USB: xhci: Don't flush doorbell writes.

To tell the host controller that there are transfers on the endpoint
rings, we need to ring the endpoint doorbell.  This is a PCI MMIO write,
which can be delayed until another register read is queued.

The previous code would flush the doorbell write by reading the doorbell
register after the write.  This may take time, and it's not necessary to
force the host controller to know about the transfers right away.  Don't
flush the doorbell register writes.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 6860e9f097bb3543e6fce35f2fcd0d3582f66b18..bc3f4f427065901059737ca960bd03d0fa75a8fc 100644 (file)
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -337,11 +337,6 @@ static void ring_ep_doorbell(struct xhci_hcd *xhci,
                field = xhci_readl(xhci, db_addr) & DB_MASK;
                field |= EPI_TO_DB(ep_index) | STREAM_ID_TO_DB(stream_id);
                xhci_writel(xhci, field, db_addr);
-               /* Flush PCI posted writes - FIXME Matthew Wilcox says this
-                * isn't time-critical and we shouldn't make the CPU wait for
-                * the flush.
-                */
-               xhci_readl(xhci, db_addr);
        }
 }