Add support for userspace using poll() for POLL_PRI on the sysfs brightness
attr to watch for brightness changes.
This commit adds a led_notify_brightness_change helper function for
waking up any poll() waiters; and calls this after any brightness changes
(after any led_classdev->brightness_set[_blocking] calls have completed).
In some use-cases led hardware may autonomously change its brightness,
e.g. the keyboard backlight used on some laptops is controlled by a
hardwired (firmware handled) hotkey. led_notify_brightness_change is
exported for use by drivers which can detect such autonomous changes.
This commit also updates the Documentation/ABI/testing/sysfs-class-led
documentation to document that userspace may now poll on the brightness
attribute.
Signed-off-by: Hans de Goede <hdego...@redhat.com>
---
Changes in v2:
-Wakeup / notify userspace on any brightness changes, not just on
autonomous changes done by the hw
Changes in v3:
-Rebase on linux-leds/for-next
Changes in v4:
-No Changes
---
Documentation/ABI/testing/sysfs-class-led | 8 ++++++--
drivers/leds/led-class.c | 9 +++++++++
drivers/leds/led-core.c | 16 +++++++++++++++-
include/linux/leds.h | 12 ++++++++++++
4 files changed, 42 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-class-led
b/Documentation/ABI/testing/sysfs-class-led
index 491cdee..0af5191 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -1,12 +1,16 @@
What: /sys/class/leds/<led>/brightness
-Date: March 2006
-KernelVersion: 2.6.17
+Date: March 2006 (poll October 2016)
+KernelVersion: 2.6.17 (poll since 4.10)
Contact: Richard Purdie <rpur...@rpsys.net>
Description:
Set the brightness of the LED. Most LEDs don't
have hardware brightness support, so will just be turned on for
non-zero brightness settings. The value is between 0 and
/sys/class/leds/<led>/max_brightness.
+ The file supports poll() to detect brightness changes, in
+ some cases the hardware / firmware may change the brightness
+ autonomously, poll() should be woken up in this case too,
+ but not all drivers may support this.
Writing 0 to this file clears active trigger.
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 731e4eb..c8d2d67 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -204,6 +204,14 @@ 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));
+ led_cdev->brightness_kn = sysfs_get_dirent(led_cdev->dev->kobj.sd,
+ "brightness");
+ if (!led_cdev->brightness_kn) {
+ dev_err(led_cdev->dev, "Error getting brightness
kernfs_node\n");
+ device_unregister(led_cdev->dev);
+ return -ENODEV;
+ }
+
#ifdef CONFIG_LEDS_TRIGGERS
init_rwsem(&led_cdev->trigger_lock);
#endif
@@ -255,6 +263,7 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
flush_work(&led_cdev->set_brightness_work);
+ sysfs_put(led_cdev->brightness_kn);
device_unregister(led_cdev->dev);
down_write(&leds_list_lock);
diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 2d0c75a..af78279 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -33,16 +33,24 @@ static int __led_set_brightness(struct led_classdev
*led_cdev,
led_cdev->brightness_set(led_cdev, value);
+ led_notify_brightness_change(led_cdev);
+
return 0;
}
static int __led_set_brightness_blocking(struct led_classdev *led_cdev,
enum led_brightness value)
{
+ int ret;
+
if (!led_cdev->brightness_set_blocking)
return -ENOTSUPP;
- return led_cdev->brightness_set_blocking(led_cdev, value);
+ ret = led_cdev->brightness_set_blocking(led_cdev, value);
+ if (ret >= 0)
+ led_notify_brightness_change(led_cdev);
+
+ return ret;
}
static void led_timer_function(unsigned long data)
@@ -308,6 +316,12 @@ int led_update_brightness(struct led_classdev *led_cdev)
}
EXPORT_SYMBOL_GPL(led_update_brightness);
+void led_notify_brightness_change(struct led_classdev *led_cdev)
+{
+ sysfs_notify_dirent(led_cdev->brightness_kn);
+}
+EXPORT_SYMBOL_GPL(led_notify_brightness_change);
+
/* Caller must ensure led_cdev->led_access held */
void led_sysfs_disable(struct led_classdev *led_cdev)
{
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 52993de..f034c2d 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>
@@ -93,6 +94,8 @@ struct led_classdev {
struct work_struct set_brightness_work;
+ struct kernfs_node *brightness_kn;
+
#ifdef CONFIG_LEDS_TRIGGERS
/* Protects the trigger data below */
struct rw_semaphore trigger_lock;
@@ -192,6 +195,15 @@ extern int led_set_brightness_sync(struct led_classdev
*led_cdev,
extern int led_update_brightness(struct led_classdev *led_cdev);
/**
+ * led_notify_brightness_change - Notify userspace of brightness changes
+ * @led_cdev: the LED to do the notify on
+ *
+ * Let any users waiting for POLL_PRI on the led's brightness sysfs
+ * atrribute know that the brightness has been changed.
+ */
+extern void led_notify_brightness_change(struct led_classdev *led_cdev);
+
+/**
* led_sysfs_disable - disable LED sysfs interface
* @led_cdev: the LED to set
*
--
2.9.3
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