tech@,

here a diff which reads USB 3.0 speed for webcam when it is supported.

USB 3.0 Section 9.6.7 states that wBytesPerInterval is only valid for
periodic endpoints (isochronous and interrupt), so here bulk endpoints
should skip it.

But for isochronous it should increase quality.

I had tested it with two USB 3 webcam which I have (Elgato Facecam Pro
and Jabra PanaCast 20), but both of them is bulk only, no regression and
no change.

I also had tested it with two isochronous webcam which is embeded into
used laptops, but both of them USB 2. No regression and no change.

Anyway, enabled debug confirms that it dumps correct values for
interrupt endpoints on both USB 3 webcam, and it should work, I think.

BTW, Linux driver has almost the same logic.

Tests? Ok?

Index: sys/dev/usb/uvideo.c
===================================================================
RCS file: /cvs/src/sys/dev/usb/uvideo.c,v
diff -u -p -r1.240 uvideo.c
--- sys/dev/usb/uvideo.c	23 Feb 2025 14:12:15 -0000	1.240
+++ sys/dev/usb/uvideo.c	23 Feb 2025 14:53:14 -0000
@@ -138,7 +138,8 @@ usbd_status	uvideo_vs_parse_desc_format_
 usbd_status	uvideo_vs_parse_desc_frame(struct uvideo_softc *);
 usbd_status	uvideo_vs_parse_desc_frame_sub(struct uvideo_softc *,
 		    const usb_descriptor_t *);
-uint32_t	uvideo_vc_parse_max_packet_size(usb_endpoint_descriptor_t *);
+uint32_t	uvideo_vc_parse_max_packet_size(struct uvideo_softc *,
+		    usb_endpoint_descriptor_t *);
 usbd_status	uvideo_vs_parse_desc_alt(struct uvideo_softc *, int, int, int);
 usbd_status	uvideo_vs_set_alt(struct uvideo_softc *,
 		    struct usbd_interface *, int);
@@ -191,6 +192,8 @@ void		uvideo_dump_desc_output(struct uvi
 		    const usb_descriptor_t *);
 void		uvideo_dump_desc_endpoint(struct uvideo_softc *,
 		    const usb_descriptor_t *);
+void		uvideo_dump_desc_endpoint_ss_comp(struct uvideo_softc *,
+		    const usb_descriptor_t *);
 void		uvideo_dump_desc_iface_assoc(struct uvideo_softc *,
 		    const usb_descriptor_t *);
 void		uvideo_dump_desc_interface(struct uvideo_softc *,
@@ -1237,12 +1240,39 @@ uvideo_vs_parse_desc_frame_sub(struct uv
 }
 
 uint32_t
-uvideo_vc_parse_max_packet_size(usb_endpoint_descriptor_t *ed)
+uvideo_vc_parse_max_packet_size(struct uvideo_softc *sc,
+    usb_endpoint_descriptor_t *ed)
 {
 	uint32_t psize;
+	struct usbd_desc_iter iter;
+	const usb_descriptor_t *desc;
+	usb_endpoint_ss_comp_descriptor_t *esscd;
+
+	/*
+	 * USB 3.0 Section 9.6.7 states that wBytesPerInterval is only
+	 * valid for periodic endpoints (isochronous and interrupt).
+	 */
+	if (UE_GET_XFERTYPE(ed->bmAttributes) == UE_BULK)
+		goto skip_ss_comp;
+
+	usbd_desc_iter_init(sc->sc_udev, &iter);
+	while ((desc = usbd_desc_iter_next(&iter))) {
+		if (desc == (const usb_descriptor_t *)ed) {
+			desc = usbd_desc_iter_next(&iter);
+			break;
+		}
+	}
 
-	/* XXX: get USB 3.0 speed from wBytesPerInterval */
+	if (desc && sc->sc_udev->speed >= USB_SPEED_SUPER &&
+	    desc->bDescriptorType == UDESC_ENDPOINT_SS_COMP) {
+		esscd = (usb_endpoint_ss_comp_descriptor_t *)desc;
+		psize = UGETW(esscd->wBytesPerInterval);
+		DPRINTF(1, "%s: wBytesPerInterval=%d\n",
+		    DEVNAME(sc), psize);
+		return psize;
+	}
 
+skip_ss_comp:
 	psize = UGETW(ed->wMaxPacketSize);
 	psize = UE_GET_SIZE(psize) * (1 + UE_GET_TRANS(psize));
 
@@ -1321,7 +1351,7 @@ uvideo_vs_parse_desc_alt(struct uvideo_s
 		if (bulk_endpoint && !vs->bulk_endpoint)
 			goto next;
 
-		psize = uvideo_vc_parse_max_packet_size(ed);
+		psize = uvideo_vc_parse_max_packet_size(sc, ed);
 		/* save endpoint with largest bandwidth */
 		if (psize > vs->psize) {
 			vs->ifaceh = &sc->sc_udev->ifaces[iface];
@@ -1399,7 +1429,7 @@ uvideo_vs_set_alt(struct uvideo_softc *s
 			goto next;
 
 		/* save endpoint with requested bandwidth */
-		psize = uvideo_vc_parse_max_packet_size(ed);
+		psize = uvideo_vc_parse_max_packet_size(sc, ed);
 		if (psize >= max_packet_size)
 			diff = psize - max_packet_size;
 		else
@@ -2606,6 +2636,11 @@ uvideo_dump_desc_all(struct uvideo_softc
 			printf("|\n");
 			uvideo_dump_desc_endpoint(sc, desc);
 			break;
+		case UDESC_ENDPOINT_SS_COMP:
+			printf(" (UDESC_ENDPOINT_SS_COMP)\n");
+			printf("|\n");
+			uvideo_dump_desc_endpoint_ss_comp(sc, desc);
+			break;
 		case UDESC_INTERFACE:
 			printf(" (UDESC_INTERFACE)\n");
 			printf("|\n");
@@ -2741,6 +2776,21 @@ uvideo_dump_desc_endpoint(struct uvideo_
 		printf(" (UE_INTERRUPT)\n");
 	printf("wMaxPacketSize=%d\n", UGETW(d->wMaxPacketSize));
 	printf("bInterval=0x%02x\n", d->bInterval);
+}
+
+void
+uvideo_dump_desc_endpoint_ss_comp(struct uvideo_softc *sc,
+    const usb_descriptor_t *desc)
+{
+	usb_endpoint_ss_comp_descriptor_t *d;
+
+	d = (usb_endpoint_ss_comp_descriptor_t *)(uint8_t *)desc;
+
+	printf("bLength=%d\n", d->bLength);
+	printf("bDescriptorType=0x%02x\n", d->bDescriptorType);
+	printf("bMaxBurst=0x%02x\n", d->bMaxBurst);
+	printf("bmAttributes=0x%02x\n", d->bmAttributes);
+	printf("wBytesPerInterval=%d\n", UGETW(d->wBytesPerInterval));
 }
 
 void