usb: core: added uevent for over-current

After commit 1cbd53c8 ("usb: core: introduce per-port over-current
counters") usb ports expose a sysfs value 'over_current_count'
to user space. This value on its own is not very useful as it requires
manual polling.

As a solution, fire a udev event from the usb hub device that specifies
the values 'OVER_CURRENT_PORT' and 'OVER_CURRENT_COUNT' that indicate
the path of the usb port where the over-current event occurred and the
value of 'over_current_count' in sysfs. Additionally, call
sysfs_notify() so the sysfs value supports poll().
Signed-off-by: Jon Flatley <jflat@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-usb

@@ -219,7 +219,14 @@ Description:
 		ports and report them to the kernel. This attribute is to expose
 		the number of over-current situation occurred on a specific port
 		to user space. This file will contain an unsigned 32 bit value
-		which wraps to 0 after its maximum is reached.
+		which wraps to 0 after its maximum is reached. This file supports
+		poll() for monitoring changes to this value in user space.
+
+		Any time this value changes the corresponding hub device will send a
+		udev event with the following attributes:
+
+		OVER_CURRENT_PORT=/sys/bus/usb/devices/.../(hub interface)/portX
+		OVER_CURRENT_COUNT=[current value of this sysfs attribute]
 
 What:		/sys/bus/usb/devices/.../(hub interface)/portX/usb3_lpm_permit
 Date:		November 2015

drivers/usb/core/hub.c

@@ -28,6 +28,7 @@
 #include <linux/mutex.h>
 #include <linux/random.h>
 #include <linux/pm_qos.h>
+#include <linux/kobject.h>
 
 #include <linux/uaccess.h>
 #include <asm/byteorder.h>
@@ -5147,6 +5148,40 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
 	usb_lock_port(port_dev);
 }
 
+/* Handle notifying userspace about hub over-current events */
+static void port_over_current_notify(struct usb_port *port_dev)
+{
+	static char *envp[] = { NULL, NULL, NULL };
+	struct device *hub_dev;
+	char *port_dev_path;
+
+	sysfs_notify(&port_dev->dev.kobj, NULL, "over_current_count");
+
+	hub_dev = port_dev->dev.parent;
+
+	if (!hub_dev)
+		return;
+
+	port_dev_path = kobject_get_path(&port_dev->dev.kobj, GFP_KERNEL);
+	if (!port_dev_path)
+		return;
+
+	envp[0] = kasprintf(GFP_KERNEL, "OVER_CURRENT_PORT=%s", port_dev_path);
+	if (!envp[0])
+		return;
+
+	envp[1] = kasprintf(GFP_KERNEL, "OVER_CURRENT_COUNT=%u",
+			port_dev->over_current_count);
+	if (!envp[1])
+		goto exit;
+
+	kobject_uevent_env(&hub_dev->kobj, KOBJ_CHANGE, envp);
+
+	kfree(envp[1]);
+exit:
+	kfree(envp[0]);
+}
+
 static void port_event(struct usb_hub *hub, int port1)
 		__must_hold(&port_dev->status_lock)
 {
@@ -5189,6 +5224,7 @@ static void port_event(struct usb_hub *hub, int port1)
 	if (portchange & USB_PORT_STAT_C_OVERCURRENT) {
 		u16 status = 0, unused;
 		port_dev->over_current_count++;
+		port_over_current_notify(port_dev);
 
 		dev_dbg(&port_dev->dev, "over-current change #%u\n",
 			port_dev->over_current_count);