[3.16.y-ckt stable] Patch "xhci: Allocate correct amount of scratchpad buffers" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Thu Mar 19 10:12:32 UTC 2015

This is a note to let you know that I have just added a patch titled

    xhci: Allocate correct amount of scratchpad buffers

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see



>From 1badc7aace77eefc5f1cf76a1bc1bf57edca2b43 Mon Sep 17 00:00:00 2001
From: Mathias Nyman <mathias.nyman at linux.intel.com>
Date: Tue, 24 Feb 2015 18:27:01 +0200
Subject: xhci: Allocate correct amount of scratchpad buffers

commit 6596a926b0b6c80b730a1dd2fa91908e0a539c37 upstream.

Include the high order bit fields for Max scratchpad buffers when
calculating how many scratchpad buffers are needed.

I'm suprised this hasn't caused more issues, we never allocated more than
32 buffers even if xhci needed more. Either we got lucky and xhci never
really used past that area, or then we got enough zeroed dma memory anyway.

Should be backported as far back as possible

Reported-by: Tim Chen <tim.c.chen at linux.intel.com>
Tested-by: Tim Chen <tim.c.chen at linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman at linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/usb/host/xhci.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 00ed780c0563..c57261affada 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -88,9 +88,10 @@ struct xhci_cap_regs {
 #define HCS_IST(p)		(((p) >> 0) & 0xf)
 /* bits 4:7, max number of Event Ring segments */
 #define HCS_ERST_MAX(p)		(((p) >> 4) & 0xf)
+/* bits 21:25 Hi 5 bits of Scratchpad buffers SW must allocate for the HW */
 /* bit 26 Scratchpad restore - for save/restore HW state - not used yet */
-/* bits 27:31 number of Scratchpad buffers SW must allocate for the HW */
-#define HCS_MAX_SCRATCHPAD(p)   (((p) >> 27) & 0x1f)
+/* bits 27:31 Lo 5 bits of Scratchpad buffers SW must allocate for the HW */
+#define HCS_MAX_SCRATCHPAD(p)   ((((p) >> 16) & 0x3e0) | (((p) >> 27) & 0x1f))

 /* HCSPARAMS3 - hcs_params3 - bitmasks */
 /* bits 0:7, Max U1 to U0 latency for the roothub ports */

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