diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/driver.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/driver.xml | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/Documentation/DocBook/media/v4l/driver.xml b/Documentation/DocBook/media/v4l/driver.xml new file mode 100644 index 000000000..7c6638bac --- /dev/null +++ b/Documentation/DocBook/media/v4l/driver.xml @@ -0,0 +1,200 @@ + <title>V4L2 Driver Programming</title> + + <!-- This part defines the interface between the "videodev" + module and individual drivers. --> + + <para>to do</para> +<!-- + <para>V4L2 is a two-layer driver system. The top layer is the "videodev" +kernel module. When videodev initializes it registers as character device +with major number 81, and it registers a set of file operations. All V4L2 +drivers are really clients of videodev, which calls V4L2 drivers through +driver method functions. V4L2 drivers are also written as kernel modules. +After probing the hardware they register one or more devices with +videodev.</para> + + <section id="driver-modules"> + <title>Driver Modules</title> + + <para>V4L2 driver modules must have an initialization function which is +called after the module was loaded into kernel, an exit function whis is +called before the module is removed. When the driver is compiled into the +kernel these functions called at system boot and shutdown time.</para> + + <informalexample> + <programlisting> +#include <linux/module.h> + +/* Export information about this module. For details and other useful + macros see <filename>linux/module.h</filename>. */ +MODULE_DESCRIPTION("my - driver for my hardware"); +MODULE_AUTHOR("Your name here"); +MODULE_LICENSE("GPL"); + +static void +my_module_exit (void) +{ + /* Free all resources allocated by my_module_init(). */ +} + +static int +my_module_init (void) +{ + /* Bind the driver to the supported hardware, see + <link linkend="driver-pci"> and + <link linkend="driver-usb"> for examples. */ + + return 0; /* a negative value on error, 0 on success. */ +} + +/* Export module functions. */ +module_init (my_module_init); +module_exit (my_module_exit); +</programlisting> + </informalexample> + + <para>Users can add parameters when kernel modules are inserted:</para> + + <informalexample> + <programlisting> +include <linux/moduleparam.h> + +static int my_option = 123; +static int my_option_array[47]; + +/* Export the symbol, an int, with access permissions 0664. + See <filename>linux/moduleparam.h</filename> for other types. */ +module_param (my_option, int, 0644); +module_param_array (my_option_array, int, NULL, 0644); + +MODULE_PARM_DESC (my_option, "Does magic things, default 123"); +</programlisting> + </informalexample> + + <para>One parameter should be supported by all V4L2 drivers, the minor +number of the device it will register. Purpose is to predictably link V4L2 +drivers to device nodes if more than one video device is installed. Use the +name of the device node followed by a "_nr" suffix, for example "video_nr" +for <filename>/dev/video</filename>.</para> + + <informalexample> + <programlisting> +/* Minor number of the device, -1 to allocate the first unused. */ +static int video_nr = -1; + +module_param (video_nr, int, 0444); +</programlisting> + </informalexample> + </section> + + <section id="driver-pci"> + <title>PCI Devices</title> + + <para>PCI devices are initialized like this:</para> + + <informalexample> + <programlisting> +typedef struct { + /* State of one physical device. */ +} my_device; + +static int +my_resume (struct pci_dev * pci_dev) +{ + /* Restore the suspended device to working state. */ +} + +static int +my_suspend (struct pci_dev * pci_dev, + pm_message_t state) +{ + /* This function is called before the system goes to sleep. + Stop all DMAs and disable interrupts, then put the device + into a low power state. For details see the kernel + sources under <filename>Documentation/power</filename>. */ + + return 0; /* a negative value on error, 0 on success. */ +} + +static void +my_remove (struct pci_dev * pci_dev) +{ + my_device *my = pci_get_drvdata (pci_dev); + + /* Describe me. */ +} + +static int +my_probe (struct pci_dev * pci_dev, + const struct pci_device_id * pci_id) +{ + my_device *my; + + /* Describe me. */ + + /* You can allocate per-device data here and store a pointer + to it in the pci_dev structure. */ + my = ...; + pci_set_drvdata (pci_dev, my); + + return 0; /* a negative value on error, 0 on success. */ +} + +/* A list of supported PCI devices. */ +static struct pci_device_id +my_pci_device_ids [] = { + { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, + PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 }, + { 0 } /* end of list */ +}; + +/* Load our module if supported PCI devices are installed. */ +MODULE_DEVICE_TABLE (pci, my_pci_device_ids); + +static struct pci_driver +my_pci_driver = { + .name = "my", + .id_table = my_pci_device_ids, + + .probe = my_probe, + .remove = my_remove, + + /* Power management functions. */ + .suspend = my_suspend, + .resume = my_resume, +}; + +static void +my_module_exit (void) +{ + pci_unregister_driver (&my_pci_driver); +} + +static int +my_module_init (void) +{ + return pci_register_driver (&my_pci_driver); +} +</programlisting> + </informalexample> + </section> + + <section id="driver-usb"> + <title>USB Devices</title> + <para>to do</para> + </section> + <section id="driver-registering"> + <title>Registering V4L2 Drivers</title> + + <para>After a V4L2 driver probed the hardware it registers one or more +devices with the videodev module.</para> + </section> + <section id="driver-file-ops"> + <title>File Operations</title> + <para>to do</para> + </section> + <section id="driver-internal-api"> + <title>Internal API</title> + <para>to do</para> + </section> +--> |