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leds: add new transient trigger for one shot timer activation

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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.

As a specific example of this use-case, let's look at vibrate feature on
phones.  Vibrate function on phones is implemented using PWM pins on SoC
or PMIC.  There is a need to activate one shot timer to control the
vibrate feature, to prevent user space crashes leaving the phone in
vibrate mode permanently causing the battery to drain.

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.

Signed-off-by: Shuah Khan <shuahkhan@gmail.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: NeilBrown <neilb@suse.de>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Shuah Khan 2012-05-29 15:07:30 -07:00 committed by Linus Torvalds
parent 49dca5aebf
commit 44e1e9f8e7
4 changed files with 398 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

152
Documentation/leds/ledtrig-transient.txt Normal file
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@ -0,0 +1,152 @@
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.
As a specific example of this use-case, let's look at vibrate feature on
phones. Vibrate function on phones is implemented using PWM pins on SoC or
PMIC. There is a need to activate one shot timer to control the vibrate
feature, to prevent user space crashes leaving the phone in vibrate mode
permanently causing the battery to drain.
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.
Example 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 for the following example use cases:
- Control of vibrate (phones, tablets etc.) hardware by user space app.
- 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.

8
drivers/leds/Kconfig
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@ -479,4 +479,12 @@ config LEDS_TRIGGER_DEFAULT_ON
comment "iptables trigger is under Netfilter config (LED target)"
depends on LEDS_TRIGGERS
config LEDS_TRIGGER_TRANSIENT
tristate "LED Transient Trigger"
depends on LEDS_TRIGGERS
help
This allows one time activation of a transient state on
GPIO/PWM based hadrware.
If unsure, say Y.
endif # NEW_LEDS

1
drivers/leds/Makefile
View File

@ -57,3 +57,4 @@ obj-$(CONFIG_LEDS_TRIGGER_HEARTBEAT) += ledtrig-heartbeat.o
obj-$(CONFIG_LEDS_TRIGGER_BACKLIGHT) += ledtrig-backlight.o
obj-$(CONFIG_LEDS_TRIGGER_GPIO) += ledtrig-gpio.o
obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON) += ledtrig-default-on.o
obj-$(CONFIG_LEDS_TRIGGER_TRANSIENT) += ledtrig-transient.o

