mirror of
https://github.com/torvalds/linux.git
synced 2024-12-01 00:21:32 +00:00
a2f8e2b4f1
Remove notes about vibrations, as that is better done using input subsystem. Signed-off-by: Pavel Machek <pavel@ucw.cz>
161 lines
6.9 KiB
ReStructuredText
161 lines
6.9 KiB
ReStructuredText
=====================
|
|
LED Transient Trigger
|
|
=====================
|
|
|
|
The leds timer trigger does not currently have an interface to activate
|
|
a one shot timer. The current support allows for setting two timers, one for
|
|
specifying how long a state to be on, and the second for how long the state
|
|
to be off. The delay_on value specifies the time period an LED should stay
|
|
in on state, followed by a delay_off value that specifies how long the LED
|
|
should stay in off state. The on and off cycle repeats until the trigger
|
|
gets deactivated. There is no provision for one time activation to implement
|
|
features that require an on or off state to be held just once and then stay in
|
|
the original state forever.
|
|
|
|
Without one shot timer interface, user space can still use timer trigger to
|
|
set a timer to hold a state, however when user space application crashes or
|
|
goes away without deactivating the timer, the hardware will be left in that
|
|
state permanently.
|
|
|
|
Transient trigger addresses the need for one shot timer activation. The
|
|
transient trigger can be enabled and disabled just like the other leds
|
|
triggers.
|
|
|
|
When an led class device driver registers itself, it can specify all leds
|
|
triggers it supports and a default trigger. During registration, activation
|
|
routine for the default trigger gets called. During registration of an led
|
|
class device, the LED state does not change.
|
|
|
|
When the driver unregisters, deactivation routine for the currently active
|
|
trigger will be called, and LED state is changed to LED_OFF.
|
|
|
|
Driver suspend changes the LED state to LED_OFF and resume doesn't change
|
|
the state. Please note that there is no explicit interaction between the
|
|
suspend and resume actions and the currently enabled trigger. LED state
|
|
changes are suspended while the driver is in suspend state. Any timers
|
|
that are active at the time driver gets suspended, continue to run, without
|
|
being able to actually change the LED state. Once driver is resumed, triggers
|
|
start functioning again.
|
|
|
|
LED state changes are controlled using brightness which is a common led
|
|
class device property. When brightness is set to 0 from user space via
|
|
echo 0 > brightness, it will result in deactivating the current trigger.
|
|
|
|
Transient trigger uses standard register and unregister interfaces. During
|
|
trigger registration, for each led class device that specifies this trigger
|
|
as its default trigger, trigger activation routine will get called. During
|
|
registration, the LED state does not change, unless there is another trigger
|
|
active, in which case LED state changes to LED_OFF.
|
|
|
|
During trigger unregistration, LED state gets changed to LED_OFF.
|
|
|
|
Transient trigger activation routine doesn't change the LED state. It
|
|
creates its properties and does its initialization. Transient trigger
|
|
deactivation routine, will cancel any timer that is active before it cleans
|
|
up and removes the properties it created. It will restore the LED state to
|
|
non-transient state. When driver gets suspended, irrespective of the transient
|
|
state, the LED state changes to LED_OFF.
|
|
|
|
Transient trigger can be enabled and disabled from user space on led class
|
|
devices, that support this trigger as shown below::
|
|
|
|
echo transient > trigger
|
|
echo none > trigger
|
|
|
|
NOTE:
|
|
Add a new property trigger state to control the state.
|
|
|
|
This trigger exports three properties, activate, state, and duration. When
|
|
transient trigger is activated these properties are set to default values.
|
|
|
|
- duration allows setting timer value in msecs. The initial value is 0.
|
|
- activate allows activating and deactivating the timer specified by
|
|
duration as needed. The initial and default value is 0. This will allow
|
|
duration to be set after trigger activation.
|
|
- state allows user to specify a transient state to be held for the specified
|
|
duration.
|
|
|
|
activate
|
|
- one shot timer activate mechanism.
|
|
1 when activated, 0 when deactivated.
|
|
default value is zero when transient trigger is enabled,
|
|
to allow duration to be set.
|
|
|
|
activate state indicates a timer with a value of specified
|
|
duration running.
|
|
deactivated state indicates that there is no active timer
|
|
running.
|
|
|
|
duration
|
|
- one shot timer value. When activate is set, duration value
|
|
is used to start a timer that runs once. This value doesn't
|
|
get changed by the trigger unless user does a set via
|
|
echo new_value > duration
|
|
|
|
state
|
|
- transient state to be held. It has two values 0 or 1. 0 maps
|
|
to LED_OFF and 1 maps to LED_FULL. The specified state is
|
|
held for the duration of the one shot timer and then the
|
|
state gets changed to the non-transient state which is the
|
|
inverse of transient state.
|
|
If state = LED_FULL, when the timer runs out the state will
|
|
go back to LED_OFF.
|
|
If state = LED_OFF, when the timer runs out the state will
|
|
go back to LED_FULL.
|
|
Please note that current LED state is not checked prior to
|
|
changing the state to the specified state.
|
|
Driver could map these values to inverted depending on the
|
|
default states it defines for the LED in its brightness_set()
|
|
interface which is called from the led brightness_set()
|
|
interfaces to control the LED state.
|
|
|
|
When timer expires activate goes back to deactivated state, duration is left
|
|
at the set value to be used when activate is set at a future time. This will
|
|
allow user app to set the time once and activate it to run it once for the
|
|
specified value as needed. When timer expires, state is restored to the
|
|
non-transient state which is the inverse of the transient state:
|
|
|
|
================= ===============================================
|
|
echo 1 > activate starts timer = duration when duration is not 0.
|
|
echo 0 > activate cancels currently running timer.
|
|
echo n > duration stores timer value to be used upon next
|
|
activate. Currently active timer if
|
|
any, continues to run for the specified time.
|
|
echo 0 > duration stores timer value to be used upon next
|
|
activate. Currently active timer if any,
|
|
continues to run for the specified time.
|
|
echo 1 > state stores desired transient state LED_FULL to be
|
|
held for the specified duration.
|
|
echo 0 > state stores desired transient state LED_OFF to be
|
|
held for the specified duration.
|
|
================= ===============================================
|
|
|
|
What is not supported
|
|
=====================
|
|
|
|
- Timer activation is one shot and extending and/or shortening the timer
|
|
is not supported.
|
|
|
|
Examples
|
|
========
|
|
|
|
use-case 1::
|
|
|
|
echo transient > trigger
|
|
echo n > duration
|
|
echo 1 > state
|
|
|
|
repeat the following step as needed::
|
|
|
|
echo 1 > activate - start timer = duration to run once
|
|
echo 1 > activate - start timer = duration to run once
|
|
echo none > trigger
|
|
|
|
This trigger is intended to be used for the following example use cases:
|
|
|
|
- Use of LED by user space app as activity indicator.
|
|
- Use of LED by user space app as a kind of watchdog indicator -- as
|
|
long as the app is alive, it can keep the LED illuminated, if it dies
|
|
the LED will be extinguished automatically.
|
|
- Use by any user space app that needs a transient GPIO output.
|