diff options
| -rw-r--r-- | sys/dev/usb/ohci.c | 33 |
1 files changed, 16 insertions, 17 deletions
diff --git a/sys/dev/usb/ohci.c b/sys/dev/usb/ohci.c index ff343a2..11a5049 100644 --- a/sys/dev/usb/ohci.c +++ b/sys/dev/usb/ohci.c @@ -549,32 +549,31 @@ ohci_alloc_std_chain(struct ohci_pipe *opipe, ohci_softc_t *sc, * * If/when dma has multiple segments, this will need to * properly handle fragmenting TD's. - * - * We can describe the above using maxsegsz = 4k and nsegs = 2 - * in the future. + * + * Note that if we are gathering data from multiple SMALL + * segments, e.g. mbufs, we need to do special gymnastics, + * e.g. bounce buffering or data aggregation, + * BEFORE WE GET HERE because a bulk USB transfer must + * consist of maximally sized packets right up to the end. + * A shorter than maximal packet means that it is the end + * of the transfer. If the data transfer length is a + * multiple of the packet size, then a 0 byte + * packet will be the signal of the end of transfer. + * Since packets can't cross TDs this means that + * each TD except the last one must cover an exact multiple + * of the maximal packet length. */ - if ((OHCI_PAGE_OFFSET(dataphys) + len) <= - (2 * OHCI_PAGE_SIZE)) { - /* we can handle it in this TD */ + if (OHCI_PAGE_OFFSET(dataphys) + len <= (2 * OHCI_PAGE_SIZE)) { + /* We can handle all that remains in this TD */ curlen = len; } else { - /* XXX The calculation below is wrong and could - * result in a packet that is not a multiple of the - * MaxPacketSize in the case where the buffer does not - * start on an appropriate address (like for example in - * the case of an mbuf cluster). You'll get an early - * short packet. - */ /* must use multiple TDs, fill as much as possible. */ curlen = 2 * OHCI_PAGE_SIZE - OHCI_PAGE_OFFSET(dataphys); /* the length must be a multiple of the max size */ curlen -= curlen % UGETW(opipe->pipe.endpoint->edesc->wMaxPacketSize); -#ifdef DIAGNOSTIC - if (curlen == 0) - panic("ohci_alloc_std: curlen == 0"); -#endif + KASSERT ((curlen == 0), ("ohci_alloc_std: curlen == 0")); } DPRINTFN(4,("ohci_alloc_std_chain: dataphys=0x%08x " "len=%d curlen=%d\n", |