237
drivers/leds/ledtrig-transient.c Normal file
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@ -0,0 +1,237 @@
/*
* LED Kernel Transient Trigger
*
* Copyright (C) 2012 Shuah Khan <shuahkhan@gmail.com>
*
* Based on Richard Purdie's ledtrig-timer.c and Atsushi Nemoto's
* ledtrig-heartbeat.c
* Design and use-case input from Jonas Bonn <jonas@southpole.se> and
* Neil Brown <neilb@suse.de>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
/*
* Transient trigger allows one shot timer activation. Please refer to
* Documentation/leds/ledtrig-transient.txt for details
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/leds.h>
#include "leds.h"
struct transient_trig_data {
int activate;
int state;
int restore_state;
unsigned long duration;
struct timer_list timer;
};
static void transient_timer_function(unsigned long data)
{
struct led_classdev *led_cdev = (struct led_classdev *) data;
struct transient_trig_data *transient_data = led_cdev->trigger_data;
transient_data->activate = 0;
led_set_brightness(led_cdev, transient_data->restore_state);
}
static ssize_t transient_activate_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
return sprintf(buf, "%d\n", transient_data->activate);
}
static ssize_t transient_activate_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t size)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
unsigned long state;
ssize_t ret;
ret = kstrtoul(buf, 10, &state);
if (ret)
return ret;
if (state != 1 && state != 0)
return -EINVAL;
/* cancel the running timer */
if (state == 0 && transient_data->activate == 1) {
del_timer(&transient_data->timer);
transient_data->activate = state;
led_set_brightness(led_cdev, transient_data->restore_state);
return size;
}
/* start timer if there is no active timer */
if (state == 1 && transient_data->activate == 0 &&
transient_data->duration != 0) {
transient_data->activate = state;
led_set_brightness(led_cdev, transient_data->state);
transient_data->restore_state =
(transient_data->state == LED_FULL) ? LED_OFF : LED_FULL;
mod_timer(&transient_data->timer,
jiffies + transient_data->duration);
}
/* state == 0 && transient_data->activate == 0
timer is not active - just return */
/* state == 1 && transient_data->activate == 1
timer is already active - just return */
return size;
}
static ssize_t transient_duration_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
return sprintf(buf, "%lu\n", transient_data->duration);
}
static ssize_t transient_duration_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t size)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
unsigned long state;
ssize_t ret;
ret = kstrtoul(buf, 10, &state);
if (ret)
return ret;
transient_data->duration = state;
return size;
}
static ssize_t transient_state_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
int state;
state = (transient_data->state == LED_FULL) ? 1 : 0;
return sprintf(buf, "%d\n", state);
}
static ssize_t transient_state_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t size)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
struct transient_trig_data *transient_data = led_cdev->trigger_data;
unsigned long state;
ssize_t ret;
ret = kstrtoul(buf, 10, &state);
if (ret)
return ret;
if (state != 1 && state != 0)
return -EINVAL;
transient_data->state = (state == 1) ? LED_FULL : LED_OFF;
return size;
}
static DEVICE_ATTR(activate, 0644, transient_activate_show,
transient_activate_store);
static DEVICE_ATTR(duration, 0644, transient_duration_show,
transient_duration_store);
static DEVICE_ATTR(state, 0644, transient_state_show, transient_state_store);
static void transient_trig_activate(struct led_classdev *led_cdev)
{
int rc;
struct transient_trig_data *tdata;
tdata = kzalloc(sizeof(struct transient_trig_data), GFP_KERNEL);
if (!tdata) {
dev_err(led_cdev->dev,
"unable to allocate transient trigger\n");
return;
}
led_cdev->trigger_data = tdata;
rc = device_create_file(led_cdev->dev, &dev_attr_activate);
if (rc)
goto err_out;
rc = device_create_file(led_cdev->dev, &dev_attr_duration);
if (rc)
goto err_out_duration;
rc = device_create_file(led_cdev->dev, &dev_attr_state);
if (rc)
goto err_out_state;
setup_timer(&tdata->timer, transient_timer_function,
(unsigned long) led_cdev);
led_cdev->activated = true;
return;
err_out_state:
device_remove_file(led_cdev->dev, &dev_attr_duration);
err_out_duration:
device_remove_file(led_cdev->dev, &dev_attr_activate);
err_out:
dev_err(led_cdev->dev, "unable to register transient trigger\n");
led_cdev->trigger_data = NULL;
kfree(tdata);
}
static void transient_trig_deactivate(struct led_classdev *led_cdev)
{
struct transient_trig_data *transient_data = led_cdev->trigger_data;
if (led_cdev->activated) {
del_timer_sync(&transient_data->timer);
led_set_brightness(led_cdev, transient_data->restore_state);
device_remove_file(led_cdev->dev, &dev_attr_activate);
device_remove_file(led_cdev->dev, &dev_attr_duration);
device_remove_file(led_cdev->dev, &dev_attr_state);
led_cdev->trigger_data = NULL;
led_cdev->activated = false;
kfree(transient_data);
}
}
static struct led_trigger transient_trigger = {
.name = "transient",
.activate = transient_trig_activate,
.deactivate = transient_trig_deactivate,
};
static int __init transient_trig_init(void)
{
return led_trigger_register(&transient_trigger);
}
static void __exit transient_trig_exit(void)
{
led_trigger_unregister(&transient_trigger);
}
module_init(transient_trig_init);
module_exit(transient_trig_exit);
MODULE_AUTHOR("Shuah Khan <shuahkhan@gmail.com>");
MODULE_DESCRIPTION("Transient LED trigger");
MODULE_LICENSE("GPL");