[PATCH v6 1/4] leds: class: Add new optional brightness_hw_changed attribute

[Hans de Goede <hdegoede@redhat.com>]

Some LEDs may have their brightness level changed autonomously
(outside of kernel control) by hardware / firmware. This commit
adds support for an optional brightness_hw_changed attribute to
signal such changes to userspace (if a driver can detect them):

What:		/sys/class/leds/<led>/brightness_hw_changed
Date:		January 2017
KernelVersion:	4.11
Description:
		Last hardware set brightness level for this LED. Some LEDs
		may be changed autonomously by hardware/firmware. Only LEDs
		where this happens and the driver can detect this, will
		have this file.

		This file supports poll() to detect when the hardware
		changes the brightness.

		Reading this file will return the last brightness level set
		by the hardware, this may be different from the current
		brightness.

Drivers which want to support this, simply add LED_BRIGHT_HW_CHANGED to
their flags field and call led_classdev_notify_brightness_hw_changed()
with the hardware set brightness when they detect a hardware / firmware
triggered brightness change.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v6:
-New patch in v6 of this set, replacing previous trigger based API
---
 Documentation/ABI/testing/sysfs-class-led | 16 +++++++++
 drivers/leds/led-class.c                  | 57 +++++++++++++++++++++++++++++++
 include/linux/leds.h                      |  8 +++++
 3 files changed, 81 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
index 491cdee..9f6e75d 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -23,6 +23,22 @@ Description:
 		If the LED does not support different brightness levels, this
 		should be 1.
 
+What:		/sys/class/leds/<led>/brightness_hw_changed
+Date:		January 2017
+KernelVersion:	4.11
+Description:
+		Last hardware set brightness level for this LED. Some LEDs
+		may be changed autonomously by hardware/firmware. Only LEDs
+		where this happens and the driver can detect this, will have
+		this file.
+
+		This file supports poll() to detect when the hardware changes
+		the brightness.
+
+		Reading this file will return the last brightness level set
+		by the hardware, this may be different from the current
+		brightness.
+
 What:		/sys/class/leds/<led>/trigger
 Date:		March 2006
 KernelVersion:	2.6.17
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 326ee6e..27aa7b6 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -103,6 +103,52 @@ static const struct attribute_group *led_groups[] = {
 	NULL,
 };
 
+static ssize_t brightness_hw_changed_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%u\n", led_cdev->brightness_hw_changed);
+}
+
+static DEVICE_ATTR_RO(brightness_hw_changed);
+
+static int led_add_brightness_hw_changed(struct led_classdev *led_cdev)
+{
+	struct device *dev = led_cdev->dev;
+	int ret;
+
+	ret = device_create_file(dev, &dev_attr_brightness_hw_changed);
+	if (ret) {
+		dev_err(dev, "Error creating brightness_hw_changed\n");
+		return ret;
+	}
+
+	led_cdev->brightness_hw_changed_kn =
+		sysfs_get_dirent(dev->kobj.sd, "brightness_hw_changed");
+	if (!led_cdev->brightness_hw_changed_kn) {
+		dev_err(dev, "Error getting brightness_hw_changed kn\n");
+		device_remove_file(dev, &dev_attr_brightness_hw_changed);
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+static void led_remove_brightness_hw_changed(struct led_classdev *led_cdev)
+{
+	sysfs_put(led_cdev->brightness_hw_changed_kn);
+	device_remove_file(led_cdev->dev, &dev_attr_brightness_hw_changed);
+}
+
+void led_classdev_notify_brightness_hw_changed(struct led_classdev *led_cdev,
+					       enum led_brightness brightness)
+{
+	led_cdev->brightness_hw_changed = brightness;
+	sysfs_notify_dirent(led_cdev->brightness_hw_changed_kn);
+}
+EXPORT_SYMBOL_GPL(led_classdev_notify_brightness_hw_changed);
+
 /**
  * led_classdev_suspend - suspend an led_classdev.
  * @led_cdev: the led_classdev to suspend.
@@ -204,6 +250,14 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
 		dev_warn(parent, "Led %s renamed to %s due to name collision",
 				led_cdev->name, dev_name(led_cdev->dev));
 
+	if (led_cdev->flags & LED_BRIGHT_HW_CHANGED) {
+		ret = led_add_brightness_hw_changed(led_cdev);
+		if (ret) {
+			device_unregister(led_cdev->dev);
+			return ret;
+		}
+	}
+
 	led_cdev->work_flags = 0;
 #ifdef CONFIG_LEDS_TRIGGERS
 	init_rwsem(&led_cdev->trigger_lock);
@@ -256,6 +310,9 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
 
 	flush_work(&led_cdev->set_brightness_work);
 
+	if (led_cdev->flags & LED_BRIGHT_HW_CHANGED)
+		led_remove_brightness_hw_changed(led_cdev);
+
 	device_unregister(led_cdev->dev);
 
 	down_write(&leds_list_lock);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 569cb53..aa452c8 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -13,6 +13,7 @@
 #define __LINUX_LEDS_H_INCLUDED
 
 #include <linux/device.h>
+#include <linux/kernfs.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/rwsem.h>
@@ -35,6 +36,7 @@ struct led_classdev {
 	const char		*name;
 	enum led_brightness	 brightness;
 	enum led_brightness	 max_brightness;
+	enum led_brightness	 brightness_hw_changed;
 	int			 flags;
 
 	/* Lower 16 bits reflect status */
@@ -46,6 +48,7 @@ struct led_classdev {
 #define LED_DEV_CAP_FLASH	(1 << 18)
 #define LED_HW_PLUGGABLE	(1 << 19)
 #define LED_PANIC_INDICATOR	(1 << 20)
+#define LED_BRIGHT_HW_CHANGED	(1 << 21)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;
@@ -99,6 +102,9 @@ struct led_classdev {
 	struct work_struct	set_brightness_work;
 	int			delayed_set_value;
 
+	/* For LEDs with brightness_hw_changed sysfs attribute */
+	struct kernfs_node	*brightness_hw_changed_kn;
+
 #ifdef CONFIG_LEDS_TRIGGERS
 	/* Protects the trigger data below */
 	struct rw_semaphore	 trigger_lock;
@@ -123,6 +129,8 @@ extern void devm_led_classdev_unregister(struct device *parent,
 					 struct led_classdev *led_cdev);
 extern void led_classdev_suspend(struct led_classdev *led_cdev);
 extern void led_classdev_resume(struct led_classdev *led_cdev);
+extern void led_classdev_notify_brightness_hw_changed(
+	struct led_classdev *led_cdev, enum led_brightness brightness);
 
 /**
  * led_blink_set - set blinking with software fallback
-- 
2.9.3