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

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1071411d6dfc..dbbeec96ce1d 100644
--- 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++;