
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(driver name followed by the bus_id, to be precise). If you set it up before
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calling v4l2_device_register then it will be untouched. If dev is NULL, then
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you *must* setup v4l2_dev->name before calling v4l2_device_register.
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you **must** setup v4l2_dev->name before calling v4l2_device_register.
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You can use v4l2_device_set_name() to set the name based on a driver name and
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a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1,
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@ -122,6 +126,8 @@ include/media/<subdevice>.h.
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You unregister with:
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.. code-block:: none
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v4l2_device_unregister(struct v4l2_device *v4l2_dev);
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If the dev->driver_data field points to v4l2_dev, it will be reset to NULL.
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@ -132,6 +138,8 @@ happens the parent device becomes invalid. Since v4l2_device has a pointer to
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that parent device it has to be cleared as well to mark that the parent is
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gone. To do this call:
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.. code-block:: none
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v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
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This does *not* unregister the subdevs, so you still need to call the
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@ -145,43 +153,47 @@ hardware. The same is true for alsa drivers for example.
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You can iterate over all registered devices as follows:
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static int callback(struct device *dev, void *p)
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{
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struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
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.. code-block:: none
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/* test if this device was inited */
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if (v4l2_dev == NULL)
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static int callback(struct device *dev, void *p)
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{
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struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
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/* test if this device was inited */
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if (v4l2_dev == NULL)
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return 0;
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...
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return 0;
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...
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return 0;
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}
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}
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int iterate(void *p)
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{
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struct device_driver *drv;
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int err;
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int iterate(void *p)
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{
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struct device_driver *drv;
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int err;
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/* Find driver 'ivtv' on the PCI bus.
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pci_bus_type is a global. For USB busses use usb_bus_type. */
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drv = driver_find("ivtv", &pci_bus_type);
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/* iterate over all ivtv device instances */
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err = driver_for_each_device(drv, NULL, p, callback);
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put_driver(drv);
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return err;
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}
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/* Find driver 'ivtv' on the PCI bus.
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pci_bus_type is a global. For USB busses use usb_bus_type. */
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drv = driver_find("ivtv", &pci_bus_type);
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/* iterate over all ivtv device instances */
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err = driver_for_each_device(drv, NULL, p, callback);
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put_driver(drv);
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return err;
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}
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Sometimes you need to keep a running counter of the device instance. This is
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commonly used to map a device instance to an index of a module option array.
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The recommended approach is as follows:
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static atomic_t drv_instance = ATOMIC_INIT(0);
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.. code-block:: none
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static int drv_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
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{
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...
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state->instance = atomic_inc_return(&drv_instance) - 1;
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}
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static atomic_t drv_instance = ATOMIC_INIT(0);
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static int drv_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
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{
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...
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state->instance = atomic_inc_return(&drv_instance) - 1;
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}
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If you have multiple device nodes then it can be difficult to know when it is
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safe to unregister v4l2_device for hotpluggable devices. For this purpose
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@ -193,11 +205,15 @@ callback is called. You can do your final cleanup there.
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If other device nodes (e.g. ALSA) are created, then you can increase and
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decrease the refcount manually as well by calling:
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void v4l2_device_get(struct v4l2_device *v4l2_dev);
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.. code-block:: none
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void v4l2_device_get(struct v4l2_device *v4l2_dev);
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or:
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int v4l2_device_put(struct v4l2_device *v4l2_dev);
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.. code-block:: none
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int v4l2_device_put(struct v4l2_device *v4l2_dev);
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Since the initial refcount is 1 you also need to call v4l2_device_put in the
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disconnect() callback (for USB devices) or in the remove() callback (for e.g.
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@ -249,35 +265,37 @@ may be NULL if the subdev driver does not support anything from that category.
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It looks like this:
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struct v4l2_subdev_core_ops {
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int (*log_status)(struct v4l2_subdev *sd);
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int (*init)(struct v4l2_subdev *sd, u32 val);
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...
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};
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.. code-block:: none
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struct v4l2_subdev_tuner_ops {
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...
