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    Subject[PATCH 3.12 064/170] xhci: correct burst count field for isoc transfers on 1.0 xhci hosts
    Date
    From: Mathias Nyman <mathias.nyman@linux.intel.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit 3213b151387df0b95f4eada104f68eb1c1409cb3 upstream.

    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."

    Suggested-by: ShiChun Ma <masc2008@qq.com>
    Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    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 1dbfb52dbcd6..6118e292d5df 100644
    --- a/drivers/usb/host/xhci-ring.c
    +++ b/drivers/usb/host/xhci-ring.c
    @@ -3633,7 +3633,7 @@ 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;
    }

    /*
    --
    2.0.0


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