From ebb8a4e48722c8f5e04a6490b197d2fbc894a0f6 Mon Sep 17 00:00:00 2001 From: Michael Hennerich Date: Thu, 5 Aug 2010 17:53:57 -0400 Subject: [PATCH] USB: isp1760: use a write barrier to ensure proper ndelay timing The ISP1760 has some timing requirements where it has to delay a short period after a write to a register has started. However, this delay is from the time the write hits the USB chip (the ISP1760), not from the time where the processor started processing the write. So on a quick enough processor, it is sometimes possible for the write to not hit the device before we start delaying, and we then violate the part's timing requirements, so things stop working. To avoid all this, insert a write barrier after the register write and before the timing delay/register read so we can guarantee we only start counting time after the write has hit the device. Signed-off-by: Michael Hennerich Signed-off-by: Mike Frysinger Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/isp1760-hcd.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/usb/host/isp1760-hcd.c b/drivers/usb/host/isp1760-hcd.c index d1a3dfc9a40..bdba8c5d844 100644 --- a/drivers/usb/host/isp1760-hcd.c +++ b/drivers/usb/host/isp1760-hcd.c @@ -829,6 +829,7 @@ static void enqueue_an_ATL_packet(struct usb_hcd *hcd, struct isp1760_qh *qh, * almost immediately. With ISP1761, this register requires a delay of * 195ns between a write and subsequent read (see section 15.1.1.3). */ + mmiowb(); ndelay(195); skip_map = isp1760_readl(hcd->regs + HC_ATL_PTD_SKIPMAP_REG); @@ -870,6 +871,7 @@ static void enqueue_an_INT_packet(struct usb_hcd *hcd, struct isp1760_qh *qh, * almost immediately. With ISP1761, this register requires a delay of * 195ns between a write and subsequent read (see section 15.1.1.3). */ + mmiowb(); ndelay(195); skip_map = isp1760_readl(hcd->regs + HC_INT_PTD_SKIPMAP_REG); -- 2.41.0