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};
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struct v4l2_subdev_core_ops {
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int (*log_status)(struct v4l2_subdev *sd);
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int (*init)(struct v4l2_subdev *sd, u32 val);
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...
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};
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struct v4l2_subdev_audio_ops {
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...
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};
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struct v4l2_subdev_tuner_ops {
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...
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};
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struct v4l2_subdev_video_ops {
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...
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};
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struct v4l2_subdev_audio_ops {
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...
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};
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struct v4l2_subdev_pad_ops {
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...
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};
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struct v4l2_subdev_video_ops {
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...
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};
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struct v4l2_subdev_ops {
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const struct v4l2_subdev_core_ops *core;
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const struct v4l2_subdev_tuner_ops *tuner;
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const struct v4l2_subdev_audio_ops *audio;
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const struct v4l2_subdev_video_ops *video;
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const struct v4l2_subdev_pad_ops *video;
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};
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struct v4l2_subdev_pad_ops {
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...
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};
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struct v4l2_subdev_ops {
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const struct v4l2_subdev_core_ops *core;
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const struct v4l2_subdev_tuner_ops *tuner;
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const struct v4l2_subdev_audio_ops *audio;
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const struct v4l2_subdev_video_ops *video;
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const struct v4l2_subdev_pad_ops *video;
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};
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The core ops are common to all subdevs, the other categories are implemented
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depending on the sub-device. E.g. a video device is unlikely to support the
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@ -288,6 +306,8 @@ to add new ops and categories.
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A sub-device driver initializes the v4l2_subdev struct using:
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.. code-block:: none
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v4l2_subdev_init(sd, &ops);
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Afterwards you need to initialize subdev->name with a unique name and set the
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@ -297,6 +317,8 @@ If integration with the media framework is needed, you must initialize the
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media_entity struct embedded in the v4l2_subdev struct (entity field) by
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calling media_entity_pads_init(), if the entity has pads:
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.. code-block:: none
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struct media_pad *pads = &my_sd->pads;
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int err;
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@ -311,6 +333,8 @@ subdev device node (if any) is opened/closed.
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Don't forget to cleanup the media entity before the sub-device is destroyed:
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.. code-block:: none
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media_entity_cleanup(&sd->entity);
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If the subdev driver intends to process video and integrate with the media
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@ -351,6 +375,8 @@ run-time bridge-subdevice interaction is in both cases the same.
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In the synchronous case a device (bridge) driver needs to register the
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v4l2_subdev with the v4l2_device:
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.. code-block:: none
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int err = v4l2_device_register_subdev(v4l2_dev, sd);
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This can fail if the subdev module disappeared before it could be registered.
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@ -362,16 +388,22 @@ entity will be automatically registered with the media device.
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You can unregister a sub-device using:
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.. code-block:: none
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v4l2_device_unregister_subdev(sd);
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Afterwards the subdev module can be unloaded and sd->dev == NULL.
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You can call an ops function either directly:
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.. code-block:: none
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err = sd->ops->core->g_std(sd, &norm);
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but it is better and easier to use this macro:
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.. code-block:: none
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err = v4l2_subdev_call(sd, core, g_std, &norm);
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The macro will to the right NULL pointer checks and returns -ENODEV if subdev
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@ -380,11 +412,15 @@ NULL, or the actual result of the subdev->ops->core->g_std ops.
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It is also possible to call all or a subset of the sub-devices:
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.. code-block:: none
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v4l2_device_call_all(v4l2_dev, 0, core, g_std, &norm);
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Any subdev that does not support this ops is skipped and error results are
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ignored. If you want to check for errors use this:
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.. code-block:: none
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err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_std, &norm);
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Any error except -ENOIOCTLCMD will exit the loop with that error. If no
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@ -509,13 +545,17 @@ you can just create a v4l2_subdev directly.
