usb: core: introduce per-port over-current counters

For some userspace applications information on the number of
over-current conditions at specific USB hub ports is relevant.

In our case we have a series of USB hardware (using the cp210x driver)
which communicates using a proprietary protocol. These devices sometimes
trigger an over-current situation on some hubs. In case of such an
over-current situation the USB devices offer an interface for reducing
the max used power. As these conditions are quite rare and imply
performance reductions of the device we don't want to reduce the max
power always.

Therefore give user-space applications the possibility to react
adequately by introducing an over_current_counter in the usb port struct
which is exported via sysfs.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-usb

@@ -189,6 +189,16 @@ Description:
 		The file will read "hotplug", "wired" and "not used" if the
 		information is available, and "unknown" otherwise.
 
+What:		/sys/bus/usb/devices/.../(hub interface)/portX/over_current_count
+Date:		February 2018
+Contact:	Richard Leitner <richard.leitner@skidata.com>
+Description:
+		Most hubs are able to detect over-current situations on their
+		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.
+
 What:		/sys/bus/usb/devices/.../(hub interface)/portX/usb3_lpm_permit
 Date:		November 2015
 Contact:	Lu Baolu <baolu.lu@linux.intel.com>

drivers/usb/core/hub.c

@@ -5104,8 +5104,10 @@ 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++;
 
-		dev_dbg(&port_dev->dev, "over-current change\n");
+		dev_dbg(&port_dev->dev, "over-current change #%u\n",
+			port_dev->over_current_count);
 		usb_clear_port_feature(hdev, port1,
 				USB_PORT_FEAT_C_OVER_CURRENT);
 		msleep(100);	/* Cool down */

drivers/usb/core/hub.h

@@ -96,6 +96,7 @@ struct usb_port {
 	enum usb_port_connect_type connect_type;
 	usb_port_location_t location;
 	struct mutex status_lock;
+	u32 over_current_count;
 	u8 portnum;
 	unsigned int is_superspeed:1;
 	unsigned int usb3_lpm_u1_permit:1;

drivers/usb/core/port.c

@@ -41,6 +41,15 @@ static ssize_t connect_type_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(connect_type);
 
+static ssize_t over_current_count_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct usb_port *port_dev = to_usb_port(dev);
+
+	return sprintf(buf, "%u\n", port_dev->over_current_count);
+}
+static DEVICE_ATTR_RO(over_current_count);
+
 static ssize_t usb3_lpm_permit_show(struct device *dev,
 			      struct device_attribute *attr, char *buf)
 {
@@ -109,6 +118,7 @@ static DEVICE_ATTR_RW(usb3_lpm_permit);
 
 static struct attribute *port_dev_attrs[] = {
 	&dev_attr_connect_type.attr,
+	&dev_attr_over_current_count.attr,
 	NULL,
 };