Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.
1 What callbacks will usbcore do? 2 =============================== 3 4 Usbcore will call into a driver through callbacks defined in the driver 5 structure and through the completion handler of URBs a driver submits. 6 Only the former are in the scope of this document. These two kinds of 7 callbacks are completely independent of each other. Information on the 8 completion callback can be found in Documentation/usb/URB.txt. 9 10 The callbacks defined in the driver structure are: 11 12 1. Hotplugging callbacks: 13 14 * @probe: Called to see if the driver is willing to manage a particular 15 * interface on a device. 16 * @disconnect: Called when the interface is no longer accessible, usually 17 * because its device has been (or is being) disconnected or the 18 * driver module is being unloaded. 19 20 2. Odd backdoor through usbfs: 21 22 * @ioctl: Used for drivers that want to talk to userspace through 23 * the "usbfs" filesystem. This lets devices provide ways to 24 * expose information to user space regardless of where they 25 * do (or don't) show up otherwise in the filesystem. 26 27 3. Power management (PM) callbacks: 28 29 * @suspend: Called when the device is going to be suspended. 30 * @resume: Called when the device is being resumed. 31 * @reset_resume: Called when the suspended device has been reset instead 32 * of being resumed. 33 34 4. Device level operations: 35 36 * @pre_reset: Called when the device is about to be reset. 37 * @post_reset: Called after the device has been reset 38 39 The ioctl interface (2) should be used only if you have a very good 40 reason. Sysfs is preferred these days. The PM callbacks are covered 41 separately in Documentation/usb/power-management.txt. 42 43 Calling conventions 44 =================== 45 46 All callbacks are mutually exclusive. There's no need for locking 47 against other USB callbacks. All callbacks are called from a task 48 context. You may sleep. However, it is important that all sleeps have a 49 small fixed upper limit in time. In particular you must not call out to 50 user space and await results. 51 52 Hotplugging callbacks 53 ===================== 54 55 These callbacks are intended to associate and disassociate a driver with 56 an interface. A driver's bond to an interface is exclusive. 57 58 The probe() callback 59 -------------------- 60 61 int (*probe) (struct usb_interface *intf, 62 const struct usb_device_id *id); 63 64 Accept or decline an interface. If you accept the device return 0, 65 otherwise -ENODEV or -ENXIO. Other error codes should be used only if a 66 genuine error occurred during initialisation which prevented a driver 67 from accepting a device that would else have been accepted. 68 You are strongly encouraged to use usbcore's facility, 69 usb_set_intfdata(), to associate a data structure with an interface, so 70 that you know which internal state and identity you associate with a 71 particular interface. The device will not be suspended and you may do IO 72 to the interface you are called for and endpoint 0 of the device. Device 73 initialisation that doesn't take too long is a good idea here. 74 75 The disconnect() callback 76 ------------------------- 77 78 void (*disconnect) (struct usb_interface *intf); 79 80 This callback is a signal to break any connection with an interface. 81 You are not allowed any IO to a device after returning from this 82 callback. You also may not do any other operation that may interfere 83 with another driver bound the interface, eg. a power management 84 operation. 85 If you are called due to a physical disconnection, all your URBs will be 86 killed by usbcore. Note that in this case disconnect will be called some 87 time after the physical disconnection. Thus your driver must be prepared 88 to deal with failing IO even prior to the callback. 89 90 Device level callbacks 91 ====================== 92 93 pre_reset 94 --------- 95 96 int (*pre_reset)(struct usb_interface *intf); 97 98 A driver or user space is triggering a reset on the device which 99 contains the interface passed as an argument. Cease IO, wait for all 100 outstanding URBs to complete, and save any device state you need to 101 restore. No more URBs may be submitted until the post_reset method 102 is called. 103 104 If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you 105 are in atomic context. 106 107 post_reset 108 ---------- 109 110 int (*post_reset)(struct usb_interface *intf); 111 112 The reset has completed. Restore any saved device state and begin 113 using the device again. 114 115 If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you 116 are in atomic context. 117 118 Call sequences 119 ============== 120 121 No callbacks other than probe will be invoked for an interface 122 that isn't bound to your driver. 123 124 Probe will never be called for an interface bound to a driver. 125 Hence following a successful probe, disconnect will be called 126 before there is another probe for the same interface. 127 128 Once your driver is bound to an interface, disconnect can be 129 called at any time except in between pre_reset and post_reset. 130 pre_reset is always followed by post_reset, even if the reset 131 failed or the device has been unplugged. 132 133 suspend is always followed by one of: resume, reset_resume, or 134 disconnect.