[ 3.5.yuz extended stable ] Patch "usb: Don't enable LPM if the exit latency is zero." has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Wed Nov 21 05:08:22 UTC 2012

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

    usb: Don't enable LPM if the exit latency is zero.

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


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

For more information about the 3.5.yuz tree, see



>From 13b3055cb739dfd704350fb63b54ae36a5fb4bff Mon Sep 17 00:00:00 2001
From: Sarah Sharp <sarah.a.sharp at linux.intel.com>
Date: Wed, 3 Oct 2012 11:18:05 -0700
Subject: [PATCH] usb: Don't enable LPM if the exit latency is zero.

commit ae8963adb4ad8c5f2a89ca1d99fb7bb721e7599f upstream.

Some USB 3.0 devices signal that they don't implement Link PM by having
all zeroes in the U1/U2 exit latencies in their SuperSpeed BOS
descriptor.  Don found that a Western Digital device he has experiences
transfer errors when LPM is enabled.  The lsusb shows the U1/U2 exit
latencies are set to zero:

Binary Object Store Descriptor:
  bLength                 5
  bDescriptorType        15
  wTotalLength           22
  bNumDeviceCaps          2
  SuperSpeed USB Device Capability:
    bLength                10
    bDescriptorType        16
    bDevCapabilityType      3
    bmAttributes         0x00
      Latency Tolerance Messages (LTM) Supported
    wSpeedsSupported   0x000e
      Device can operate at Full Speed (12Mbps)
      Device can operate at High Speed (480Mbps)
      Device can operate at SuperSpeed (5Gbps)
    bFunctionalitySupport   1
      Lowest fully-functional device speed is Full Speed (12Mbps)
    bU1DevExitLat           0 micro seconds
    bU2DevExitLat           0 micro seconds

The fix is to not enable LPM for a particular link state if we find its
corresponding exit latency is zero.

This patch should be backported to kernels as old as 3.5, that contain
the commit 1ea7e0e8e3d0f50901d335ea4178ab2aa8c88201 "USB: Add support to
enable/disable USB3 link states."

Signed-off-by: Sarah Sharp <sarah.a.sharp at linux.intel.com>
Reported-by: Don Zickus <dzickus at redhat.com>
Tested-by: Don Zickus <dzickus at redhat.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 drivers/usb/core/hub.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 70223d5..209815a 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3294,6 +3294,16 @@ static void usb_enable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
 		enum usb3_link_state state)
 	int timeout;
+	__u8 u1_mel = udev->bos->ss_cap->bU1devExitLat;
+	__le16 u2_mel = udev->bos->ss_cap->bU2DevExitLat;
+	/* If the device says it doesn't have *any* exit latency to come out of
+	 * U1 or U2, it's probably lying.  Assume it doesn't implement that link
+	 * state.
+	 */
+	if ((state == USB3_LPM_U1 && u1_mel == 0) ||
+			(state == USB3_LPM_U2 && u2_mel == 0))
+		return;

 	/* We allow the host controller to set the U1/U2 timeout internally
 	 * first, so that it can change its schedule to account for the

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