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A typical state struct would look like this (where 'chipname' is replaced by
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the name of the chip):
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struct chipname_state {
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struct v4l2_subdev sd;
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... /* additional state fields */
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};
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.. code-block:: none
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struct chipname_state {
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struct v4l2_subdev sd;
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... /* additional state fields */
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};
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Initialize the v4l2_subdev struct as follows:
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.. code-block:: none
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v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
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This function will fill in all the fields of v4l2_subdev and ensure that the
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@ -524,17 +564,23 @@ v4l2_subdev and i2c_client both point to one another.
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You should also add a helper inline function to go from a v4l2_subdev pointer
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to a chipname_state struct:
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static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
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{
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return container_of(sd, struct chipname_state, sd);
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}
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.. code-block:: none
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static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
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{
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return container_of(sd, struct chipname_state, sd);
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}
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Use this to go from the v4l2_subdev struct to the i2c_client struct:
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.. code-block:: none
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struct i2c_client *client = v4l2_get_subdevdata(sd);
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And this to go from an i2c_client to a v4l2_subdev struct:
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.. code-block:: none
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struct v4l2_subdev *sd = i2c_get_clientdata(client);
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Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback
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@ -550,8 +596,10 @@ from the remove() callback ensures that this is always done correctly.
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The bridge driver also has some helper functions it can use:
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
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"module_foo", "chipid", 0x36, NULL);
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
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"module_foo", "chipid", 0x36, NULL);
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This loads the given module (can be NULL if no module needs to be loaded) and
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calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
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@ -581,15 +629,17 @@ are probed.
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For example: this will probe for address 0x10:
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
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"module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
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"module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
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v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed
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to the i2c driver and replaces the irq, platform_data and addr arguments.
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If the subdev supports the s_config core ops, then that op is called with
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the irq and platform_data arguments after the subdev was setup. The older
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v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with
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v4l2_i2c_new_(probed\_)subdev functions will call s_config as well, but with
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irq set to 0 and platform_data set to NULL.
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struct video_device
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@ -601,6 +651,8 @@ dynamically or embedded in a larger struct.
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To allocate it dynamically use:
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.. code-block:: none
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struct video_device *vdev = video_device_alloc();
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if (vdev == NULL)
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@ -611,6 +663,8 @@ To allocate it dynamically use:
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If you embed it in a larger struct, then you must set the release()
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callback to your own function:
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.. code-block:: none
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struct video_device *vdev = &my_vdev->vdev;
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vdev->release = my_vdev_release;
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@ -684,7 +738,9 @@ In some cases you want to tell the core that a function you had specified in
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your v4l2_ioctl_ops should be ignored. You can mark such ioctls by calling this
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function before video_device_register is called:
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void v4l2_disable_ioctl(struct video_device *vdev, unsigned int cmd);
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.. code-block:: none
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void v4l2_disable_ioctl(struct video_device *vdev, unsigned int cmd);
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This tends to be needed if based on external factors (e.g. which card is
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being used) you want to turns off certain features in v4l2_ioctl_ops without
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@ -697,6 +753,8 @@ If integration with the media framework is needed, you must initialize the
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media_entity struct embedded in the video_device struct (entity field) by
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calling media_entity_pads_init():
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.. code-block:: none
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struct media_pad *pad = &my_vdev->pad;
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int err;
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@ -752,6 +810,8 @@ video_device registration
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Next you register the video device: this will create the character device
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for you.
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.. code-block:: none
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err = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
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if (err) {
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video_device_release(vdev); /* or kfree(my_vdev); */
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@ -827,16 +887,18 @@ file operations.
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It is a bitmask and the following bits can be set:
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0x01: Log the ioctl name and error code. VIDIOC_(D)QBUF ioctls are only logged
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if bit 0x08 is also set.
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0x02: Log the ioctl name arguments and error code. VIDIOC_(D)QBUF ioctls are
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only logged if bit 0x08 is also set.
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0x04: Log the file operations open, release, read, write, mmap and
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get_unmapped_area. The read and write operations are only logged if
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bit 0x08 is also set.
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0x08: Log the read and write file operations and the VIDIOC_QBUF and
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VIDIOC_DQBUF ioctls.
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0x10: Log the poll file operation.
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.. code-block:: none
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0x01: Log the ioctl name and error code. VIDIOC_(D)QBUF ioctls are only logged
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if bit 0x08 is also set.
