From ae8963adb4ad8c5f2a89ca1d99fb7bb721e7599f Mon Sep 17 00:00:00 2001 From: Sarah Sharp Date: Wed, 3 Oct 2012 11:18:05 -0700 Subject: [PATCH] usb: Don't enable LPM if the exit latency is zero. 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 Reported-by: Don Zickus Tested-by: Don Zickus Cc: stable@vger.kernel.org --- 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 673ee46..8f04787 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -3415,6 +3415,16 @@ 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 -- 2.7.4