leds: class: Add new optional brightness_hw_changed attribute

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>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

2 files changed, 85 insertions, 0 deletions

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index c621cbbb5768..275f467956ee 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -29,6 +29,15 @@ config LEDS_CLASS_FLASH
 	  for the flash related features of a LED device. It can be built
 	  as a module.
 
+config LEDS_BRIGHTNESS_HW_CHANGED
+	bool "LED Class brightness_hw_changed attribute support"
+	depends on LEDS_CLASS
+	help
+	  This option enables support for the brightness_hw_changed attribute
+	  for led sysfs class devices under /sys/class/leds.
+
+	  See Documentation/ABI/testing/sysfs-class-led for details.
+
 comment "LED drivers"
 
 config LEDS_88PM860X
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 326ee6e925a2..f2b0a80a62b4 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -103,6 +103,68 @@ static const struct attribute_group *led_groups[] = {
 	NULL,
 };
 
+#ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
+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);
+
+	if (led_cdev->brightness_hw_changed == -1)
+		return -ENODATA;
+
+	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)
+{
+	if (WARN_ON(!led_cdev->brightness_hw_changed_kn))
+		return;
+
+	led_cdev->brightness_hw_changed = brightness;
+	sysfs_notify_dirent(led_cdev->brightness_hw_changed_kn);
+}
+EXPORT_SYMBOL_GPL(led_classdev_notify_brightness_hw_changed);
+#else
+static int led_add_brightness_hw_changed(struct led_classdev *led_cdev)
+{
+	return 0;
+}
+static void led_remove_brightness_hw_changed(struct led_classdev *led_cdev)
+{
+}
+#endif
+
 /**
  * led_classdev_suspend - suspend an led_classdev.
  * @led_cdev: the led_classdev to suspend.
@@ -204,10 +266,21 @@ 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);
 #endif
+#ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
+	led_cdev->brightness_hw_changed = -1;
+#endif
 	mutex_init(&led_cdev->led_access);
 	/* add to the list of leds */
 	down_write(&leds_list_lock);
@@ -256,6 +329,9 @@ 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);