[PATCH v2 3/5] xhci: Add rmb() between reading event validity & event data access.

[Matt Evans <matt@ozlabs.org>]

On weakly-ordered systems, the reading of an event's content must occur
after reading the event's validity.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
Segher, thanks for the comment; explanation added.

 drivers/usb/host/xhci-ring.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 45f3b77..d6aa880 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2152,6 +2152,11 @@ static void xhci_handle_event(struct xhci_hcd *xhci)
 	}
 	xhci_dbg(xhci, "%s - OS owns TRB\n", __func__);
 
+	/*
+	 * Barrier between reading the TRB_CYCLE (valid) flag above and any
+	 * speculative reads of the event's flags/data below.
+	 */
+	rmb();
 	/* FIXME: Handle more event types. */
 	switch ((le32_to_cpu(event->event_cmd.flags) & TRB_TYPE_BITMASK)) {
 	case TRB_TYPE(TRB_COMPLETION):
-- 
1.7.0.4