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| -rw-r--r-- | Documentation/extcon/porting-android-switch-class | 124 |
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diff --git a/Documentation/extcon/porting-android-switch-class b/Documentation/extcon/porting-android-switch-class new file mode 100644 index 00000000000..eb0fa5f4fe8 --- /dev/null +++ b/Documentation/extcon/porting-android-switch-class @@ -0,0 +1,124 @@ + + Staging/Android Switch Class Porting Guide + (linux/drivers/staging/android/switch) + (c) Copyright 2012 Samsung Electronics + +AUTHORS +MyungJoo Ham <myungjoo.ham@samsung.com> + +/***************************************************************** + * CHAPTER 1. * + * PORTING SWITCH CLASS DEVICE DRIVERS * + *****************************************************************/ + +****** STEP 1. Basic Functionality + No extcon extended feature, but switch features only. + +- struct switch_dev (fed to switch_dev_register/unregister) + @name: no change + @dev: no change + @index: drop (not used in switch device driver side anyway) + @state: no change + If you have used @state with magic numbers, keep it + at this step. + @print_name: no change but type change (switch_dev->extcon_dev) + @print_state: no change but type change (switch_dev->extcon_dev) + +- switch_dev_register(sdev, dev) + => extcon_dev_register(edev, dev) + : no change but type change (sdev->edev) +- switch_dev_unregister(sdev) + => extcon_dev_unregister(edev) + : no change but type change (sdev->edev) +- switch_get_state(sdev) + => extcon_get_state(edev) + : no change but type change (sdev->edev) and (return: int->u32) +- switch_set_state(sdev, state) + => extcon_set_state(edev, state) + : no change but type change (sdev->edev) and (state: int->u32) + +With this changes, the ex-switch extcon class device works as it once +worked as switch class device. However, it will now have additional +interfaces (both ABI and in-kernel API) and different ABI locations. +However, if CONFIG_ANDROID is enabled without CONFIG_ANDROID_SWITCH, +/sys/class/switch/* will be symbolically linked to /sys/class/extcon/ +so that they are still compatible with legacy userspace processes. + +****** STEP 2. Multistate (no more magic numbers in state value) + Extcon's extended features for switch device drivers with + complex features usually required magic numbers in state + value of switch_dev. With extcon, such magic numbers that + support multiple cables ( + + 1. Define cable names at edev->supported_cable. + 2. (Recommended) remove print_state callback. + 3. Use extcon_get_cable_state_(edev, index) or + extcon_get_cable_state(edev, cable_name) instead of + extcon_get_state(edev) if you intend to get a state of a specific + cable. Same for set_state. This way, you can remove the usage of + magic numbers in state value. + 4. Use extcon_update_state() if you are updating specific bits of + the state value. + +Example: a switch device driver w/ magic numbers for two cables. + "0x00": no cables connected. + "0x01": cable 1 connected + "0x02": cable 2 connected + "0x03": cable 1 and 2 connected + 1. edev->supported_cable = {"1", "2", NULL}; + 2. edev->print_state = NULL; + 3. extcon_get_cable_state_(edev, 0) shows cable 1's state. + extcon_get_cable_state(edev, "1") shows cable 1's state. + extcon_set_cable_state_(edev, 1) sets cable 2's state. + extcon_set_cable_state(edev, "2") sets cable 2's state + 4. extcon_update_state(edev, 0x01, 0) sets the least bit's 0. + +****** STEP 3. Notify other device drivers + + You can notify others of the cable attach/detach events with +notifier chains. + + At the side of other device drivers (the extcon device itself +does not need to get notified of its own events), there are two +methods to register notifier_block for cable events: +(a) for a specific cable or (b) for every cable. + + (a) extcon_register_interest(obj, extcon_name, cable_name, nb) + Example: want to get news of "MAX8997_MUIC"'s "USB" cable + + obj = kzalloc(sizeof(struct extcon_specific_cable_nb), + GFP_KERNEL); + nb->notifier_call = the_callback_to_handle_usb; + + extcon_register_intereset(obj, "MAX8997_MUIC", "USB", nb); + + (b) extcon_register_notifier(edev, nb) + Call nb for any changes in edev. + + Please note that in order to properly behave with method (a), +the extcon device driver should support multistate feature (STEP 2). + +****** STEP 4. Inter-cable relation (mutually exclusive) + + You can provide inter-cable mutually exclusiveness information +for an extcon device. When cables A and B are declared to be mutually +exclusive, the two cables cannot be in ATTACHED state simulteneously. + + +/***************************************************************** + * CHAPTER 2. * + * PORTING USERSPACE w/ SWITCH CLASS DEVICE SUPPORT * + *****************************************************************/ + +****** ABI Location + + If "CONFIG_ANDROID" is enabled and "CONFIG_ANDROID_SWITCH" is +disabled, /sys/class/switch/* are created as symbolic links to +/sys/class/extcon/*. Because CONFIG_ANDROID_SWITCH creates +/sys/class/switch directory, we disable symboling linking if +CONFIG_ANDROID_SWITCH is enabled. + + The two files of switch class, name and state, are provided with +extcon, too. When the multistate support (STEP 2 of CHAPTER 1.) is +not enabled or print_state callback is supplied, the output of +state ABI is same with switch class. |