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0x02: Log the ioctl name arguments and error code. VIDIOC_(D)QBUF ioctls are
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only logged if bit 0x08 is also set.
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0x04: Log the file operations open, release, read, write, mmap and
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get_unmapped_area. The read and write operations are only logged if
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bit 0x08 is also set.
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0x08: Log the read and write file operations and the VIDIOC_QBUF and
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VIDIOC_DQBUF ioctls.
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0x10: Log the poll file operation.
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video_device cleanup
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--------------------
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@ -845,6 +907,8 @@ 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:
|
||||
|
||||
.. code-block:: none
|
||||
|
||||
video_unregister_device(vdev);
|
||||
|
||||
This will remove the device nodes from sysfs (causing udev to remove them
|
||||
|
|
@ -861,6 +925,8 @@ 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:
|
||||
|
||||
.. code-block:: none
|
||||
|
||||
media_entity_cleanup(&vdev->entity);
|
||||
|
||||
This can be done from the release callback.
|
||||
|
|
@ -875,31 +941,41 @@ There are a few useful helper functions:
|
|||
|
||||
You can set/get driver private data in the video_device struct using:
|
||||
|
||||
void *video_get_drvdata(struct video_device *vdev);
|
||||
void video_set_drvdata(struct video_device *vdev, void *data);
|
||||
.. code-block:: none
|
||||
|
||||
void *video_get_drvdata(struct video_device *vdev);
|
||||
void video_set_drvdata(struct video_device *vdev, void *data);
|
||||
|
||||
Note that you can safely call video_set_drvdata() before calling
|
||||
video_register_device().
|
||||
|
||||
And this function:
|
||||
|
||||
struct video_device *video_devdata(struct file *file);
|
||||
.. code-block:: none
|
||||
|
||||
struct video_device *video_devdata(struct file *file);
|
||||
|
||||
returns the video_device belonging to the file struct.
|
||||
|
||||
The video_drvdata function combines video_get_drvdata with video_devdata:
|
||||
|
||||
void *video_drvdata(struct file *file);
|
||||
.. code-block:: none
|
||||
|
||||
void *video_drvdata(struct file *file);
|
||||
|
||||
You can go from a video_device struct to the v4l2_device struct using:
|
||||
|
||||
struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
|
||||
.. code-block:: none
|
||||
|
||||
struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
|
||||
|
||||
- Device node name
|
||||
|
||||
The video_device node kernel name can be retrieved using
|
||||
|
||||
const char *video_device_node_name(struct video_device *vdev);
|
||||
.. code-block:: none
|
||||
|
||||
const char *video_device_node_name(struct video_device *vdev);
|
||||
|
||||
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
|
||||
|
|
@ -943,64 +1019,74 @@ v4l2_fh_del+v4l2_fh_exit in release().
|
|||
Drivers can extract their own file handle structure by using the container_of
|
||||
macro. Example:
|
||||
|
||||
struct my_fh {
|
||||
int blah;
|
||||
struct v4l2_fh fh;
|
||||
};
|
||||
.. code-block:: none
|
||||
|
||||
...
|
||||
|
||||
int my_open(struct file *file)
|
||||
{
|
||||
struct my_fh *my_fh;
|
||||
struct video_device *vfd;
|
||||
int ret;
|
||||
struct my_fh {
|
||||
int blah;
|
||||
struct v4l2_fh fh;
|
||||
};
|
||||
|
||||
...
|
||||
|
||||
my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL);
|
||||
int my_open(struct file *file)
|
||||
{
|
||||
struct my_fh *my_fh;
|
||||
struct video_device *vfd;
|
||||
int ret;
|
||||
|
||||
...
|
||||
...
|
||||
|
||||
v4l2_fh_init(&my_fh->fh, vfd);
|
||||
my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL);
|
||||
|
||||
...
|
||||
...
