[RFC,v4,1/8] leds: add support for hardware driven LEDs

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index cd155ead8703..0175954717a3 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -169,6 +169,38 @@  Setting the brightness to zero with brightness_set() callback function
 should completely turn off the LED and cancel the previously programmed
 hardware blinking function, if any.
 
+Hardware driven LEDs
+===================================
+
+Some LEDs can be driven by hardware (for example a LED connected to
+an ethernet PHY or an ethernet switch can be configured to blink on activity on
+the network, which in software is done by the netdev trigger).
+
+To do such offloading, LED driver must support this and a supported trigger must
+be used.
+
+LED driver should declare the correct control mode supported and should set
+the LED_SOFTWARE_CONTROLLED or LED_HARDWARE_CONTROLLED bit in the flags
+parameter.
+The trigger will check these bit and fail to activate if the control mode
+is not supported. By default if a LED driver doesn't declare a control mode,
+bit LED_SOFTWARE_CONTROLLED is assumed and set by default.
+
+The LED must implement 3 main API:
+- hw_control_status(): This asks the LED driver if hardware mode is enabled
+    or not.
+- hw_control_start(): This will simply enable the hardware mode for the LED
+    and the LED driver should reset any active blink_mode.
+- hw_control_stop(): This will simply disable the hardware mode for the LED.
+    It's advised to the driver to put the LED in the old state but this is not
+    enforcerd and putting the LED off is also accepted.
+
+If LED_HARDWARE_CONTROLLED bit is the only contro mode set (LED_SOFTWARE_CONTROLLED
+not set) set hw_control_status/start/stop is optional as the LED supports only
+hardware mode and any software only trigger will reject activation.
+
+On init a LED driver that support a hardware mode should reset every blink mode
+set by default.
 
 Known Issues
 ============
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index ed800f5da7d8..bd2b19cc77ec 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -49,6 +49,17 @@  config LEDS_BRIGHTNESS_HW_CHANGED
 
 	  See Documentation/ABI/testing/sysfs-class-led for details.
 
+config LEDS_HARDWARE_CONTROL
+	bool "LED Hardware Control support"
+	help
+	  This option enabled Hardware control support used by leds that
+	  can be driven in hardware by using supported triggers.
+
+	  Hardware blink modes will be exposed by sysfs class in
+	  /sys/class/leds based on the trigger currently active.
+
+	  If unsure, say Y.
+
 comment "LED drivers"
 
 config LEDS_88PM860X
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index f4bb02f6e042..98a4dc889344 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -164,6 +164,26 @@  static void led_remove_brightness_hw_changed(struct led_classdev *led_cdev)
 }
 #endif
 
+#ifdef CONFIG_LEDS_HARDWARE_CONTROL
+static int led_classdev_check_hw_control_functions(struct led_classdev *led_cdev)
+{
+	if ((LED_SOFTWARE_CONTROLLED & led_cdev->flags) &&
+	    (LED_HARDWARE_CONTROLLED & led_cdev->flags) &&
+	    (!led_cdev->hw_control_status ||
+	    !led_cdev->hw_control_start ||
+	    !led_cdev->hw_control_stop))
+		return -EINVAL;
+
+	if ((LED_SOFTWARE_CONTROLLED & led_cdev->flags) &&
+	    (led_cdev->hw_control_status ||
+	    led_cdev->hw_control_start ||
+	    led_cdev->hw_control_stop))
+		return -EINVAL;
+
+	return 0;
+}
+#endif
+
 /**
  * led_classdev_suspend - suspend an led_classdev.
  * @led_cdev: the led_classdev to suspend.
@@ -367,6 +387,19 @@  int led_classdev_register_ext(struct device *parent,
 	if (ret < 0)
 		return ret;
 
+	/* Make sure a control mode is set.
+	 * With no control mode declared, set SOFTWARE_CONTROLLED by default.
+	 */
+	if (!(LED_SOFTWARE_CONTROLLED & led_cdev->flags) &&
+	    !(LED_HARDWARE_CONTROLLED & led_cdev->flags))
+		led_cdev->flags |= LED_SOFTWARE_CONTROLLED;
+
+#ifdef CONFIG_LEDS_HARDWARE_CONTROL
+	ret = led_classdev_check_hw_control_functions(led_cdev);
+	if (ret < 0)
+		return ret;
+#endif
+
 	mutex_init(&led_cdev->led_access);
 	mutex_lock(&led_cdev->led_access);
 	led_cdev->dev = device_create_with_groups(leds_class, parent, 0,
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 072491d3e17b..69dff5a29bea 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -154,6 +154,20 @@  ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
 }
 EXPORT_SYMBOL_GPL(led_trigger_read);
 
