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Subject[PATCH] [156/275] xhci: Fix errors in the running total calculations in the TRB math
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Paul Zimmerman <Paul.Zimmerman@synopsys.com>

commit 5807795bd4dececdf553719cc02869e633395787 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
drivers/usb/host/xhci-ring.c | 2 ++
1 file changed, 2 insertions(+)

Index: linux-2.6.35.y/drivers/usb/host/xhci-ring.c
===================================================================
--- linux-2.6.35.y.orig/drivers/usb/host/xhci-ring.c 2011-03-29 23:03:01.485262166 -0700
+++ linux-2.6.35.y/drivers/usb/host/xhci-ring.c 2011-03-29 23:54:34.277125360 -0700
@@ -1891,6 +1891,7 @@
/* 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++;

@@ -2171,6 +2172,7 @@
/* 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

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