> > Did you consider incrementing xx->ntrb instead?
>That doesn't work either, because the status completion code needs
>xx->ntrb to be correct for the data TD to be handled correctly.
>Incrementing xx->ntrb means the number of TRBs for the data TD is
>incorrect, since it includes the (optional) zero TD's TRB.
>
>In this case the zero TD allocates a TRB but doesn't do proper
>accounting, and currently there's no place where this could be
>accounted properly.
>
>In the end it's all software, so I guess the diff will simply have
>to be bigger than just a one-liner.
> > With the diff below the produced TRB isn't accounted which might
> > lead
> > to and off-by-one.
Sorry, I missed this thread and had to re-grab the last mail from MARC.
Can't we just take account of the zero trb separately?
Index: dev/usb/xhci.c
===================================================================
RCS file: /cvs/src/sys/dev/usb/xhci.c,v
retrieving revision 1.119
diff -u -p -u -p -r1.119 xhci.c
--- dev/usb/xhci.c 31 Jul 2020 19:27:57 -0000 1.119
+++ dev/usb/xhci.c 22 Dec 2020 19:41:01 -0000
@@ -1135,6 +1135,7 @@ xhci_xfer_done(struct usbd_xfer *xfer)
i = (xp->ring.ntrb - 1);
}
xp->free_trbs += xx->ntrb;
+ xp->free_trbs += xx->zerotrb;
xx->index = -1;
xx->ntrb = 0;
@@ -1842,6 +1843,7 @@ xhci_xfer_get_trb(struct xhci_softc *sc,
switch (last) {
case -1: /* This will be a zero-length TD. */
xp->pending_xfers[xp->ring.index] = NULL;
+ xx->zerotrb = 1; /* There can only be one zero TRB per xfer. */
break;
case 0: /* This will be in a chain. */
xp->pending_xfers[xp->ring.index] = xfer;
Index: dev/usb/xhcivar.h
===================================================================
RCS file: /cvs/src/sys/dev/usb/xhcivar.h,v
retrieving revision 1.11
diff -u -p -u -p -r1.11 xhcivar.h
--- dev/usb/xhcivar.h 6 Oct 2019 17:30:00 -0000 1.11
+++ dev/usb/xhcivar.h 22 Dec 2020 19:41:01 -0000
@@ -40,6 +40,7 @@ struct xhci_xfer {
struct usbd_xfer xfer;
int index; /* Index of the last TRB */
size_t ntrb; /* Number of associated TRBs */
+ size_t zerotrb; /* Is zero len TRB required? */
};
struct xhci_ring {
