From: Kirill A. Korinsky <kirill@korins.ky>
Subject: sys/uvideo: clarify bulk endpoint stream closure
To: OpenBSD tech <tech@openbsd.org>
Cc: Marcus Glocker <mglocker@openbsd.org>, Laurence Tratt <laurie@tratt.net>
Date: Tue, 11 Feb 2025 09:13:08 +0100

tech@,

Right now, we're using the same method to close the video stream for
both bulk and non-bulk endpoints. This approach switches back to the
default (zero) interface and turns off the camera LED. While this logic
is valid for non-bulk endpoints, bulk endpoints always use the default
interface. As a result, the switch is likely ignored by the device or
may trigger a reset.

Some devices can enter a broken state and won't function until they are
reattached. One such example is the Elgato Game Capture HD60 S+. After
the user presses 'q' in ffmpeg to stop the stream, the device becomes
unusable until it is reattached. For embedded USB webcams, this issue
could require a reboot to resolve.

UVC does not specify how to notify a bulk-based device when the video
stream stops. Both Linux and Windows send a CLEAR_FEATURE(HALT) request
to the video streaming bulk endpoint.

I've implemented the same logic in our codebase.

I've tested it on my bulk webcams, and no regressions were observed, and by
Laurence (cc'ed) who has access to Elgato device and it fixed the issue.

Tests? Ok?

Index: sys/dev/usb/uvideo.c
===================================================================
RCS file: /home/cvs/src/sys/dev/usb/uvideo.c,v
diff -u -p -r1.237 uvideo.c
--- sys/dev/usb/uvideo.c	6 Feb 2025 13:15:50 -0000	1.237
+++ sys/dev/usb/uvideo.c	8 Feb 2025 22:14:19 -0000
@@ -2031,15 +2031,27 @@ uvideo_vs_close(struct uvideo_softc *sc)
 		sc->sc_vs_cur->pipeh = NULL;
 	}
 
-	/*
-	 * Some devices need time to shutdown before we switch back to
-	 * the default interface (0).  Not doing so can leave the device
-	 * back in a undefined condition.
-	 */
-	usbd_delay_ms(sc->sc_udev, 100);
+	if (sc->sc_vs_cur->bulk_endpoint) {
+		/*
+		 * UVC doesn't specify how to inform a bulk-based device
+		 * when the video stream is stopped. Both, Linux and
+		 * Windows send a CLEAR_FEATURE(HALT) request to the
+		 * video streaming bulk endpoint.
+		 */
+		if (usbd_clear_endpoint_feature(sc->sc_udev,
+		    sc->sc_vs_cur->endpoint, UF_ENDPOINT_HALT))
+			printf("%s: clear endpoints failed!\n", __func__);
+	} else {
+		/*
+		 * Some devices need time to shutdown before we switch back to
+		 * the default interface (0).  Not doing so can leave the device
+		 * back in a undefined condition.
+		 */
+		usbd_delay_ms(sc->sc_udev, 100);
 
-	/* switch back to default interface (turns off cam LED) */
-	(void)usbd_set_interface(sc->sc_vs_cur->ifaceh, 0);
+		/* switch back to default interface (turns off cam LED) */
+		(void)usbd_set_interface(sc->sc_vs_cur->ifaceh, 0);
+	}
 }
 
 usbd_status

-- 
wbr, Kirill