usb: usbtest: support superspeed device capbility descriptor test

In Test 9 of usbtest module, it is used for performing chapter 9 tests N
times.

SuperSpeed USB Device Capability descriptor is one of the generic
device-level capbility descriptors which added in section 9.6.2.2 of USB
3.0 spec.

This patch adds to support getting SuperSpeed USB Device Capability
descriptor test scenario for USB 3.0.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usbtest.c

@@ -628,6 +628,35 @@ static int is_good_ext(struct usbtest_dev *tdev, u8 *buf)
 	return 1;
 }
 
+static int is_good_ss_cap(struct usbtest_dev *tdev, u8 *buf)
+{
+	struct usb_ss_cap_descriptor *ss;
+
+	ss = (struct usb_ss_cap_descriptor *) buf;
+
+	if (ss->bLength != USB_DT_USB_SS_CAP_SIZE) {
+		ERROR(tdev, "bogus superspeed device capability descriptor length\n");
+		return 0;
+	}
+
+	/*
+	 * only bit[1] of bmAttributes is used for LTM and others are
+	 * reserved
+	 */
+	if (ss->bmAttributes & ~0x02) {	/* reserved == 0 */
+		ERROR(tdev, "reserved bits set in bmAttributes\n");
+		return 0;
+	}
+
+	/* bits[0:3] of wSpeedSupported is used and others are reserved */
+	if (le16_to_cpu(ss->wSpeedSupported) & ~0x0f) {	/* reserved == 0 */
+		ERROR(tdev, "reserved bits set in wSpeedSupported\n");
+		return 0;
+	}
+
+	return 1;
+}
+
 /* sanity test for standard requests working with usb_control_mesg() and some
  * of the utility functions which use it.
  *
@@ -773,6 +802,14 @@ static int ch9_postconfig(struct usbtest_dev *dev)
 					return -EDOM;
 				}
 				break;
+			case USB_SS_CAP_TYPE:
+				if (buf + USB_DT_USB_SS_CAP_SIZE >
+						dev->buf + total ||
+						!is_good_ss_cap(dev, buf)) {
+					dev_err(&iface->dev, "bogus superspeed device capability descriptor\n");
+					return -EDOM;
+				}
+				break;
 			default:
 				break;
 			}