xhci: Fix errors in the running total calculations in the TRB math

Calculations like

	running_total = TRB_MAX_BUFF_SIZE -
		(sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
	if (running_total != 0)
		num_trbs++;

are incorrect, because running_total can never be zero, so the if()
expression will never be true. I think the intention was that
running_total be in the range of 0 to TRB_MAX_BUFF_SIZE-1, not 1
to TRB_MAX_BUFF_SIZE. So adding a

	running_total &= TRB_MAX_BUFF_SIZE - 1;

fixes the problem.

This patch should be queued for stable kernels back to 2.6.31.

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@kernel.org

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1071411d6dfc099406e86c84f3927ed61791fd3f..dbbeec96ce1df2669431ee74b0cfde96109fd8f3 100644 (file)
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2369,6 +2369,7 @@ static unsigned int count_sg_trbs_needed(struct xhci_hcd *xhci, struct urb *urb)
                /* Scatter gather list entries may cross 64KB boundaries */
                running_total = TRB_MAX_BUFF_SIZE -
                        (sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
+               running_total &= TRB_MAX_BUFF_SIZE - 1;
                if (running_total != 0)
                        num_trbs++;
 
@@ -2661,6 +2662,7 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
        /* How much data is (potentially) left before the 64KB boundary? */
        running_total = TRB_MAX_BUFF_SIZE -
                (urb->transfer_dma & (TRB_MAX_BUFF_SIZE - 1));
+       running_total &= TRB_MAX_BUFF_SIZE - 1;
 
        /* If there's some data on this 64KB chunk, or we have to send a
         * zero-length transfer, we need at least one TRB
@@ -2884,6 +2886,7 @@ static int count_isoc_trbs_needed(struct xhci_hcd *xhci,
        td_len = urb->iso_frame_desc[i].length;
 
        running_total = TRB_MAX_BUFF_SIZE - (addr & (TRB_MAX_BUFF_SIZE - 1));
+       running_total &= TRB_MAX_BUFF_SIZE - 1;
        if (running_total != 0)
                num_trbs++;