linux-kernel - [PATCH 3.2 09/94] xhci: correct burst count field for isoc transfers on 1.0 xhci hosts

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Message-ID: <lsq.1407170911.907082447@decadent.org.uk>
Date:	Mon, 04 Aug 2014 17:48:31 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "ShiChun Ma" <masc2008@...com>,
	"Mathias Nyman" <mathias.nyman@...ux.intel.com>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: [PATCH 3.2 09/94] xhci: correct burst count field for isoc
 transfers on 1.0 xhci hosts

3.2.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mathias Nyman <mathias.nyman@...ux.intel.com>

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@...com>
Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/host/xhci-ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3521,7 +3521,7 @@ static unsigned int xhci_get_burst_count
 		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;
 }
 
 /*

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