3e971dbc7e
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
125 lines
4.9 KiB
Plaintext
125 lines
4.9 KiB
Plaintext
|
|
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.
|