usb: gadget: composite: Return SSP Dev Cap descriptor

If a gadget supports SuperSpeedPlus or higher speeds, return a
SuperSpeedPlus USB Device Capability descriptor.

Currently this implementation returns a fixed descriptor with typical
values set.

Signed-off-by: John Youn <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/composite.c

···
 	ss_cap->bU1devExitLat = dcd_config_params.bU1devExitLat;
 	ss_cap->bU2DevExitLat = dcd_config_params.bU2DevExitLat;
 
+	/* The SuperSpeedPlus USB Device Capability descriptor */
+	if (gadget_is_superspeed_plus(cdev->gadget)) {
+		struct usb_ssp_cap_descriptor *ssp_cap;
+
+		ssp_cap = cdev->req->buf + le16_to_cpu(bos->wTotalLength);
+		bos->bNumDeviceCaps++;
+
+		/*
+		 * Report typical values.
+		 */
+
+		le16_add_cpu(&bos->wTotalLength, USB_DT_USB_SSP_CAP_SIZE(1));
+		ssp_cap->bLength = USB_DT_USB_SSP_CAP_SIZE(1);
+		ssp_cap->bDescriptorType = USB_DT_DEVICE_CAPABILITY;
+		ssp_cap->bDevCapabilityType = USB_SSP_CAP_TYPE;
+
+		/* SSAC = 1 (2 attributes) */
+		ssp_cap->bmAttributes = cpu_to_le32(1);
+
+		/* Min RX/TX Lane Count = 1 */
+		ssp_cap->wFunctionalitySupport = (1 << 8) | (1 << 12);
+
+		/*
+		 * bmSublinkSpeedAttr[0]:
+		 *   ST  = Symmetric, RX
+		 *   LSE =  3 (Gbps)
+		 *   LP  =  1 (SuperSpeedPlus)
+		 *   LSM = 10 (10 Gbps)
+		 */
+		ssp_cap->bmSublinkSpeedAttr[0] =
+			(3 << 4) | (1 << 14) | (0xa << 16);
+		/*
+		 * bmSublinkSpeedAttr[1] =
+		 *   ST  = Symmetric, TX
+		 *   LSE =  3 (Gbps)
+		 *   LP  =  1 (SuperSpeedPlus)
+		 *   LSM = 10 (10 Gbps)
+		 */
+		ssp_cap->bmSublinkSpeedAttr[1] =
+			(3 << 4) | (1 << 14) | (0xa << 16) | (1 << 7);
+	}
+
 	return le16_to_cpu(bos->wTotalLength);
 }