![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
The V4L and DVB API's are there for a long time. however, up to now, no efforts were done to merge them to kernel DocBook. This patch adds the current versions of the specs as an unique compendium. Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
209 lines
5.5 KiB
XML
209 lines
5.5 KiB
XML
<title>V4L2 Driver Programming</title>
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<!-- This part defines the interface between the "videodev"
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module and individual drivers. -->
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<para>to do</para>
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<!--
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<para>V4L2 is a two-layer driver system. The top layer is the "videodev"
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kernel module. When videodev initializes it registers as character device
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with major number 81, and it registers a set of file operations. All V4L2
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drivers are really clients of videodev, which calls V4L2 drivers through
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driver method functions. V4L2 drivers are also written as kernel modules.
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After probing the hardware they register one or more devices with
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videodev.</para>
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<section id="driver-modules">
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<title>Driver Modules</title>
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<para>V4L2 driver modules must have an initialization function which is
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called after the module was loaded into kernel, an exit function whis is
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called before the module is removed. When the driver is compiled into the
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kernel these functions called at system boot and shutdown time.</para>
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<informalexample>
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<programlisting>
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#include <linux/module.h>
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/* Export information about this module. For details and other useful
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macros see <filename>linux/module.h</filename>. */
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MODULE_DESCRIPTION("my - driver for my hardware");
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MODULE_AUTHOR("Your name here");
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MODULE_LICENSE("GPL");
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static void
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my_module_exit (void)
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{
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/* Free all resources allocated by my_module_init(). */
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}
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static int
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my_module_init (void)
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{
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/* Bind the driver to the supported hardware, see
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<link linkend="driver-pci"> and
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<link linkend="driver-usb"> for examples. */
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return 0; /* a negative value on error, 0 on success. */
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}
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/* Export module functions. */
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module_init (my_module_init);
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module_exit (my_module_exit);
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</programlisting>
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</informalexample>
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<para>Users can add parameters when kernel modules are inserted:</para>
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<informalexample>
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<programlisting>
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include <linux/moduleparam.h>
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static int my_option = 123;
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static int my_option_array[47];
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/* Export the symbol, an int, with access permissions 0664.
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See <filename>linux/moduleparam.h</filename> for other types. */
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module_param (my_option, int, 0644);
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module_param_array (my_option_array, int, NULL, 0644);
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MODULE_PARM_DESC (my_option, "Does magic things, default 123");
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</programlisting>
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</informalexample>
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<para>One parameter should be supported by all V4L2 drivers, the minor
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number of the device it will register. Purpose is to predictably link V4L2
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drivers to device nodes if more than one video device is installed. Use the
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name of the device node followed by a "_nr" suffix, for example "video_nr"
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for <filename>/dev/video</filename>.</para>
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<informalexample>
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<programlisting>
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/* Minor number of the device, -1 to allocate the first unused. */
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static int video_nr = -1;
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module_param (video_nr, int, 0444);
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</programlisting>
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</informalexample>
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</section>
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<section id="driver-pci">
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<title>PCI Devices</title>
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<para>PCI devices are initialized like this:</para>
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<informalexample>
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<programlisting>
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typedef struct {
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/* State of one physical device. */
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} my_device;
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static int
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my_resume (struct pci_dev * pci_dev)
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{
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/* Restore the suspended device to working state. */
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}
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static int
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my_suspend (struct pci_dev * pci_dev,
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pm_message_t state)
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{
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/* This function is called before the system goes to sleep.
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Stop all DMAs and disable interrupts, then put the device
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into a low power state. For details see the kernel
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sources under <filename>Documentation/power</filename>. */
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return 0; /* a negative value on error, 0 on success. */
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}
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static void __devexit
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my_remove (struct pci_dev * pci_dev)
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{
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my_device *my = pci_get_drvdata (pci_dev);
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/* Describe me. */
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}
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static int __devinit
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my_probe (struct pci_dev * pci_dev,
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const struct pci_device_id * pci_id)
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{
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my_device *my;
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/* Describe me. */
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/* You can allocate per-device data here and store a pointer
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to it in the pci_dev structure. */
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my = ...;
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pci_set_drvdata (pci_dev, my);
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return 0; /* a negative value on error, 0 on success. */
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}
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/* A list of supported PCI devices. */
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static struct pci_device_id
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my_pci_device_ids [] = {
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{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
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PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 },
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{ 0 } /* end of list */
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};
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/* Load our module if supported PCI devices are installed. */
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MODULE_DEVICE_TABLE (pci, my_pci_device_ids);
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static struct pci_driver
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my_pci_driver = {
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.name = "my",
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.id_table = my_pci_device_ids,
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.probe = my_probe,
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.remove = __devexit_p (my_remove),
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/* Power management functions. */
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.suspend = my_suspend,
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.resume = my_resume,
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};
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static void
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my_module_exit (void)
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{
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pci_unregister_driver (&my_pci_driver);
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}
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static int
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my_module_init (void)
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{
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return pci_register_driver (&my_pci_driver);
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}
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</programlisting>
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</informalexample>
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</section>
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<section id="driver-usb">
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<title>USB Devices</title>
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<para>to do</para>
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</section>
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<section id="driver-registering">
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<title>Registering V4L2 Drivers</title>
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<para>After a V4L2 driver probed the hardware it registers one or more
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devices with the videodev module.</para>
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</section>
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<section id="driver-file-ops">
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<title>File Operations</title>
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<para>to do</para>
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</section>
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<section id="driver-internal-api">
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<title>Internal API</title>
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<para>to do</para>
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</section>
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-->
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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