Based on kernel version 4.10.8. Page generated on 2017-04-01 14:43 EST.
1 2 Staging/Android Switch Class Porting Guide 3 (linux/drivers/staging/android/switch) 4 (c) Copyright 2012 Samsung Electronics 5 6 AUTHORS 7 MyungJoo Ham <myungjoo.ham@samsung.com> 8 9 /***************************************************************** 10 * CHAPTER 1. * 11 * PORTING SWITCH CLASS DEVICE DRIVERS * 12 *****************************************************************/ 13 14 ****** STEP 1. Basic Functionality 15 No extcon extended feature, but switch features only. 16 17 - struct switch_dev (fed to switch_dev_register/unregister) 18 @name: no change 19 @dev: no change 20 @index: drop (not used in switch device driver side anyway) 21 @state: no change 22 If you have used @state with magic numbers, keep it 23 at this step. 24 @print_name: no change but type change (switch_dev->extcon_dev) 25 @print_state: no change but type change (switch_dev->extcon_dev) 26 27 - switch_dev_register(sdev, dev) 28 => extcon_dev_register(edev) 29 : type change (sdev->edev) 30 : remove second param('dev'). if edev has parent device, should store 31 'dev' to 'edev.dev.parent' before registering extcon device 32 - switch_dev_unregister(sdev) 33 => extcon_dev_unregister(edev) 34 : no change but type change (sdev->edev) 35 - switch_get_state(sdev) 36 => extcon_get_state(edev) 37 : no change but type change (sdev->edev) and (return: int->u32) 38 - switch_set_state(sdev, state) 39 => extcon_set_state(edev, state) 40 : no change but type change (sdev->edev) and (state: int->u32) 41 42 With this changes, the ex-switch extcon class device works as it once 43 worked as switch class device. However, it will now have additional 44 interfaces (both ABI and in-kernel API) and different ABI locations. 45 However, if CONFIG_ANDROID is enabled without CONFIG_ANDROID_SWITCH, 46 /sys/class/switch/* will be symbolically linked to /sys/class/extcon/ 47 so that they are still compatible with legacy userspace processes. 48 49 ****** STEP 2. Multistate (no more magic numbers in state value) 50 Extcon's extended features for switch device drivers with 51 complex features usually required magic numbers in state 52 value of switch_dev. With extcon, such magic numbers that 53 support multiple cables are no more required or supported. 54 55 1. Define cable names at edev->supported_cable. 56 2. (Recommended) remove print_state callback. 57 3. Use extcon_get_cable_state_(edev, index) or 58 extcon_get_cable_state(edev, cable_name) instead of 59 extcon_get_state(edev) if you intend to get a state of a specific 60 cable. Same for set_state. This way, you can remove the usage of 61 magic numbers in state value. 62 4. Use extcon_update_state() if you are updating specific bits of 63 the state value. 64 65 Example: a switch device driver w/ magic numbers for two cables. 66 "0x00": no cables connected. 67 "0x01": cable 1 connected 68 "0x02": cable 2 connected 69 "0x03": cable 1 and 2 connected 70 1. edev->supported_cable = {"1", "2", NULL}; 71 2. edev->print_state = NULL; 72 3. extcon_get_cable_state_(edev, 0) shows cable 1's state. 73 extcon_get_cable_state(edev, "1") shows cable 1's state. 74 extcon_set_cable_state_(edev, 1) sets cable 2's state. 75 extcon_set_cable_state(edev, "2") sets cable 2's state 76 4. extcon_update_state(edev, 0x01, 0) sets the least bit's 0. 77 78 ****** STEP 3. Notify other device drivers 79 80 You can notify others of the cable attach/detach events with 81 notifier chains. 82 83 At the side of other device drivers (the extcon device itself 84 does not need to get notified of its own events), there are two 85 methods to register notifier_block for cable events: 86 (a) for a specific cable or (b) for every cable. 87 88 (a) extcon_register_interest(obj, extcon_name, cable_name, nb) 89 Example: want to get news of "MAX8997_MUIC"'s "USB" cable 90 91 obj = kzalloc(sizeof(struct extcon_specific_cable_nb), 92 GFP_KERNEL); 93 nb->notifier_call = the_callback_to_handle_usb; 94 95 extcon_register_intereset(obj, "MAX8997_MUIC", "USB", nb); 96 97 (b) extcon_register_notifier(edev, nb) 98 Call nb for any changes in edev. 99 100 Please note that in order to properly behave with method (a), 101 the extcon device driver should support multistate feature (STEP 2). 102 103 ****** STEP 4. Inter-cable relation (mutually exclusive) 104 105 You can provide inter-cable mutually exclusiveness information 106 for an extcon device. When cables A and B are declared to be mutually 107 exclusive, the two cables cannot be in ATTACHED state simulteneously. 108 109 110 /***************************************************************** 111 * CHAPTER 2. * 112 * PORTING USERSPACE w/ SWITCH CLASS DEVICE SUPPORT * 113 *****************************************************************/ 114 115 ****** ABI Location 116 117 If "CONFIG_ANDROID" is enabled, /sys/class/switch/* are created 118 as symbolic links to /sys/class/extcon/*. 119 120 The two files of switch class, name and state, are provided with 121 extcon, too. When the multistate support (STEP 2 of CHAPTER 1.) is 122 not enabled or print_state callback is supplied, the output of 123 state ABI is same with switch class.