From b7116ebca4e1a898f30ae474151fd6474327257c Mon Sep 17 00:00:00 2001 From: Sarah Sharp Date: Wed, 29 Apr 2009 19:05:58 -0700 Subject: [PATCH] USB: xhci: Avoid compiler reordering in Link TRB giveback. 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 Signed-off-by: Sarah Sharp Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/xhci-ring.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index f692e74..d42a738 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -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)) { -- 1.8.2.3