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>

2 files changed, 42 insertions, 5 deletions

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index cf3a6d4d9475..659448ead685 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -152,7 +152,11 @@ config LEDS_TRIGGER_TIMER
         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 ed9ff02c77ea..82c55d6e4902 100644
--- a/drivers/leds/ledtrig-timer.c
+++ b/drivers/leds/ledtrig-timer.c
@@ -77,8 +77,21 @@ static ssize_t led_delay_on_store(struct device *dev,
                 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 @@ static ssize_t led_delay_off_store(struct device *dev,
                 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 @@ static void timer_trig_activate(struct led_classdev *led_cdev)
         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: