New patch to review for coreboot: 7f59b31 libpayload: ehci: Prevent some race conditions

[Nico Huber]

Nico Huber ([e-mail]) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/1902

-gerrit

commit 7f59b31c4efaadebd2897b302c381b80f7925cab
Author: Nico Huber 
Date:   Thu Nov 22 11:14:03 2012 +0100

libpayload: ehci: Prevent some race conditions

Prevent race conditions, when an interrupt-queue underrun occurred and
    the controller is currently working on our queue head or a transfer is
    still in progress.

Change-Id: Ia14f80a08071306ee5d1349780be081bfacb206a
    Signed-off-by: Nico Huber 
---
 payloads/libpayload/drivers/usb/ehci.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/payloads/libpayload/drivers/usb/ehci.c b/payloads/libpayload/drivers/usb/ehci.c
index 4ff137e..6a1cfb5 100644
--- a/payloads/libpayload/drivers/usb/ehci.c
+++ b/payloads/libpayload/drivers/usb/ehci.c
@@ -626,8 +626,14 @@ static u8 *ehci_poll_intr_queue(void *const queue)
    	intrq->head = intrq->head->next;
    }
    /* reset queue if we fully processed it after underrun */
-	else if (intrq->qh.td.next_qtd & QTD_TERMINATE) {
+	else if ((intrq->qh.td.next_qtd & QTD_TERMINATE) &&
+			/* to prevent race conditions:
+			   not our head and not active */
+			(intrq->qh.current_td_ptr !=
+			 virt_to_phys(&intrq->head->td)) &&
+			!(intrq->qh.td.token & QTD_ACTIVE)) {
    	usb_debug("resetting underrun ehci interrupt queue.\n");
+		intrq->qh.current_td_ptr = 0;
    	memset((void *)&intrq->qh.td, 0, sizeof(intrq->qh.td));
    	intrq->qh.td.next_qtd = virt_to_phys(&intrq->head->td);
    }