[PATCH 2/5] xhci: correct burst count field for isoc transfers on 1.0 xhci hosts

Mathias Nyman
2014-06-24T14:14:41Z

The transfer burst count (TBC) field in xhci 1.0 hosts should be set
to the number of bursts needed to transfer all packets in a isoc TD.
Supported values are 0-2 (1 to 3 bursts per service interval).

Formula for TBC calculation is given in xhci spec section 4.11.2.3:
TBC = roundup( Transfer Descriptor Packet Count / Max Burst Size +1 ) - 1

This patch should be applied to stable kernels since 3.0 that contain
the commit 5cd43e33b9519143f06f507dd7cbee6b7a621885
"xhci 1.0: Set transfer burst count field."

Cc: stable@vger.kernel.org # 3.0
Suggested-by: ShiChun Ma <masc2008@qq.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
drivers/usb/host/xhci-ring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 71657d3..749fc68 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3537,7 +3537,7 @@ static unsigned int xhci_get_burst_count(struct xhci_hcd *xhci,
return 0;

max_burst = urb->ep->ss_ep_comp.bMaxBurst;
- return roundup(total_packet_count, max_burst + 1) - 1;
+ return DIV_ROUND_UP(total_packet_count, max_burst + 1) - 1;
}

/*
--
1.8.3.2