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Diffstat (limited to 'Documentation/usb')
| -rw-r--r-- | Documentation/usb/hotplug.txt | 148 |
1 files changed, 0 insertions, 148 deletions
diff --git a/Documentation/usb/hotplug.txt b/Documentation/usb/hotplug.txt deleted file mode 100644 index 5b243f315b2c..000000000000 --- a/Documentation/usb/hotplug.txt +++ /dev/null @@ -1,148 +0,0 @@ -LINUX HOTPLUGGING - -In hotpluggable busses like USB (and Cardbus PCI), end-users plug devices -into the bus with power on. In most cases, users expect the devices to become -immediately usable. That means the system must do many things, including: - - - Find a driver that can handle the device. That may involve - loading a kernel module; newer drivers can use module-init-tools - to publish their device (and class) support to user utilities. - - - Bind a driver to that device. Bus frameworks do that using a - device driver's probe() routine. - - - Tell other subsystems to configure the new device. Print - queues may need to be enabled, networks brought up, disk - partitions mounted, and so on. In some cases these will - be driver-specific actions. - -This involves a mix of kernel mode and user mode actions. Making devices -be immediately usable means that any user mode actions can't wait for an -administrator to do them: the kernel must trigger them, either passively -(triggering some monitoring daemon to invoke a helper program) or -actively (calling such a user mode helper program directly). - -Those triggered actions must support a system's administrative policies; -such programs are called "policy agents" here. Typically they involve -shell scripts that dispatch to more familiar administration tools. - -Because some of those actions rely on information about drivers (metadata) -that is currently available only when the drivers are dynamically linked, -you get the best hotplugging when you configure a highly modular system. - - -KERNEL HOTPLUG HELPER (/sbin/hotplug) - -There is a kernel parameter: /proc/sys/kernel/hotplug, which normally -holds the pathname "/sbin/hotplug". That parameter names a program -which the kernel may invoke at various times. - -The /sbin/hotplug program can be invoked by any subsystem as part of its -reaction to a configuration change, from a thread in that subsystem. -Only one parameter is required: the name of a subsystem being notified of -some kernel event. That name is used as the first key for further event -dispatch; any other argument and environment parameters are specified by -the subsystem making that invocation. - -Hotplug software and other resources is available at: - - http://linux-hotplug.sourceforge.net - -Mailing list information is also available at that site. - - --------------------------------------------------------------------------- - - -USB POLICY AGENT - -The USB subsystem currently invokes /sbin/hotplug when USB devices -are added or removed from system. The invocation is done by the kernel -hub workqueue [hub_wq], or else as part of root hub initialization -(done by init, modprobe, kapmd, etc). Its single command line parameter -is the string "usb", and it passes these environment variables: - - ACTION ... "add", "remove" - PRODUCT ... USB vendor, product, and version codes (hex) - TYPE ... device class codes (decimal) - INTERFACE ... interface 0 class codes (decimal) - -If "usbdevfs" is configured, DEVICE and DEVFS are also passed. DEVICE is -the pathname of the device, and is useful for devices with multiple and/or -alternate interfaces that complicate driver selection. By design, USB -hotplugging is independent of "usbdevfs": you can do most essential parts -of USB device setup without using that filesystem, and without running a -user mode daemon to detect changes in system configuration. - -Currently available policy agent implementations can load drivers for -modules, and can invoke driver-specific setup scripts. The newest ones -leverage USB module-init-tools support. Later agents might unload drivers. - - -USB MODUTILS SUPPORT - -Current versions of module-init-tools will create a "modules.usbmap" file -which contains the entries from each driver's MODULE_DEVICE_TABLE. Such -files can be used by various user mode policy agents to make sure all the -right driver modules get loaded, either at boot time or later. - -See <linux/usb.h> for full information about such table entries; or look -at existing drivers. Each table entry describes one or more criteria to -be used when matching a driver to a device or class of devices. The -specific criteria are identified by bits set in "match_flags", paired -with field values. You can construct the criteria directly, or with -macros such as these, and use driver_info to store more information. - - USB_DEVICE (vendorId, productId) - ... matching devices with specified vendor and product ids - USB_DEVICE_VER (vendorId, productId, lo, hi) - ... like USB_DEVICE with lo <= productversion <= hi - USB_INTERFACE_INFO (class, subclass, protocol) - ... matching specified interface class info - USB_DEVICE_INFO (class, subclass, protocol) - ... matching specified device class info - -A short example, for a driver that supports several specific USB devices -and their quirks, might have a MODULE_DEVICE_TABLE like this: - - static const struct usb_device_id mydriver_id_table[] = { - { USB_DEVICE (0x9999, 0xaaaa), driver_info: QUIRK_X }, - { USB_DEVICE (0xbbbb, 0x8888), driver_info: QUIRK_Y|QUIRK_Z }, - ... - { } /* end with an all-zeroes entry */ - }; - MODULE_DEVICE_TABLE(usb, mydriver_id_table); - -Most USB device drivers should pass these tables to the USB subsystem as -well as to the module management subsystem. Not all, though: some driver -frameworks connect using interfaces layered over USB, and so they won't -need such a "struct usb_driver". - -Drivers that connect directly to the USB subsystem should be declared -something like this: - - static struct usb_driver mydriver = { - .name = "mydriver", - .id_table = mydriver_id_table, - .probe = my_probe, - .disconnect = my_disconnect, - - /* - if using the usb chardev framework: - .minor = MY_USB_MINOR_START, - .fops = my_file_ops, - if exposing any operations through usbdevfs: - .ioctl = my_ioctl, - */ - }; - -When the USB subsystem knows about a driver's device ID table, it's used when -choosing drivers to probe(). The thread doing new device processing checks -drivers' device ID entries from the MODULE_DEVICE_TABLE against interface and -device descriptors for the device. It will only call probe() if there is a -match, and the third argument to probe() will be the entry that matched. - -If you don't provide an id_table for your driver, then your driver may get -probed for each new device; the third parameter to probe() will be null. - - |