[PATCH v2 2/2][SRU][F/OEM-B/OEM-OSP1-B/OEM-5.6] xhci: Poll for U0 after disabling USB2 LPM

Hsuan-Yu Lin shane.lin at canonical.com
Wed Jul 15 03:30:48 UTC 2020

From: Kai-Heng Feng <kai.heng.feng at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1880519

USB2 devices with LPM enabled may interrupt the system suspend:
[  932.510475] usb 1-7: usb suspend, wakeup 0
[  932.510549] hub 1-0:1.0: hub_suspend
[  932.510581] usb usb1: bus suspend, wakeup 0
[  932.510590] xhci_hcd 0000:00:14.0: port 9 not suspended
[  932.510593] xhci_hcd 0000:00:14.0: port 8 not suspended
[  932.520323] xhci_hcd 0000:00:14.0: Port change event, 1-7, id 7, portsc: 0x400e03
[  932.591405] PM: pci_pm_suspend(): hcd_pci_suspend+0x0/0x30 returns -16
[  932.591414] PM: dpm_run_callback(): pci_pm_suspend+0x0/0x160 returns -16
[  932.591418] PM: Device 0000:00:14.0 failed to suspend async: error -16

During system suspend, USB core will let HC suspends the device if it
doesn't have remote wakeup enabled and doesn't have any children.
However, from the log above we can see that the usb 1-7 doesn't get bus
suspended due to not in U0. After a while the port finished U2 -> U0
transition, interrupts the suspend process.

The observation is that after disabling LPM, port doesn't transit to U0
immediately and can linger in U2. xHCI spec states that the
maximum exit latency for USB2 LPM should be BESL + 10us. The BESL for
the affected device is advertised as 400us, which is still not enough
based on my testing result.

So let's use the maximum permitted latency, 10000, to poll for U0
status to solve the issue.

Cc: stable at vger.kernel.org
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
Signed-off-by: Mathias Nyman <mathias.nyman at linux.intel.com>
Link: https://lore.kernel.org/r/20200624135949.22611-6-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit b3d71abd135e6919ca0b6cab463738472653ddfb)
Signed-off-by: Hsuan-Yu Lin <shane.lin at canonical.com>
 drivers/usb/host/xhci.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 305e82d6f036..f6af1da4795e 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -4474,6 +4474,9 @@ static int xhci_set_usb2_hardware_lpm(struct usb_hcd *hcd,
 			xhci_change_max_exit_latency(xhci, udev, 0);
+			readl_poll_timeout(ports[port_num]->addr, pm_val,
+					   (pm_val & PORT_PLS_MASK) == XDEV_U0,
+					   100, 10000);
 			return 0;

More information about the kernel-team mailing list