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>

4 files changed, 67 insertions, 9 deletions

diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt
index 877af6efc18b..56757c751d6f 100644
--- a/Documentation/leds-class.txt
+++ b/Documentation/leds-class.txt
@@ -48,6 +48,26 @@ above leaves scope for further attributes should they be needed. If sections
 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 @@ would cause nightmare dependency issues. I see this as a minor issue
 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 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:
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 00f89fd6c52a..0201f6f51cea 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -38,6 +38,11 @@ struct led_classdev {
         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 */