From: Ming Lei <tom.leiming@xxxxxxxxx> According to ehci spec 4.10.2, Advance Queue If the fetched qTD has its Active bit set to a zero, the host controller aborts the queue advance and follows the queue head's horizontal pointer to the next schedule data structure. the 'qtd' will be linked into qh hardware queue after the line below *dummy = *qtd; is executed and observed by EHCI HC, but EHCI HC won't have chance to fetch the qtd descriptor pointed by 'qtd' in qh_append_tds until the line below dummy->hw_token = token; #set Active bit here is executed by CPU and observed by EHCI HC. There is already one 'wmb' to order writing to 'dummy'/'qtd' descriptors and writing 'token' to 'dummy' descriptor(set Active bit), so the 1st wmb is not needed and can be removed. Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx> --- drivers/usb/host/ehci-q.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c index 5996ad5..00443d2 100644 --- a/drivers/usb/host/ehci-q.c +++ b/drivers/usb/host/ehci-q.c @@ -1057,7 +1057,7 @@ static struct ehci_qh *qh_append_tds ( */ token = qtd->hw_token; qtd->hw_token = HALT_BIT(ehci); - wmb (); + dummy = qh->dummy; dma = dummy->qtd_dma; -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
