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Remove comment that doesn't seem to be true and add comments describing

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what is going on, to replace it. Slight formatting changes
Code here is alredy different to NetBSD.
MFC after:	1 week
This commit is contained in:
Julian Elischer 2005-01-03 08:52:26 +00:00
parent 2410443379
commit a8ef988f65
1 changed files with 16 additions and 17 deletions
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33
sys/dev/usb/ohci.c
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@ -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",