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.sh...@linux.intel.com>
Reported-by: Don Zickus <dzic...@redhat.com>
Tested-by: Don Zickus <dzic...@redhat.com>
Cc: sta...@vger.kernel.org
---
drivers/usb/core/hub.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
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
--
1.7.9
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