Re: [PATCH v2 1/4] leds: core: Add support for poll()ing the sysfs brightness attr for changes.

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Hi,

On 24-10-16 22:43, Jacek Anaszewski wrote:
Hi Hans,

Thanks for the update.
Could you please rebase your patches onto recent linux-leds.git,
for-next branch?

Done, I will send a v3 soon (today or tomorrow).

Also it would be convenient to have sample application for polling
brightness changes in tools/leds.

I'm sorry but I do not have time to create such a sample application.

Regards,

Hans



Thanks,
Jacek Anaszewski

On 10/23/2016 09:46 PM, Hans de Goede wrote:
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 <hdegoede@xxxxxxxxxx>
---
Changes in v2:
-Wakeup / notify userspace on any brightness changes, not just on
 autonomous changes done by the hw
---
 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 86ace28..0685551 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 <rpurdie@xxxxxxxxx>
 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.

 What:        /sys/class/leds/<led>/max_brightness
 Date:        March 2006
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index aa84e5b..3427a65 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -203,6 +203,14 @@ 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
@@ -254,6 +262,7 @@ 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 3bce448..e2e5cc7 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 ddfcb2d..eebcd8c 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>
@@ -94,6 +95,8 @@ struct led_classdev {
     struct work_struct    set_brightness_work;
     int            delayed_set_value;

+    struct kernfs_node    *brightness_kn;
+
 #ifdef CONFIG_LEDS_TRIGGERS
     /* Protects the trigger data below */
     struct rw_semaphore     trigger_lock;
@@ -193,6 +196,15 @@ 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
  *

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