The current UHCI driver constructs the bulk transfer queue as a simple
list with a 'terminate' marker on the end. This means that the bulk queue
runs only once per frame period. This is OK for devices with large input
buffers, but in the case of a large transfer to a device with a small
input buffer, it limits the throughput to 1 buffer per frame time (nominal
1ms). In the case of the hardware I am using, the buffer is 128 bytes, so
I only get 128000 bytes/sec throughput with the UHCI driver, compared to
over 200000 bytes/sec with OHCI.
If the UHCI driver arranges the bulk transfer queue as a circular list,
transfers will be retried repeatedly in what would otherwise be wasted
time at the end of the frame; this is similar to what OHCI does. In fact
in my application the patched UHCI driver comes out slightly better than
OHCI (though this may be other factors like CPU speed).
The patch to do this appears to be very simple (this diff is against
-stable as my -current machine is OHCI, but the code is identical in
-current).
Index: uhci.c
===================================================================
RCS file: /repository/src/sys/dev/usb/uhci.c,v
retrieving revision 1.40.2.7
diff -c -r1.40.2.7 uhci.c
*** uhci.c 31 Oct 2000 23:23:29 -0000 1.40.2.7
--- uhci.c 15 Dec 2001 23:19:17 -0000
***************
*** 371,377 ****
bsqh = uhci_alloc_sqh(sc);
if (bsqh == NULL)
return (USBD_NOMEM);
! bsqh->qh.qh_hlink = LE(UHCI_PTR_T); /* end of QH chain */
bsqh->qh.qh_elink = LE(UHCI_PTR_T);
sc->sc_bulk_start = sc->sc_bulk_end = bsqh;
--- 371,378 ----
bsqh = uhci_alloc_sqh(sc);
if (bsqh == NULL)
return (USBD_NOMEM);
! bsqh->hlink = bsqh; /* Circular QH chain */
! bsqh->qh.qh_hlink = LE(bsqh->physaddr | UHCI_PTR_Q);
bsqh->qh.qh_elink = LE(UHCI_PTR_T);
sc->sc_bulk_start = sc->sc_bulk_end = bsqh;
***************
*** 890,896 ****
DPRINTFN(10, ("uhci_remove_bulk: sqh=%p\n", sqh));
for (pqh = sc->sc_bulk_start; pqh->hlink != sqh; pqh = pqh->hlink)
#if defined(DIAGNOSTIC) || defined(UHCI_DEBUG)
! if (LE(pqh->qh.qh_hlink) & UHCI_PTR_T) {
printf("uhci_remove_bulk: QH not found\n");
return;
}
--- 891,897 ----
DPRINTFN(10, ("uhci_remove_bulk: sqh=%p\n", sqh));
for (pqh = sc->sc_bulk_start; pqh->hlink != sqh; pqh = pqh->hlink)
#if defined(DIAGNOSTIC) || defined(UHCI_DEBUG)
! if (pqh == sc->sc_bulk_end) {
printf("uhci_remove_bulk: QH not found\n");
return;
}
