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USB: xhci: Avoid compiler reordering in Link TRB giveback.

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Force the compiler to write the cycle bit of the Link TRB last.  This
ensures that the hardware doesn't think it owns the Link TRB before we set
the chain bit.  Reported by Oliver in this thread:
	http://marc.info/?l=linux-usb&m=124091532410219&w=2

Reported-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Sarah Sharp 2009-04-29 19:05:58 -07:00 committed by Greg Kroah-Hartman
parent c96a2b81f3
commit b7116ebca4
1 changed files with 3 additions and 2 deletions
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5
drivers/usb/host/xhci-ring.c
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@ -183,13 +183,14 @@ static void inc_enq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer
while (last_trb(xhci, ring, ring->enq_seg, next)) {
if (!consumer) {
if (ring != xhci->event_ring) {
next->link.control &= ~TRB_CHAIN;
next->link.control |= chain;
/* Give this link TRB to the hardware */
wmb();
if (next->link.control & TRB_CYCLE)
next->link.control &= (u32) ~TRB_CYCLE;
else
next->link.control |= (u32) TRB_CYCLE;
next->link.control &= ~TRB_CHAIN;
next->link.control |= chain;
}
/* Toggle the cycle bit after the last ring segment. */
if (last_trb_on_last_seg(xhci, ring, ring->enq_seg, next)) {