usb: Add LED triggers for USB activity

With this patch, USB activity can be signaled by blinking a LED. There
are two triggers, one for activity on USB host and one for USB gadget.

Both triggers should work with all host/device controllers. Tested only
with musb.

Performace: I measured performance overheads on ARM Cortex-A8 (TI
AM335x) running on 600 MHz.

Duration of usb_led_activity():
- with no LED attached to the trigger:        2 ± 1 µs
- with one GPIO LED attached to the trigger:  2 ± 1 µs or 8 ± 2 µs (two peaks in histogram)

Duration of functions calling usb_led_activity() (with this patch
applied and no LED attached to the trigger):
- __usb_hcd_giveback_urb():    10 - 25 µs
- usb_gadget_giveback_request(): 2 - 6 µs

Signed-off-by: Michal Sojka <sojka@merica.cz>
Acked-by: Felipe Balbi <balbi@ti.com>
Tested-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 58 insertions, 0 deletions

diff --git a/drivers/usb/common/Makefile b/drivers/usb/common/Makefile
index 052c12069c24..ca2f8bd0e431 100644
--- a/drivers/usb/common/Makefile
+++ b/drivers/usb/common/Makefile
@@ -4,5 +4,6 @@
 
 obj-$(CONFIG_USB_COMMON)          += usb-common.o
 usb-common-y                      += common.o
+usb-common-$(CONFIG_USB_LED_TRIG) += led.o
 
 obj-$(CONFIG_USB_OTG_FSM) += usb-otg-fsm.o
diff --git a/drivers/usb/common/led.c b/drivers/usb/common/led.c
new file mode 100644
index 000000000000..df23da00a901
--- /dev/null
+++ b/drivers/usb/common/led.c
@@ -0,0 +1,57 @@
+/*
+ * LED Triggers for USB Activity
+ *
+ * Copyright 2014 Michal Sojka <sojka@merica.cz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/leds.h>
+#include <linux/usb.h>
+
+#define BLINK_DELAY 30
+
+static unsigned long usb_blink_delay = BLINK_DELAY;
+
+DEFINE_LED_TRIGGER(ledtrig_usb_gadget);
+DEFINE_LED_TRIGGER(ledtrig_usb_host);
+
+void usb_led_activity(enum usb_led_event ev)
+{
+        struct led_trigger *trig = NULL;
+
+        switch (ev) {
+        case USB_LED_EVENT_GADGET:
+                trig = ledtrig_usb_gadget;
+                break;
+        case USB_LED_EVENT_HOST:
+                trig = ledtrig_usb_host;
+                break;
+        }
+        /* led_trigger_blink_oneshot() handles trig == NULL gracefully */
+        led_trigger_blink_oneshot(trig, &usb_blink_delay, &usb_blink_delay, 0);
+}
+EXPORT_SYMBOL_GPL(usb_led_activity);
+
+
+static int __init ledtrig_usb_init(void)
+{
+        led_trigger_register_simple("usb-gadget", &ledtrig_usb_gadget);
+        led_trigger_register_simple("usb-host", &ledtrig_usb_host);
+        return 0;
+}
+
+static void __exit ledtrig_usb_exit(void)
+{
+        led_trigger_unregister_simple(ledtrig_usb_gadget);
+        led_trigger_unregister_simple(ledtrig_usb_host);
+}
+
+module_init(ledtrig_usb_init);
+module_exit(ledtrig_usb_exit);