leds: Add support for hardware accelerated LED flashing
Extends the leds subsystem with a blink_set() callback function which can
be optionally implemented by a LED driver. If implemented, the driver can use
the hardware acceleration for blinking a LED.
Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt
index 877af6ef..56757c7 100644
--- a/Documentation/leds-class.txt
+++ b/Documentation/leds-class.txt
@@ -48,6 +48,26 @@
of the name don't apply, just leave that section blank.
+Hardware accelerated blink of LEDs
+==================================
+
+Some LEDs can be programmed to blink without any CPU interaction. To
+support this feature, a LED driver can optionally implement the
+blink_set() function (see <linux/leds.h>). If implemeted, triggers can
+attempt to use it before falling back to software timers. The blink_set()
+function should return 0 if the blink setting is supported, or -EINVAL
+otherwise, which means that LED blinking will be handled by software.
+
+The blink_set() function should choose a user friendly blinking
+value if it is called with *delay_on==0 && *delay_off==0 parameters. In
+this case the driver should give back the chosen value through delay_on
+and delay_off parameters to the leds subsystem.
+
+Any call to the brightness_set() callback function should cancel the
+previously programmed hardware blinking function so setting the brightness
+to 0 can also cancel the blinking of the LED.
+
+
Known Issues
============
@@ -56,10 +76,6 @@
compared to the benefits the simple trigger functionality brings. The
rest of the LED subsystem can be modular.
-Some leds can be programmed to flash in hardware. As this isn't a generic
-LED device property, this should be exported as a device specific sysfs
-attribute rather than part of the class if this functionality is required.
-
Future Development
==================
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index cf3a6d4..659448e 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -152,7 +152,11 @@
depends on LEDS_TRIGGERS
help
This allows LEDs to be controlled by a programmable timer
- via sysfs. If unsure, say Y.
+ via sysfs. Some LED hardware can be programmed to start
+ blinking the LED without any further software interaction.
+ For more details read Documentation/leds-class.txt.
+
+ If unsure, say Y.
config LEDS_TRIGGER_IDE_DISK
bool "LED IDE Disk Trigger"
diff --git a/drivers/leds/ledtrig-timer.c b/drivers/leds/ledtrig-timer.c
index ed9ff02..82c55d6 100644
--- a/drivers/leds/ledtrig-timer.c
+++ b/drivers/leds/ledtrig-timer.c
@@ -77,8 +77,21 @@
count++;
if (count == size) {
- timer_data->delay_on = state;
- mod_timer(&timer_data->timer, jiffies + 1);
+ if (timer_data->delay_on != state) {
+ /* the new value differs from the previous */
+ timer_data->delay_on = state;
+
+ /* deactivate previous settings */
+ del_timer_sync(&timer_data->timer);
+
+ /* try to activate hardware acceleration, if any */
+ if (!led_cdev->blink_set ||
+ led_cdev->blink_set(led_cdev,
+ &timer_data->delay_on, &timer_data->delay_off)) {
+ /* no hardware acceleration, blink via timer */
+ mod_timer(&timer_data->timer, jiffies + 1);
+ }
+ }
ret = count;
}
@@ -110,8 +123,21 @@
count++;
if (count == size) {
- timer_data->delay_off = state;
- mod_timer(&timer_data->timer, jiffies + 1);
+ if (timer_data->delay_off != state) {
+ /* the new value differs from the previous */
+ timer_data->delay_off = state;
+
+ /* deactivate previous settings */
+ del_timer_sync(&timer_data->timer);
+
+ /* try to activate hardware acceleration, if any */
+ if (!led_cdev->blink_set ||
+ led_cdev->blink_set(led_cdev,
+ &timer_data->delay_on, &timer_data->delay_off)) {
+ /* no hardware acceleration, blink via timer */
+ mod_timer(&timer_data->timer, jiffies + 1);
+ }
+ }
ret = count;
}
@@ -143,6 +169,13 @@
if (rc)
goto err_out_delayon;
+ /* If there is hardware support for blinking, start one
+ * user friendly blink rate chosen by the driver.
+ */
+ if (led_cdev->blink_set)
+ led_cdev->blink_set(led_cdev,
+ &timer_data->delay_on, &timer_data->delay_off);
+
return;
err_out_delayon:
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 00f89fd..0201f6f 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -38,6 +38,11 @@
void (*brightness_set)(struct led_classdev *led_cdev,
enum led_brightness brightness);
+ /* Activate hardware accelerated blink */
+ int (*blink_set)(struct led_classdev *led_cdev,
+ unsigned long *delay_on,
+ unsigned long *delay_off);
+
struct device *dev;
struct list_head node; /* LED Device list */
char *default_trigger; /* Trigger to use */