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    Subject[PATCH 5.4 039/178] xhci: Poll for U0 after disabling USB2 LPM
    Date
    From: Kai-Heng Feng <kai.heng.feng@canonical.com>

    commit b3d71abd135e6919ca0b6cab463738472653ddfb upstream.

    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 4.23.5.2 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@vger.kernel.org
    Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
    Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
    Link: https://lore.kernel.org/r/20200624135949.22611-6-mathias.nyman@linux.intel.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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 81b54a3d29107..f913bc9344d2b 100644
    --- a/drivers/usb/host/xhci.c
    +++ b/drivers/usb/host/xhci.c
    @@ -4471,6 +4471,9 @@ static int xhci_set_usb2_hardware_lpm(struct usb_hcd *hcd,
    mutex_lock(hcd->bandwidth_mutex);
    xhci_change_max_exit_latency(xhci, udev, 0);
    mutex_unlock(hcd->bandwidth_mutex);
    + readl_poll_timeout(ports[port_num]->addr, pm_val,
    + (pm_val & PORT_PLS_MASK) == XDEV_U0,
    + 100, 10000);
    return 0;
    }
    }
    --
    2.25.1
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