|
||||
|
||||
file->private_data = &my_fh->fh;
|
||||
v4l2_fh_add(&my_fh->fh);
|
||||
return 0;
|
||||
}
|
||||
v4l2_fh_init(&my_fh->fh, vfd);
|
||||
|
||||
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;
|
||||
}
|
||||
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:
|
||||
|
||||
void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev)
|
||||
.. 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.
|
||||
|
||||
void v4l2_fh_add(struct v4l2_fh *fh)
|
||||
.. 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.
|
||||
|
||||
void v4l2_fh_del(struct v4l2_fh *fh)
|
||||
.. 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.
|
||||
|
||||
void v4l2_fh_exit(struct v4l2_fh *fh)
|
||||
.. code-block:: none
|
||||
|
||||
void v4l2_fh_exit(struct v4l2_fh *fh)
|
||||
|
||||
Uninitialise the file handle. After uninitialisation the v4l2_fh
|
||||
memory can be freed.
|
||||
|
|
@ -1008,12 +1094,16 @@ void v4l2_fh_exit(struct v4l2_fh *fh)
|
|||
|
||||
If struct v4l2_fh is not embedded, then you can use these helper functions:
|
||||
|
||||
int v4l2_fh_open(struct file *filp)
|
||||
.. 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.
|
||||
|
||||
int v4l2_fh_release(struct file *filp)
|
||||
.. 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.
|
||||
|
|
@ -1027,11 +1117,15 @@ 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:
|
||||
|
||||
int v4l2_fh_is_singular(struct v4l2_fh *fh)
|
||||
.. 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.
|
||||
|
||||
int v4l2_fh_is_singular_file(struct file *filp)
|
||||
.. code-block:: none
|
||||
|
||||
int v4l2_fh_is_singular_file(struct file *filp)
|
||||
|
||||
Same, but it calls v4l2_fh_is_singular with filp->private_data.
|
||||
|
||||
|
|
@ -1075,15 +1169,19 @@ fast.
|
|||
|
||||
Useful functions:
|
||||
|
||||
void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev)
|
||||
.. code-block:: none
|
||||
|
||||
void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev)
|
||||
|
||||
Queue events to video device. The driver's only responsibility is to fill
|
||||
in the type and the data fields. The other fields will be filled in by
|
||||
V4L2.
|
||||
|
||||
int v4l2_event_subscribe(struct v4l2_fh *fh,
|
||||
struct v4l2_event_subscription *sub, unsigned elems,
|
||||
const struct v4l2_subscribed_event_ops *ops)
|
||||
.. code-block:: none
|
||||
|
||||
int v4l2_event_subscribe(struct v4l2_fh *fh,
|
||||
struct v4l2_event_subscription *sub, unsigned elems,
|
||||
const struct v4l2_subscribed_event_ops *ops)
|
||||
|
||||
The video_device->ioctl_ops->vidioc_subscribe_event must check the driver
|
||||
is able to produce events with specified event id. Then it calls
|
||||
|
|
@ -1102,8 +1200,10 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
|
|||
All 4 callbacks are optional, if you don't want to specify any callbacks
|
||||
the ops argument itself maybe NULL.
|
||||
|
||||
int v4l2_event_unsubscribe(struct v4l2_fh *fh,
|
||||
struct v4l2_event_subscription *sub)
|
||||
.. code-block:: none
|
||||
|
||||
int v4l2_event_unsubscribe(struct v4l2_fh *fh,
|
||||
struct v4l2_event_subscription *sub)
|
||||
|
||||
vidioc_unsubscribe_event in struct v4l2_ioctl_ops. A driver may use
|
||||
v4l2_event_unsubscribe() directly unless it wants to be involved in
|
||||
|
|
@ -1112,7 +1212,9 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
|
|||
The special type V4L2_EVENT_ALL may be used to unsubscribe all events. The
|
||||
drivers may want to handle this in a special way.
|
||||
|
||||
int v4l2_event_pending(struct v4l2_fh *fh)
|
||||
.. code-block:: none
|
||||
|
||||
int v4l2_event_pending(struct v4l2_fh *fh)
|
||||
|
||||
Returns the number of pending events. Useful when implementing poll.
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue