Re: port-arm/60021: USB-only boot: uhub0 attaches but uhub1 never appears, no hotplug events; SD-boot sees hub+umass fine

I will give it a go (build /wUSB_DEBUG), and report.  I also have an RPi3B
(not +), and will try there, too.

LLMs say not waiting long enough for the attach, probably.

On Tue, Aug 4, 2026 at 6:35 AM Taylor R Campbell via gnats <
[email protected]> wrote:

> The following reply was made to PR port-arm/60021; it has been noted by
> GNATS.
>
> From: Taylor R Campbell <[email protected]>
> To: Nick Hudson <[email protected]>
> Cc: [email protected], [email protected], [email protected]
> Subject: Re: port-arm/60021: USB-only boot: uhub0 attaches but uhub1 never
>         appears, no hotplug events; SD-boot sees hub+umass fine
> Date: Tue, 4 Aug 2026 13:34:02 +0000
>
>  > Date: Sat, 21 Feb 2026 10:39:41 +0000
>  > From: Nick Hudson <[email protected]>
>  >=20
>  > This is almost certainly that autoconf doesn't wait (long enough) for
>  > sub-ordintate hubs
>  >=20
>  > https://nxr.netbsd.org/xref/src/sys/dev/usb/uhub.c#880
>  >=20
>  >      880     mutex_enter(&sc->sc_lock);
>  >      881     sc->sc_explorepending =3D false;
>  >      882     for (int i =3D 0; i < sc->sc_statuslen; i++) {
>  >      883             if (sc->sc_statuspend[i] !=3D 0) {
>  >      884                     memcpy(sc->sc_status, sc->sc_statuspend,
>  >      885                         sc->sc_statuslen);
>  >      886                     memset(sc->sc_statuspend, 0,
> sc->sc_statuslen);
>  >      887                     usb_needs_explore(sc->sc_hub);
>  >      888                     break;
>  >      889             }
>  >      890     }
>  >      891     mutex_exit(&sc->sc_lock);
>  >      892     if (sc->sc_first_explore) {
>  >      893             config_pending_decr(sc->sc_dev);
>  >      894             sc->sc_first_explore =3D false;
>  >      895     }
>
>  I don't understand, doesn't it wait for subordinate hubs?  Maybe the
>  USB hub just doesn't report the device ready at first?
>
>  Here's a fuller picture of the logic -- note that uhub_explore will
>  _synchronously_ attach autoconf drivers for the devices it finds on
>  the hub, and then uhub_attach will _also_ config_pending_incr:
>
>      529 usbd_status
>      530 uhub_explore(struct usbd_device *dev)
>      531 {
>  ...
>      598        for (port =3D 1; port <=3D hd->bNbrPorts; port++) {
>      599                up =3D &dev->ud_hub->uh_ports[port - 1];
>  ...
>      848                /* Get device info and set its address. */
>      849                err =3D usbd_new_device(sc->sc_dev, dev->ud_bus,
>      850                          dev->ud_depth + 1, speed, port, up);
>  ...
>      858                if (err) {
>  ...
>      872                } else {
>  ...
>      878                        if (up->up_dev->ud_hub)
>      879
> up->up_dev->ud_hub->uh_explore(up->up_dev);
>      880                }
>      881        }
>      882        mutex_enter(&sc->sc_lock);
>      883        sc->sc_explorepending =3D false;
>      884        for (int i =3D 0; i < sc->sc_statuslen; i++) {
>      885                if (sc->sc_statuspend[i] !=3D 0) {
>      886                        memcpy(sc->sc_status, sc->sc_statuspend,
>      887                            sc->sc_statuslen);
>      888                        memset(sc->sc_statuspend, 0,
> sc->sc_statuslen);
>      889                        usb_needs_explore(sc->sc_hub);
>      890                        break;
>      891                }
>      892        }
>      893        mutex_exit(&sc->sc_lock);
>      894        if (sc->sc_first_explore) {
>      895                config_pending_decr(sc->sc_dev);
>      896                sc->sc_first_explore =3D false;
>      897        }
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/uhub.c?r=3D1.163#529
>
>  usbd_new_device synchronously attaches autoconf drivers:
>
>     1394 usbd_status
>     1395 usbd_new_device(device_t parent, struct usbd_bus *bus, int depth,
> i=
>  nt speed,
>     1396     int port, struct usbd_port *up)
>     1397 {
>  ...
>     1606        if (port =3D=3D 0) { /* root hub */
>     1607                KASSERT(addr =3D=3D 1);
>     1608                usbd_attach_roothub(parent, dev);
>     1609                return USBD_NORMAL_COMPLETION;
>     1610        }
>     1611=20
>     1612        err =3D usbd_probe_and_attach(parent, dev, port, addr);
>     1613        if (err) {
>     1614                usbd_remove_device(dev, up);
>     1615                return err;
>     1616        }
>     1617=20
>     1618        return USBD_NORMAL_COMPLETION;
>     1619 }
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/usb_subr.c?r=3D1.281#1388
>
>     1047 usbd_status
>     1048 usbd_attach_roothub(device_t parent, struct usbd_device *dev)
>     1049 {
>  ...
>     1065        dv =3D config_found(parent, &uaa, NULL,
>     1066            CFARGS(.iattr =3D "usbroothubif"));
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/usb_subr.c?r=3D1.281#1047
>
>     1270 usbd_status
>     1271 usbd_probe_and_attach(device_t parent, struct usbd_device *dev,
>     1272     int port, int addr)
>     1273 {
>  ...
>     1283        err =3D usbd_attachwholedevice(parent, dev, port, 0);
>     1284        if (dev->ud_nifaces_claimed || err)
>     1285                return err;
>  ...
>     1290        for (confi =3D 0; confi < dd->bNumConfigurations; confi++)
> {
>  ...
>     1305                err =3D usbd_attachinterfaces(parent, dev, port,
> NULL);
>  ...
>     1313                if (dev->ud_nifaces_claimed || err)
>     1314                        return err;
>     1315        }
>  ...
>     1324        err =3D usbd_attachwholedevice(parent, dev, port, 1);
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/usb_subr.c?r=3D1.281#1270
>
>     1129 static usbd_status
>     1130 usbd_attachwholedevice(device_t parent, struct usbd_device *dev,
> in=
>  t port,
>     1131     int usegeneric)
>     1132 {
>  ...
>     1161        dv =3D config_found(parent, &uaa, usbd_print,
>     1162                          CFARGS(.submatch =3D config_stdsubmatch,
>     1163                                 .iattr =3D "usbdevif",
>     1164                                 .locators =3D dlocs));
>  ...
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/usb_subr.c?r=3D1.281#1129
>
>     1177 static usbd_status
>     1178 usbd_attachinterfaces(device_t parent, struct usbd_device *dev,
>     1179     int port, const int *locators)
>     1180 {
>  ...
>     1242                dv =3D config_found(parent, &uiaa, usbd_ifprint,
>     1243                                  CFARGS(.submatch =3D
> config_stdsubmatch,
>     1244                                         .iattr =3D "usbifif",
>     1245                                         .locators =3D ilocs));
>
>  uhub is only at one of these (usbdevif or usbifif), but the point is
>  the attach happens synchronously for subordinate hubs, before
>  uhub_explore gets to config_pending_decr.
>
>  And in uhub_attach, pretty much the first thing it does is
>  config_pending_incr -- and it also sets the hub of the USB device to
>  be the one it just created, so uhub_attach's call to uh_explore should
>  take care of this:
>
>      299 static void
>      300 uhub_attach(device_t parent, device_t self, void *aux)
>      301 {
>  ...
>      318        config_pending_incr(self);
>  ...
>      371        hub =3D kmem_alloc(sizeof(*hub) + (nports-1) *
> sizeof(struct usbd_=
>  port),
>      372            KM_SLEEP);
>      373        dev->ud_hub =3D hub;
>      374        dev->ud_hub->uh_hubsoftc =3D sc;
>      375        hub->uh_explore =3D uhub_explore;
>      376        hub->uh_hubdesc =3D hubdesc;
>
>  https://nxr.netbsd.org/xref/src/sys/dev/usb/uhub.c?r=3D1.163#529
>
>  As noted above, uhub_explore even explores the subordinate hubs
>  synchronously too by calling uh_explore!
>
>  So, does the USB device not appear to be connected at the time of the
>  initial probe, perhaps?
>
>  Building with USB_DEBUG and enabling usb_debug=3D1 so you can drop into
>  ddb and `show kernhist usbhist' might help.
>
>