[PATCH ] leds: add new transient trigger for one shot timer support

[Shuah Khan <shuahkhan@gmail.com>]

This patch adds a new transient trigger for one shot timer support and is
to be used for the following example use cases:

- Control of vibrate (phones, tablets etc.) hardware by userspace app.
- Use of LED by userspace app as activity indicator.
- Use of LED by userspace 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 userspace app that needs a transient GPIO output

Transient trigger exports two attributes:
       transient_enabled -     one shot timer enable mechanism.
                               1 when enabled, 0 when disabled.
                               enabled state indicates a timer
                               with a value of transient_time running.
                               disabled state indicates no active timer
                               running.
       transient_time -        one shot timer value. When transient_enabled
                               is set, transient_time value is used to start
                               a timer that runs once.
       When timer expires transient_enabled goes back to disabled state,
       transient_time is left at the set value to be used when transient
       is enabled at a future time. This will allow user app to set the
       time once and enable it to run it once for the specified value as
       needed.

>From 80a15b18f6758d2890dfa6b266f2ea4e30338e3c Mon Sep 17 00:00:00 2001
From: Shuah Khan <shuahkhan@gmail.com>
Date: Thu, 19 Apr 2012 21:05:36 -0600
Subject: [PATCH 2/2] leds: add new transient trigger for one shot timer
 support


Signed-off-by: Shuah Khan <shuahkhan@gmail.com>
---
 drivers/leds/Kconfig             |    8 ++
 drivers/leds/Makefile            |    1 +
 drivers/leds/ledtrig-transient.c |  246 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 255 insertions(+), 0 deletions(-)
 create mode 100644 drivers/leds/ledtrig-transient.c

