1  <title>V4L2 Driver Programming</title>
2
3  <!-- This part defines the interface between the "videodev"
4    module and individual drivers. -->
5
6  <para>to do</para>
7<!--
8  <para>V4L2 is a two-layer driver system. The top layer is the "videodev"
9kernel module. When videodev initializes it registers as character device
10with major number 81, and it registers a set of file operations. All V4L2
11drivers are really clients of videodev, which calls V4L2 drivers through
12driver method functions. V4L2 drivers are also written as kernel modules.
13After probing the hardware they register one or more devices with
14videodev.</para>
15
16  <section id="driver-modules">
17    <title>Driver Modules</title>
18
19    <para>V4L2 driver modules must have an initialization function which is
20called after the module was loaded into kernel, an exit function whis is
21called before the module is removed.  When the driver is compiled into the
22kernel these functions called at system boot and shutdown time.</para>
23
24    <informalexample>
25      <programlisting>
26#include &lt;linux/module.h&gt;
27
28/* Export information about this module. For details and other useful
29   macros see <filename>linux/module.h</filename>. */
30MODULE_DESCRIPTION("my - driver for my hardware");
31MODULE_AUTHOR("Your name here");
32MODULE_LICENSE("GPL");
33
34static void
35my_module_exit (void)
36{
37	/* Free all resources allocated by my_module_init(). */
38}
39
40static int
41my_module_init (void)
42{
43	/* Bind the driver to the supported hardware, see
44	   <link linkend="driver-pci"> and
45	   <link linkend="driver-usb"> for examples. */
46
47	return 0; /* a negative value on error, 0 on success. */
48}
49
50/* Export module functions. */
51module_init (my_module_init);
52module_exit (my_module_exit);
53</programlisting>
54    </informalexample>
55
56    <para>Users can add parameters when kernel modules are inserted:</para>
57
58    <informalexample>
59      <programlisting>
60include &lt;linux/moduleparam.h&gt;
61
62static int my_option = 123;
63static int my_option_array[47];
64
65/* Export the symbol, an int, with access permissions 0664.
66   See <filename>linux/moduleparam.h</filename> for other types. */
67module_param (my_option, int, 0644);
68module_param_array (my_option_array, int, NULL, 0644);
69
70MODULE_PARM_DESC (my_option, "Does magic things, default 123");
71</programlisting>
72    </informalexample>
73
74    <para>One parameter should be supported by all V4L2 drivers, the minor
75number of the device it will register. Purpose is to predictably link V4L2
76drivers to device nodes if more than one video device is installed. Use the
77name of the device node followed by a "_nr" suffix, for example "video_nr"
78for <filename>/dev/video</filename>.</para>
79
80    <informalexample>
81      <programlisting>
82/* Minor number of the device, -1 to allocate the first unused. */
83static int video_nr = -1;
84
85module_param (video_nr, int, 0444);
86</programlisting>
87    </informalexample>
88  </section>
89
90  <section id="driver-pci">
91    <title>PCI Devices</title>
92
93    <para>PCI devices are initialized like this:</para>
94
95    <informalexample>
96      <programlisting>
97typedef struct {
98	/* State of one physical device. */
99} my_device;
100
101static int
102my_resume               (struct pci_dev *               pci_dev)
103{
104	/* Restore the suspended device to working state. */
105}
106
107static int
108my_suspend              (struct pci_dev *               pci_dev,
109			 pm_message_t                   state)
110{
111	/* This function is called before the system goes to sleep.
112	   Stop all DMAs and disable interrupts, then put the device
113	   into a low power state. For details see the kernel
114	   sources under <filename>Documentation/power</filename>. */
115
116	return 0; /* a negative value on error, 0 on success. */
117}
118
119static void
120my_remove               (struct pci_dev *               pci_dev)
121{
122	my_device *my = pci_get_drvdata (pci_dev);
123
124	/* Describe me. */
125}
126
127static int
128my_probe                (struct pci_dev *               pci_dev,
129			 const struct pci_device_id *   pci_id)
130{
131	my_device *my;
132
133	/* Describe me. */
134
135	/* You can allocate per-device data here and store a pointer
136	   to it in the pci_dev structure. */
137	my = ...;
138	pci_set_drvdata (pci_dev, my);
139
140	return 0; /* a negative value on error, 0 on success. */
141}
142
143/* A list of supported PCI devices. */
144static struct pci_device_id
145my_pci_device_ids [] = {
146	{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
147	  PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 },
148	{ 0 } /* end of list */
149};
150
151/* Load our module if supported PCI devices are installed. */
152MODULE_DEVICE_TABLE (pci, my_pci_device_ids);
153
154static struct pci_driver
155my_pci_driver = {
156	.name     = "my",
157	.id_table = my_pci_device_ids,
158
159	.probe    = my_probe,
160	.remove   = my_remove,
161
162	/* Power management functions. */
163	.suspend  = my_suspend,
164	.resume   = my_resume,
165};
166
167static void
168my_module_exit          (void)
169{
170	pci_unregister_driver (&my_pci_driver);
171}
172
173static int
174my_module_init          (void)
175{
176	return pci_register_driver (&my_pci_driver);
177}
178</programlisting>
179    </informalexample>
180  </section>
181
182  <section id="driver-usb">
183    <title>USB Devices</title>
184    <para>to do</para>
185  </section>
186  <section id="driver-registering">
187    <title>Registering V4L2 Drivers</title>
188
189    <para>After a V4L2 driver probed the hardware it registers one or more
190devices with the videodev module.</para>
191  </section>
192  <section id="driver-file-ops">
193    <title>File Operations</title>
194    <para>to do</para>
195  </section>
196  <section id="driver-internal-api">
197    <title>Internal API</title>
198    <para>to do</para>
199  </section>
200-->
201