USB: add usbfs ioctl to retrieve the connection speed

The usbfs interface does not provide any way for the user to learn the
speed at which a device is connected.  The current API includes a
USBDEVFS_CONNECTINFO ioctl, but all it provides is the device's
address and a one-bit value indicating whether the connection is low
speed.  That may have sufficed in the era of USB-1.1, but it isn't
good enough today.

This patch introduces a new ioctl, USBDEVFS_GET_SPEED, which returns a
numeric value indicating the speed of the connection: unknown, low,
full, high, wireless, super, or super-plus.

Similar information (not exactly the same) is available through sysfs,
but it seems reasonable to provide the actual value in usbfs.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Reinhard Huck <reinhard.huck@thesycon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/devio.c

@@ -2537,6 +2537,9 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 	case USBDEVFS_DROP_PRIVILEGES:
 		ret = proc_drop_privileges(ps, p);
 		break;
+	case USBDEVFS_GET_SPEED:
+		ret = ps->dev->speed;
+		break;
 	}
 
  done:

include/uapi/linux/usbdevice_fs.h

@@ -156,6 +156,11 @@ struct usbdevfs_streams {
 	unsigned char eps[0];
 };
 
+/*
+ * USB_SPEED_* values returned by USBDEVFS_GET_SPEED are defined in
+ * linux/usb/ch9.h
+ */
+
 #define USBDEVFS_CONTROL           _IOWR('U', 0, struct usbdevfs_ctrltransfer)
 #define USBDEVFS_CONTROL32           _IOWR('U', 0, struct usbdevfs_ctrltransfer32)
 #define USBDEVFS_BULK              _IOWR('U', 2, struct usbdevfs_bulktransfer)
@@ -190,5 +195,6 @@ struct usbdevfs_streams {
 #define USBDEVFS_ALLOC_STREAMS     _IOR('U', 28, struct usbdevfs_streams)
 #define USBDEVFS_FREE_STREAMS      _IOR('U', 29, struct usbdevfs_streams)
 #define USBDEVFS_DROP_PRIVILEGES   _IOW('U', 30, __u32)
+#define USBDEVFS_GET_SPEED         _IO('U', 31)
 
 #endif /* _UAPI_LINUX_USBDEVICE_FS_H */