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index 589ba02..c6d8006 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -478,4 +478,12 @@ 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 enable of a transient state on GPIO/PWM based
+	  hadrware.
+	  If unsure, say Y.
+
 endif # NEW_LEDS
diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
index fa0f428..48d5af7 100644
--- a/drivers/leds/Makefile
+++ b/drivers/leds/Makefile
@@ -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
diff --git a/drivers/leds/ledtrig-transient.c b/drivers/leds/ledtrig-transient.c
new file mode 100644
index 0000000..e829124
--- /dev/null
+++ b/drivers/leds/ledtrig-transient.c
@@ -0,0 +1,246 @@
+/*
+ * 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>
+ *
+ * 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.
+ *
+ */
+/*
+* This trigger is intended to be used for the following example use cases:
+
+* - Control of vibrate (phones, tablets etc.) hardware by userspace app.
+* - Use of LED by userspace app as activity indicator.
+* - Use of LED by userspace 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 userspace app that needs a transient GPIO output.
+*
+* Transient trigger exports two attributes:
+*	transient_enabled -	one shot timer enable mechanism.
+*				1 when enabled, 0 when disabled.
+*				enabled state indicates a timer
+*				with a value of transient_time running.
+*				disabled state indicates no active timer
+*				running.
+*	transient_time -	one shot timer value. When transient_enabled
+*				is set, transient_time value is used to start
+*				a timer that runs once.
+*	When timer expires transient_enabled goes back to disabled state,
+*	transient_time is left at the set value to be used when transient
+*	is enabled at a future time. This will allow user app to set the
+*	time once and enable it to run it once for the specified value as
+*	needed.
+*
+*	echo 1 > transient_enabled - starts timer = transient_time when
+*				     transient_time is not 0.
+*	echo 0 > transient_enabled - cancels currently running timer.
+*	echo n > transient_time	   - stores timer value to be used upon next
+*				     enable. Currently active timer if any,
+*				     continues to run for the specified time.
+*	echo 0 > transient_time	   - stores timer value to be used upon next
+*				     enable. Currently active timer if any,
+*				     continues to run for the specified time.
+*
+*	Future enhancements:
+*	1. extending and shortening the timer could be supported either by
+*	   simply modifying the running timer transient_timer is set when
+*	   transient_enabled is in enabled state. For example:
+*	   echo n > transient_time will extend/shorten timer, however this
+*	   could lead race condtions with timer expiry.
+*	2. The same could be done using a third attribute to control
+*	   extending and shortening the timer.
+*
+*	Example use-cases:
+*	echo transient > trigger
+*	echo n > transient_time
+*	repeat the following step as needed:
+*	echo 1 > transient_enabled - start timer = transient_time to run once
+*	echo 1 > transient_enabled - start timer = transient_time to run once
+*	echo none > trigger
+*/
+
+#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 transient_enabled;
+	unsigned long transient_time;
+	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;
+
+	if (transient_data->transient_enabled) {
+		transient_data->transient_enabled = 0;
+		led_cdev->brightness_set(led_cdev, LED_OFF);
+		del_timer(&transient_data->timer);
+	}
+}
+
+static ssize_t led_transient_enabled_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->transient_enabled);
+}
+
+static ssize_t led_transient_enabled_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 = -EINVAL;
+
+	ret = kstrtoul(buf, 10, &state);
+	if (ret)
+		return ret;
+
+	if (state != 1 && state != 0)
+		return ret;
+
+	/* cancel the running timer */
+	if (state == 0) {
+		transient_timer_function((unsigned long) led_cdev);
+		return size;
+	}
+
+	transient_data->transient_enabled = (int) state;
+
+	/* start timer with transient_time value */
+	if (state == 1 && transient_data->transient_time != 0) {
+		led_cdev->brightness_set(led_cdev, LED_FULL);
+		mod_timer(&transient_data->timer,
+			  jiffies + transient_data->transient_time);
+	}
+
+	return size;
+}
+
+static ssize_t led_transient_time_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->transient_time);
+}
+
+static ssize_t led_transient_time_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 = -EINVAL;
+
+	ret = kstrtoul(buf, 10, &state);
+	if (ret)
+		return ret;
+
+	transient_data->transient_time = state;
+
+	return size;
+}
+
+static DEVICE_ATTR(transient_enabled, 0644, led_transient_enabled_show,
+		   led_transient_enabled_store);
+static DEVICE_ATTR(transient_time, 0644, led_transient_time_show,
+		   led_transient_time_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_transient_enabled);
+	if (rc)
+		goto err_out;
+
+	rc = device_create_file(led_cdev->dev, &dev_attr_transient_time);
+	if (rc)
+		goto err_out_time;
+
+	setup_timer(&tdata->timer, transient_timer_function,
+		    (unsigned long) led_cdev);
+	led_cdev->activated = true;
+
+	printk(KERN_DEBUG "Ativated led transient trigger %s\n",
+		led_cdev->name);
+
+	return;
+
+err_out_time:
+	device_remove_file(led_cdev->dev, &dev_attr_transient_enabled);
+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) {
+		device_remove_file(led_cdev->dev, &dev_attr_transient_enabled);
+		device_remove_file(led_cdev->dev, &dev_attr_transient_time);
+		del_timer_sync(&transient_data->timer);
+		led_cdev->trigger_data = NULL;
+		led_cdev->activated = false;
+		kfree(transient_data);
+	}
+	printk(KERN_DEBUG "Deativated led transient trigger %s\n",
+		led_cdev->name);
+}
+
+static struct led_trigger transient_trigger = {
+	.name     = "transient",
+	.activate = transient_trig_activate,
+	.deactivate = transient_trig_deactivate,
+};
+
+static int __init transient_trig_init(void)
+{
+	printk(KERN_DEBUG "Registered led transient trigger\n");
+	return led_trigger_register(&transient_trigger);
+}
+
+static void __exit transient_trig_exit(void)
+{
+	led_trigger_unregister(&transient_trigger);
+	printk(KERN_DEBUG "Unregistered led transient trigger\n");
+}
+
+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");
-- 
1.7.5.4