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

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Message-Id: <1403619322-24704-2-git-send-email-mathias.nyman@linux.intel.com>
Date:	Tue, 24 Jun 2014 17:14:41 +0300
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	<gregkh@...uxfoundation.org>
Cc:	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<dan.j.williams@...el.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	stable@...r.kernel.org
Subject: [PATCH 2/5] xhci: correct burst count field for isoc transfers on 1.0 xhci hosts

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@...r.kernel.org # 3.0
Suggested-by: ShiChun Ma <masc2008@...com>
Signed-off-by: Mathias Nyman <mathias.nyman@...ux.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

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