+static bool led_trigger_is_supported(struct led_classdev *led_cdev,
+				     struct led_trigger *trigger)
+{
+	if (trigger->supported_blink_modes == SOFTWARE_ONLY &&
+	    !(LED_SOFTWARE_CONTROLLED & led_cdev->flags))
+		return 0;
+
+	if (trigger->supported_blink_modes == HARDWARE_ONLY &&
+	    !(LED_HARDWARE_CONTROLLED & led_cdev->flags))
+		return 0;
+
+	return 1;
+}
+
 /* Caller must ensure led_cdev->trigger_lock held */
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 {
@@ -179,6 +193,10 @@  int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 
 		cancel_work_sync(&led_cdev->set_brightness_work);
 		led_stop_software_blink(led_cdev);
+		/* Disable hardware mode on trigger change if supported */
+		if ((led_cdev->flags & LED_HARDWARE_CONTROLLED) &&
+		    led_cdev->hw_control_status(led_cdev))
+			led_cdev->hw_control_stop(led_cdev);
 		if (led_cdev->trigger->deactivate)
 			led_cdev->trigger->deactivate(led_cdev);
 		device_remove_groups(led_cdev->dev, led_cdev->trigger->groups);
@@ -188,6 +206,10 @@  int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		led_set_brightness(led_cdev, LED_OFF);
 	}
 	if (trig) {
+		/* Make sure the trigger support the LED blink mode */
+		if (!led_trigger_is_supported(led_cdev, trig))
+			return -EINVAL;
+
 		spin_lock(&trig->leddev_list_lock);
 		list_add_tail_rcu(&led_cdev->trig_list, &trig->led_cdevs);
 		spin_unlock(&trig->leddev_list_lock);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index ba4861ec73d3..d64e5768e7ab 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -85,6 +85,11 @@  struct led_classdev {
 #define LED_BRIGHT_HW_CHANGED	BIT(21)
 #define LED_RETAIN_AT_SHUTDOWN	BIT(22)
 #define LED_INIT_DEFAULT_TRIGGER BIT(23)
+/* LED can be controlled by software. This is set by default
+ * if the LED driver doesn't report SOFTWARE or HARDWARE
+ */
+#define LED_SOFTWARE_CONTROLLED	BIT(24)
+#define LED_HARDWARE_CONTROLLED	BIT(25)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;
@@ -154,6 +159,20 @@  struct led_classdev {
 
 	/* LEDs that have private triggers have this set */
 	struct led_hw_trigger_type	*trigger_type;
+
+#ifdef CONFIG_LEDS_HARDWARE_CONTROL
+	/* Ask the LED driver if hardware mode is enabled or not.
+	 * Triggers will check if the hardware mode is active or not.
+	 */
+	bool			(*hw_control_status)(struct led_classdev *led_cdev);
+	/* Set LED in hardware mode and reset any blink mode active by default.
+	 */
+	int			(*hw_control_start)(struct led_classdev *led_cdev);
+	/* Disable hardware mode for LED. It's advised to the LED driver to put it to
+	 * the old status but that is not mandatory and also putting it off is accepted.
+	 */
+	int			(*hw_control_stop)(struct led_classdev *led_cdev);
+#endif
 #endif
 
 #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
@@ -215,7 +234,6 @@  extern struct led_classdev *of_led_get(struct device_node *np, int index);
 extern void led_put(struct led_classdev *led_cdev);
 struct led_classdev *__must_check devm_of_led_get(struct device *dev,
 						  int index);
-
 /**
  * led_blink_set - set blinking with software fallback
  * @led_cdev: the LED to start blinking
@@ -350,12 +368,26 @@  static inline bool led_sysfs_is_disabled(struct led_classdev *led_cdev)
 
 #define TRIG_NAME_MAX 50
 
+enum led_trigger_blink_supported_modes {
+	SOFTWARE_ONLY = BIT(0),
+	HARDWARE_ONLY = BIT(1),
+	SOFTWARE_HARDWARE = BIT(2),
+};
+
 struct led_trigger {
 	/* Trigger Properties */
 	const char	 *name;
 	int		(*activate)(struct led_classdev *led_cdev);
 	void		(*deactivate)(struct led_classdev *led_cdev);
 
+	/* Declare if the Trigger supports hardware control to
+	 * offload triggers or supports only software control.
+	 * A trigger can also declare support for hardware control
+	 * if is task is only configure LED blink modes and expose
+	 * them in sysfs.
+	 */
+	enum led_trigger_blink_supported_modes supported_blink_modes;
+
 	/* LED-private triggers have this set */
 	struct led_hw_trigger_type *trigger_type;